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 Title Page
 Part I
 The root-knot nematode
 Sedentary types
 Migratory nematodes
 Miscellaneous types














Group Title: Bulletin
Title: Plant nematodes the grower should know
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Permanent Link: http://ufdc.ufl.edu/UF00014585/00001
 Material Information
Title: Plant nematodes the grower should know
Series Title: Bulletin
Physical Description: 47 p. : ill. ; 23 cm.
Language: English
Creator: Steiner, G ( Gotthold ), b. 1886
Florida -- Dept. of Agriculture
Soil Science Society of Florida -- Meeting
Publisher: State of Florida, Dept. of Agriculture
Place of Publication: Tallahassee
Publication Date: 1949
 Subjects
Subject: Plant nematodes -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references.
Statement of Responsibility: G. Steiner.
General Note: Reprinted from the Fourth proceedings of the Soil Science Society of Florida.
General Note: "March, 1949."
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Bibliographic ID: UF00014585
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA7059
ltuf - AMT3930
oclc - 45009096
alephbibnum - 002567633

Table of Contents
    Title Page
        Page 1
    Part I
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
    The root-knot nematode
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
    Sedentary types
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
    Migratory nematodes
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
    Miscellaneous types
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
Full Text




Bulletin No. 131


PLANT NEMATODES

THE GROWER SHOULD KNOW


STATE OF FLORIDA
DEPARTMENT OF AGRICULTURE
NATHAN MAYO, Commissioner
TALLAHASSEE


Reprinted from the Fourth Proceedings of the
Soil Science Society of Florida


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New Series


March, 1949









PLANT NEMATODES THE GROWER SHOULD KNOW

G. STEINER 1

PART I2

In yesterday evening's address 3 an attempt was made to present tc
you a general picture of the significance of nematodes as part of the
biological component of the soil. During today's presentation, in ac-
cordance with your request, I shall try to give a review of nematode
forms and types that are considered of importance to the grower because
of a direct or indirect relationship to crop production.
For some decades nematologists have emphasized the presence of
enormous numbers of nematodes in our crop lands and have singled
out many species which are plant parasites or plant pathogens and
therefore of significance to plant growth and crop production. But only
during recent years has an increasing realization of the economic signifi-
cance of plant nematodes as pests of crops, and as limiting factors in
crop production been developed by growers and research workers. Tha:
this disregard of nematodes as a factor in soil response has had its
serious consequences in research, particularly in soil science, may be
illustrated by the fact that various extensive fertilizer tests made in
Florida have had to be repeated because of their insidious damage. It
is obvious that test crops having diseased and parasitized root systems
will not respond in the same manner as would those with normal and
healthy roots. The soil scientist should therefore be aware of the modi-
fying effect nematodes may have on the results of his studies with
fertilizers, cover crops, trace elements, etc.
For years the opinion was prevalent that there was just one significant
nemic plant pest, the root-knot nematode, and it was spoken of as "the
nematode." Although this root-knot nematode is recognized the world
over as one of the worst and most perplexing agricultural pests it is
certainly not the only significant one. There are many other important
plant nematodes such as the meadow nematodes (a group of forms be-
longing to the genus Pratylenchus Filipjev), the spiral nematodes (Genus
Helicotylenchus Steiner),4 the kidney-shaped nematode (Genus Rotylen-
chulus Linford), the lance nematodes (Genus Hoplolaimus v. Daday), the
puncturing nematodes (Genus Dolichodorus Cobb), the stylet nematodes
(Genus Tylenchorhynchus Cobb), the ring nematodes (Subfamily Cri-
conematinae Chitwood), the pin nematodes (Genus Paratylenchus Mico-
letzky), the seed gall nematodes (Genus Anguina Scopoli), to which
SPrincipal Nematologist, Bureau of Plant Industry, Soils and Agricultural
Engineering, U. S. Dept. of Agriculture.
2 Part II, dealing with nematodes affecting the aerial parts of plants is in
process of preparation.
SNematodes and the life association of the soil, p. 7, this volume.
4Steiner, G., 1945: Helicotylenchus, a new genus of plant-parasitic nematodes
and its relationship to Rotylenchus Filipjev. Proc. Helminthological Soc. Washing-
ton. Vol. 12, 34-38, fig. 1A-F.





PLANT NEMATODES THE GROWER SHOULD KNOW 3

belongs, e.g., the wheat nematode (A. tritici [Steinbuch] Filipjev), the
bulb and stem nematodes (Genus Ditylenchus Filipjev), which represent
a group of different species including, e.g., also the rice nematode
(Ditylenchus angustus [Butler] Filipjev), the potato rot nematode
(Ditylenchus destructor Thorne), the sugar-beet nematode (Heterodera
schachtii Schmidt), the golden nematode of potatoes (H. rostochiensis
Wollenweber), the citrus nematode (Genus Tylenchulus Cobb), the bud
and leaf nematodes (certain species of Aphelenchoides Fischer, such as
the fern nematode, A. olesistus Ritzema Bos; the cocopalm nematode,
A. cocophilus Cobb; the strawberry nematode, A. fragariae Ritzema Bos,
causing spring dwarf in strawberry plants; Bessey's strawberry nematode,
A. besseyi Christie, causing summer dwarf; the chrysanthemum nematode,
A. ritzema-bosi), the needle nematodes (Genus Xiphinema Cobb), and
certain spear nematodes of the Genera Dorylaimus Bastian, Pungentus
Thorne and others. There are known today several hundred different
species of nematodes that attack plants and at least a dozen must be
considered major pests while others will undoubtedly be considered as
such after they are better known. In general, however, their significance
as pests is certainly underestimated. There are several reasons for
this. One is the soil-borne character of all plant nematodes; a sec-
ond, their small microscopic size; a third, their hidden mode of life
either in the soil or inside the plant tissues; a fourth, that their
study is technically very difficult; a fifth, that they are considered a
border subject not properly belonging to the field of the entomologist
or that of the plant pathologist or the parasitologist. In addition plant
nematology and its related subject-soil, freshwater, and marine nema-
tology-are not given as courses in our colleges and universities and
are considered only a side line of research by most agricultural institu-
tions.
Then, too, there is the tendency on the part of growers and investi-
gators to judge the health and growth conditions of plants mainly on
the basis of the appearance of the above-ground parts. This generally
leads to an underestimation of the significance of nematodes in their
role as plant pathogens and their influence on plant growth. Since the
roots and other underground parts of plants are the principal portions
attacked by nematodes, a full evaluation of their damage naturally
necessitates the uprooting of a sufficient number of plants for inspection
of the root system. This, of course, often means the loss of many plants.
In the case of shrubs and trees this may involve a considerable loss
without the gain of more than a chance result. The evaluation of the
significance of other underground pests and diseases of crops, as in the
case of plant nematodes, is also more difficult than that of those found
above ground.
Growers frequently are also inclined to blame reduced yields on a
lack of soil fertility, on deficiencies of certain elements, on drought and
other seasonal conditions, on winter kill, sunburn, lightning, and other
factors, when actually nematodes may be the cause of these conditions.
Growers also sometimes tell of the wonderful crops they or their parents
used to grow and that the production of such crops is no longer possible,
even with heavy applications of fertilizers. We are convinced that many





4 DEPARTMENT OF AGRICULTURE

such instances not infrequently would prove upon examination to be the
result of root destruction by nematodes. In other countries the term
"sick soil" is sometimes used to express failure of a given soil to con-
tinue to produce, notwithstanding fertilizer applications or the use of
other means to induce increased production. Nematodes were repeatedly
found to cause such conditions, often more specifically termed by growers
as "alfalfa sick soil," "clover sick soil", "soil tired of beets", "tired of
potatoes", etc.
It is agreed that with our monoculture, that is a single identical crop
planted over wide areas not infrequently year after year or at least, in
close succession, pests and diseases of such crops are provided with
favorable conditions for development. They therefore increase tremen-
dously, particularly in the absence of any natural checks. But here
again in our attempts to look for and control pests and diseases, the
above-ground parts of our crops have attracted most of our attention
and consumed most of our efforts. This has led to modern pest control
of these aerial parts by spraying and dusting practices and by fumiga-
tion. A great deal of research work has been and still is being done
in this connection. However, the root systems and other underground
parts of plants have not gotten their share of attention although soil-
borne pests and diseases, particularly our plant nematodes, are equally
favored by our monocultures.
Fortunately plant nematodes are slow in their spread and are usually
not of such a lethal virulence as many of the fungous, bacterial, and
virous diseases. An outright killing may be effected on seedlings but
this is rather an exception on fully grown plants. Nematode diseases
cause a reduction in growth and vitality, but generally are not completely
lethal. Thus it would appear that, in general, the host-parasite relation-
ship between plants and nematodes is a highly balanced one, that is,
the parasite does not at once kill the host and so deprive itself of a
means of existence. This situation has made these pests appear less
impressive and thus has been another reason for the under-estimation
of their importance.
It is also a fact that many of these pathogenic nematodes, more or
less unconsciously, have been kept under control to some degree by
certain agricultural practices. Plowing, discing, harrowing, and cultiva-
tion are some of the operations that help and are not to be under-esti-
mated as a means of reducing noxious nematodes in the soil. This is
accomplished by exposing the nematodes to the sun, to drying by wind,
to starvation by depriving them of a living host, to mechanical injury,
etc. Crop rotation also has long been recognized as an extremely helpful
agricultural practice through the tendency to reduce the nematode popu-
lation by starvation providing, of course, that one or more crops used
in the rotations are not a host of the particular nematode or nematodes
present in a given soil. Thus various agricultural practices, to some
extent, have been effecting a certain amount of control over soil-borne
nematode pests of plants, but also have assisted in delaying a proper
appraisal of their importance.
This situation began to change with the coming of soil sterilization
by steam and other means including the use of efficacious soil fumigants.






PLANT NEMATODES THE GROWER SHOULD KNOW 5

The efficient control of root-parasitic nematodes and other biotic factors
antagonistic to plant growth through these methods usually results in
remarkable increases in plant growth; the higher yields thus proving quite
conclusively the really detrimental effect of nematodes on crop produc-
tion. But here again, past and current conceptions have been slow to
acknowledge the beneficial effects as being mainly the result of parasite
and disease control.
That the sterilization of soil by steam makes for better growth of
plants, frequently to such an extent that fertilizer applications may be
omitted, has long been known. For an explanation of this phenomenon
it was assumed, however, that such sterilization made more nitrogen
available and that this condition rather than parasite and disease control,
was responsible for the growth and yield increase. With the advent
of efficacious soil fumigants such as carbon bisulphide (CS2), chloro-
picrin (C Cl3NO2), methyl bromide (CH3Br.) and others, including the
most recent DD mixture (1.3 Dichloro-propylene-[CHC1=CH-CH2C1]
Dichloropropane- [CH2Cl-CHCl-CH3]), the same explanation was still
promulgated. Here too, an increase of available nitrogen was assumed
and thought to cause growth "stimulation." Peculiarly enough the
question of where this nitrogen originated, particularly with fumigants
not containing it, did not arise. It was argued that both steam and
chemical sterilization will kill most, if not all organisms in the soil, and
thus make more nitrogen available through the decomposition of the
bodies of these organisms. Such an argument appears fallacious. If
it were correct, then man too would have his living space affected only
through decomposition of his body after death. Life is action and it is,
the living biological factor in the soil that exerts the more extended, the
more intensive, and the more significant action on plant growth rather
than the dead one. That is to say it is the living plant-parasitic and
plant-pathogenic biotic factors in a given soil which are responsible for
reducing the growth and production of crops growing therein. We are
convinced that the striking increases in growth and yield that frequently
follow sterilization, either by steam, hot water, or fumigants, are largely
the result of parasite and disease control and, more particularly, nema-
tode control. The results of soil fumigation in our opinion thus empha-
size the very great importance of plant-parasitic nematodes in crop
production.
Thus the growing recognition of the significance of plant and soil
nematodes as a factor in crop production is well founded. It is hoped
that it will lead to helpful developments for the control of these crop-
antagonistic biotic factors through the use of more efficacious fumigants,
and better methods of application. Here the way is open for significant
increases in crop production combined with a possible reduction of
acreage and a lessor need for fertilizers. Let us provide healthy root
systems for our crop plants through control of the many nematodes and
other agents now causing root lesions, root decay, root amputations,
blind root tips, abnormal matted growth, etc., and surprising yield in-
creases will result. A healthy root system will more effectively utilize a
lower fertility level in a soil or take more advantage of one that has been






6 DEPARTMENT OF AGRICULTURE


artificially increased
affected by disease.


by fertilizer applications, than will one that is


Figure 1.-Roots of a tobacco plant grown in South Carolina and disfigured
through a heavy infection by the root-knot nematode. Note the stunted, blinded
and swollen roots and compare with type of root disfiguration and galling shown
in Figure 2. Such variations in character of root galling and disfiguration may
be related to different root-knot nematode strains or races, but may also be the
result of different reactions by the hosts.?

How are the growers to recognize the presence of these microscopic
nematode pests on their crops, and how are they to know the kinds in-
volved? Are there specific symptoms which indicate that a disease or
abnormal behavior is caused by a nematode, or an association of nema-
todes, or a combination of nematodes and fungi or bacteria, or a combi-
nation of all three of them, or a combination of still some other factor
or group of factors with nematodes? Unfortunately there exists only
one sure way to determine this, namely the location and identification
of the nematodes themselves. May we therefore emphasize that it is not
possible to recognize and properly diagnose nematode diseases of plants
1 Most of the photographs used to illustrate the present paper were taken by
Mr. Marcel L. F. Faubert of the office of Plant and Operations; others by Mr.
Wilfred T. Mead of the Bureau of Plant Industry, Soils and Agricultural Engineering.
The author wishes to express to both of them his appreciation for the excellent
service.





PLANT NEMATODES THE GROWER SHOULD KNOW 7

by symptoms alone; in every instance the nematode itself should be
located and determined before a final diagnosis is made. Let us support
this statement by an example. It is widely assumed that the root-knot
nematode may be correctly recognized and properly diagnosed through
the symptoms it causes on the roots of its host plants, namely conspicu-
ous swellings, knots or galls. (Figs. 1-8) But even in this instance it
is fallacious; such symptoms are only indicative but certainly not proof
of an infection by the root-knot nematode because: (1) there are knot-
forming nematodes found on roots of plants other than the root-knot
nematode (e.g. Ditylenchus radicicola [Greeff] Filipjev, or Nacobbus
dorsalis Thorne & Allen), (2) the root-knot nematode may be present
without causing the formation of knots (this is often seen, e.g., in cotton
or corn where the nematode breaks through the surface of a root without
forming knots) and roots are then mistakenly judged free, (3) other
organisms may form similar knots, e.g. the slime molds (Plasmodiophora
species) causing clubroots in members of the cabbage family, the crown
gall organism (Bacterium tumefaciens Sm. & Town) and certain viruses;


Figure 2.-Roots and pods of a peanut plant (Arachis hypogaea L.) infected
with the root-knot nematode which formed only small galls on the roots but blackish
lesions on the pods. This attack at the ends of pods causes interruption of growth
and misshapen and often dwarfed pods.








































































Figure 3.-Seedlings of one of the rubber-producing dandelions (Taraxacum kok-
saghyz Rod.) exhibiting root swellings caused by the root-knot nematode.


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PLANT NEMATODES THE GROWER SHOULD KNOW 9


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Figure 4.-A. Heavily knotted and crippled roots of a Laredo soybean plant
grown in Virginia infected with the root-knot nematode; % normal size. B. Heavily
knotted and crippled roots of a young Castilla elastica Cerv.; % normal size.
knotted and crippled roots of a young Castilla elastica Cerv.; 3 normal size.


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Figure 5.-A. Roots of black locust seedlings (Robinia pseudoacacia L.)
damaged by the root-knot nematode. Note the swollen and blinded root tips; 3%A
normal size. B. Roots of a daylily (Hemerocallis hybrid) infected with the
root-knot nematode. Note again the blinded root tips; otherwise the knots and
galls are only slightly noticeable on the fleshy roots; % normal size





PLANT NEMATODES THE GROWER SHOULD KNOW


also so-called bacterial nodules may be mistaken for root-knot galls,
but they usually are easily distinguished from knots caused by the
root-knot nematode by the fact that they are mostly fixed on a short
peduncle and hang on the side of a root whereas the swelling caused
by the root-knot nematode is most often an axial one of the root proper
(Fig. 9), (4) there are certain plants that have normally knotted or
swollen roots (e.g. Parthenocissus sp.). Thus it is evident that even this
common root-knot nematode disease must be diagnosed by the presence
of the organism itself rather than through the occurrence of knots of one
kind or another on the roots.




















A C


















Figure 6.-A. Root-knot infected sweetpotatoes; the sweetpotato to the left
exhibits cracking which appears to result in certain instances from a root-knot
infection. B. Beet heavily infected and disfigured by the root-knot nematode. C.
Carrot disfigured and made unmarketable by the root-knot nematode; 2 normal size.
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exhbis rakig hih ppar t rsut n erai istncs ro arot-no
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11















































































D .
Figure 7.--A. Bliss triumph potato badly infected and disfigured by the root-
knot nematode. Specimens collected at Gainesville, Florida. Note the protruding
knobs formed by the nematode and compare with B where symptoms are sunken,
crater-like spots. B-E. Bliss triumph potato infected and disfigured by the root-knot
nematode. Specimens collected at Tampa, Florida. It is thought that the difference
in symptoms observed in the potatoes of A and B-E of this Figure are the result of
racial differences in the attacking nematode nonulations: 2 normal size.
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racial differences in the attacking: nematode -Doiulations: 2/nnormal size,





PLANT NEMATODES THE GROWER SHOULD KNOW 13

Furthermore, for a proper assay of the status of a given plant as a
host, it should be ascertained whether the nematode is actually producing
progeny on it. For a demonstration of this point the root-knot nematode
may serve again. Our observations appear to show that the pre-parasitic
larvae of this form enter the roots or subterraneous stem and leaf for-
mations of almost any type of plant in spite of the fact that, in most















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A B C D

Figure 8.-A. Root-knot infected bean seedling with galls also on the leaves
(at arrow). B. Root-knot infected bean seedling with galls also on the stem
(at arrow). C & D. Malformed and dying bean seedlings with heavy infection of
the root-knot nematode; 1/2 normal size. Attention may be called to the fact that
such heavy invasions of seedlings, leading to the ultimate death of the plants before
the invading nematodes have time to produce progeny, may lead to such a reduction
in the number of nematodes that a replanting with beans may be fully successful.

cases, they are unable to develop in them and to produce progeny. In 1937
it was found that the root tips of French marigolds (Tagetes hybrids)
were heavily invaded by larval root-knot nematodes, while galls with
fullgrown females producing egg masses were observed in only small
numbers. Upon closer study it was shown that most of the larval nema-
todes that invaded these roots were unable to develop to the adult stage
and died before reaching it. Obviously these resistant marigolds did not
furnish the invading root-knot larvae with the proper food, or the nema-








DEPARTMENT OF AGRICULTURE


tode larvae did not have the ability to induce the invaded host to produce
their food. Further studies on so-called resistant plants showed a similar
situation to exist, e.g. in Crotalaria spectabilis Roth, Solanum grandiflorum
R. & P., lantana (Lantana camera L.), "dusty miller" or silver cineraria
(Senecio cineraria DC.), Nicotiana megalosiphon Huerck & Muell. Arg.
and Nicotiana plumbaginifolia Viv. Crotalaria spectabilis proved to be


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Figure 9.-Lespedeza stipulacea Maxim., Korean clover, showing nodules caused
by the root-knot nematode (solid arrows), and nodules caused by beneficial
nitrogen-fixing bacteria (open arrows). Coll: Virginia, 1941; % normal size. It
may be mentioned that this lespedeza is an excellent indicator plant to detect the
presence of the root-knot nematode in the soil. Where this nematode occurs in a
soil growing this species, the plants always will be stunted and yellow.


14


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PLANT NEMATODES THE GROWER SHOULD KNOW


one of the most interesting plants yet studied in its host-parasite relation-
ship with the root-knot nematode. It was observed that the root tips of
growing specimens are invaded by large numbers of larval root-knot
nematodes, but up to the present time not one larva has ever been found
to have reached the adult stage. They all appear to perish at a very
early stage of fixation in the root. This legume is therefore an excellent
trap plant and cover crop combined. On the basis of greenhouse and
field experiments it has been found very effective in cleaning infested
land of the root-knot nematode. In entering the roots the nematode
appears to be able to induce the root tissues to produce the so-called
giant or nectarial cells on which it feeds, but for some reason the nema-
tode will not grow to the adult stage and produce eggs and progeny.
However, even in this case the plant suffers from an invasion of its roots
by these nematode larvae; this is shown by the fact that small seedlings
of C. spectabilis will die or at least appear sick for a time after invasion.
Eventually the plant will recover. Solanum grandiflorum R. & P., a
weed growing in Brazil 5 and used there as a root stock for tomato grafts
on root-knot-infested lands, exhibits characteristics quite similar to those
of Crotalaria spectabilis in its relationship to the root-knot nematode.
Here, too, the roots are invaded and their tips blinded by the larval
root-knot nematode which again is unable to grow and develop as it
becomes fixed. This Solanum eventually will also attract from the soil
larval specimens of the nematode but will recover after their invasion
and death. Here again the young seedlings may suffer badly from this
invasion and, in fact, may even be killed. Of a total of 100 seeds
planted in root-knot-infested soil only three seedlings survived while a
control planting from the same lot of seed in sterilized soil gave full
germination and only healthy growth.
Still another variation in host-parasite relationship is shown by the
rose geranium (Pelargonium graveolens [Thumb] L'Herit). In this
plant the roots also appear to possess considerable resistance against
attack. Few galls are formed, many of which are empty, and only oc-
casional ones were observed with egg-laying females. In contrast to this
behavior of the roots, the basal portion of the stem appears to be very
attractive to the root-knot nematode and consequently is invaded by large
numbers, galls being formed and female specimens being able to grow
to maturity and produce eggs (Fig. 10).
We are convinced that a study of the numerous host plants affected
by the root-knot nematode, including the so-called resistant and immune
types, will bring to light additional information of much value for a
better understanding of these numerous and complex host-parasite inter-
relationship. These are all matters of not only theoretical interest, but
of great practical importance since they find their application in control
through effective crop rotations.
There are still other complicating factors that make the diagnosis of
root-knot infections and a proper appreciation of their significance diffi-
cult. Observations on the host range of this nematode in different regions
and locations, as well as studies on the resistance of an identical crop
SFor the opportunity of studying this plant we are indebted to S. B. Fenne
of the Institute of Inter-American Affairs.


15







DEPARTMENT OF AGRICULTURE


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~i~s9~- c~ci


Figure 10.-Roots and basal stem of a rose geranium exhibiting galls (at
arrows) of the root-knot nematode.


16





PLANT NEMATODES THE GROWER SHOULD KNOW 17

variety planted at different locations, have shown that plants and crops
attacked in one location sometimes are not attacked in another. Evidence
is rapidly developing through systematic studies to prove that there exist
different host strains or host races of this nematode, each of which has
its own host range; some regions or localities appear to have only a
single strain, whereas in others two or more occur, often in a mixed
state. A similar situation appears to exist in other nematode species,
for example, the bulb and stem nematode or certain bud and leaf nema-
todes (Aphelenchidae species). These matters are mentioned to empha-
size the fact that the diagnosis of a nematode infection and the evaluation
of its capacity for damage must be made with care and knowledge.
Disease symptoms produced by the various species are rarely specific;
wilting, discoloration of leaves, swollen and distorted shoots, crinkled
leaves, leaf spots, gall formation on roots, stems and leaves, galled fruits
and seeds, bunching and dwarfing of the entire plant, blinding of buds,
and the phenomena termed dieback, sunburn, winter kill and winter
bronzing may be caused by nematodes. General wilting of plants in the
field over a hot period of the day may be indicative of the presence of
large numbers of root nematodes, as may also bare spots or areas ex-
hibiting retarded or reduced growth. However, all of these symptoms
likewise may be caused by various other organisms and agents. Again,
therefore, external symptoms alone can not serve as a reliable basis for
the diagnosis of a nemic plant disease. The identification of the organism
is absolutely necessary.
Nematodes, or eelworms, so far as plant-parasitic forms are con-
cerned, are very small animals, less than 2 mm long, usually only from
0.4 to 1 mm (or 1/64 to 1/25 of an inch). Therefore they can not be
seen with the naked eye and must be studied with the microscope. Al-
though of such small size, their organization is highly complex and
embraces all organs and organ-systems found in higher animals except
a circulatory system. It is difficult for the untrained worker to differ-
entiate the various genera and species and some of the thousands of
soil-inhabiting forms may easily be mistaken for those which are defi-
nitely parasitic to plants. The grower and entomologist as well as the
plant pathologist should keep this in mind and if there is any doubt
regarding the symptoms, an identification should be requested from a
nematologist. Considering the comparative youthfulness of this branch
of science, it should be remembered that even the specialists' views
concerning the relative significance of these forms are subject to a great
deal of change and modification.
It has already been pointed out that nematodes constitute an ex-
tremely large and varied group of animals, divided into many different
families. With some exceptions, the plant-parasitic forms belong to only
three of these families; the Tylenchidae, the Aphelenchidae, and the
Dorylaimidae. The members of all three of these families are provided
with a stylet with which they feed. This organ appears to be fully
effective in puncturing the plant tissues; and in obtaining the food re-
quired by these parasites by sucking. Furthermore, many types of plant-
parasitic nematodes appear to induce the host plant to produce their
particular food requirements by injecting into the plant tissues the





B


odon to-stylet...


Tylenchidae Aphelenchidae Dorglaimidae
I... 2


stomato-stylet

stylet a transformed
buccal capity


odonto-stylet

stylet a
transformed toof t


Figure 11.-Schematic drawings to explain the main differentiating characters
of the three groups of nematodes to which most plant-parasitic forms belong. A.
Tylenchidae, B. Aphelenchidae, C. Dorylaimidae. dsl oes gl, dorsal oesophageal
gland; int, intestine; mdl bib, middle oesophageal bulb; nrv r, nerve ring; out dsl
oes gl, outlet of dorsal oesophageal gland; out rt subv oes gl, outlet of right sub-
ventral oesophageal gland; rt subv oes gl, right subventral oesophageal gland.


A





PLANT NEMATODES THE GROWER SHOULD KNOW


secretions of their large esophageal or salivary glands. For this purpose
the stylet is used as an injecting needle.
The stylet of the tylenchs and also that of the aphelenchs is called
a buccal stylet or "stomato-stylet". It is assumed to have originated
through the transformation of the buccal cavity of the ancestors of these
two closely related families. The sclerotized walls of the buccal cavity
of these ancestors are assumed to have been amalgamated and so to
have formed a perforated tube, or the buccal stylet presently seen in
these forms. (Figs. 11 & 12). In the dorylaimids, however, which repre-
sent a group of very different origin and relationship, the stylet is
assumed to be a transformed tooth and is therefore termed an "odonto-
stylet." (Fig. 13).

































Figure 12.-Drawings of various developmental stages of the root-knot nematode.
A. Unsegmented egg; B. egg, containing larva; C. migratory larva free in the soil;
D. sausage-shaped larva living sedentary in the root; E. larval molt containing
fully developed male; F. adult male; G. young female. X 140
F A B C E


19








J'


Si-

-4. . ..















Ea..,
-_- P












Figure 13.-Photomicrographs of developing larvae of the root-knot nematode
in roots of balsam (Impatiens balsamina L.) A. Swollen portion of a root with
numerous larval nematodes arranged around its axial cylinder (X 25); B. single
young larva, its body only slightly swollen but the root tissue cells around its head
end already enlarged to form the so-called giant or nectarial cells. The immigrating
root-knot nematode larva in settling down for its permanent, life-long location injects
secretions of its oesophageal glands into the root tissue. These injections stimulate
the cells to increased growth and, by secretion, to the production of a type of fluid
food which is directly assimilable by the host. It appears that this food material is of
such comparatively simple structure that a regular digestion in the intestine of the
parasite is not further necessary. The intestine of these parasites appears to be
mainly a storage organ for food reserves and the rectum and anus are often vestigial
(X 63); C. same as B but a later stage (X 100); D. same as B and C but
still a more advanced stage than C. The molt of the larva is seen as a faint
mark surrounding its body (X 100).






PLANT NEMATODES THE GROWER SHOULD KNOW


The tylenchs and aphelenchs include the most outstanding plant
nematode pests, many species of which often occur in very large numbers.
The two families are differentiated mainly by one character. In the
tylenchs the dorsal esophageal or salivary gland empties into the alimen-
tary tract a short distance behind the buccal stylet (Fig. 11), while in
the aphelenchs it empties into this tract in the middle esophageal bulb
just in front of its valvulae (Fig. 12).
The dorylaims occur in numerous genera and species in soils every-
where. Many live parasitically on and in plants, even in the leaves and
other above-ground parts, but they rarely occur in such great numbers
in an attacked plant as do certain parasitic aphelenchs and tylenchs. All
dorylaims appear to lead a migratory mode of life although some occur
in plant tissues apparently quite sedentary, their body rolled up in a
more or less tight spiral.
The most prominent characteristics of the tylenchs and aphelenchs,
in comparing them with dorylaims, is their decidedly greater size and
the more highly developed function of their oesophageal glands. These
characteristics doubtless are directly related to the much more pro-
nounced pathogenicity of the group. For instance, in many species of
tylenchs and aphelenchs, the secretions of these glands are known to
have a poisonous effect on the host in addition to inducing the host
tissues to produce directly assimilable fluid for use as food by the para-
site. The presence of these enlarged and strongly functional oesophageal
glands in the tylenchs and aphelenchs appears, in general, to indicate
an extra-oral digestion and, correlated with it, a transformation of the
intestine into an organ designed mainly for storage of food reserves.
It is on this account that they are able to feed by inducing the host
tissues, through glandular injections, to produce directly assimilable
food. The dorylaims, on the other hand, suck the cell contents directly
from the host tissues; these cell contents, in turn, are digested and broken
down to simple assimilable forms of food in their intestine.
In reviewing the more important plant-parasitic nematodes, it appears
best to begin with those types capable of attacking the growing roots
of plants. Certain species, of course, are of far greater economic im-
portance than others. It is with these species that we will first deal.

THE ROOT-KNOT NEMATODE
The root-knot nematode (Heterodera marioni [Cornu] Goodey) is
considered the most important of this group. Its extended distribution
through the tropics, subtropics, and temperate regions and its occurrence
in greenhouses everywhere, make it one of the most widely distributed
and common agricultural pests. It has long been known in Florida.
Neal states that the disease, as such, was known to occur here as early
as 1805, although the causitive organism, the nematode, was not dis-
covered until 1879, and was first definitely established as occurring in
Florida in 1889. While it doubtless is now present in all sections of
the State it is particularly bad in those areas where sandy and peaty
soils prevail, where it causes damage in various ways that may well be
estimated at several million dollars annually. It also has been reported


21






DEPARTMENT OF AGRICULTURE


to occur in almost every State of the Continental U. S. A. Although this
organism was formerly thought incapable of surviving the winter in the
northern part of our country, this is a misconception, for experiments
and observations show it is fully capable of withstanding extreme cold
when in the soil, and of surviving temperatures as low as 10F. if ex-
posed. Root-knot does not cause such extensive damage farther north,
however, as it produces under warmer climatic conditions, apparently
because northern summers are short and cool, thus preventing the de-
velopment of more than one or two generations.
In the description of the life cycle of the root-knot nematode we
may best begin with the preparasitic larva (Fig. 12C) after it has
hatched from the egg (Fig. 12 A & B) and migrated through the soil
until it has reached a root tip, where it makes its entry. After migrating
to the axial cylinder of the root, it becomes sedentary, (Fig. 12A) and,
with its short buccal stylet, injects the secretion of its oesophageal or
salivary glands into the tissue of the roots. Thereupon the cells of the
root begin to form from three to five so-called giant cells at the injection
point around the oral opening of the nematode (Fig. 13 B-D). These
cells are also called nectarial cells from which the nematode absorbs its
food during its entire life. With the intake of food the larva begins to
swell rapidly, first becoming sausage-shaped (Figs. 12 D and 13 B-D)
and then growing to a pear-shaped, whitish body (Figs. 14, 15 & 16).
At this stage of development it may be so large in some instances that
it can be seen with the naked eye (Fig. 17). Under favorable conditions
this development may take three to four weeks, but a much longer time
is often required, particularly when the temperature is suboptimal. The
full-grown female produces eggs (Fig. 18 B) which are deposited in a
yellowish-brown, jelly-like substance which flows from the female genital
opening prior to egg production (Figs. 14 & 16). The number of eggs pro-
duced varies a great deal. The average is considered to be 400 to 500, but
this number may be much smaller or considerably larger since over
2,000 eggs have been observed to be produced by a single female. This
variation in the number of eggs is caused not only by temperature con-
ditions, but also by the kind of host, some plants being more suitable
than others. Each egg may develop a larva (Fig. 12 A & B), which
will break the eggshell and become free in the soil by the cracking of
the root or at the time of its decay. The egg stage is unquestionably the
most resistant, and it is in this stage that the nematode may survive long
periods of adverse conditions. A larva free in the soil succumbs quickly
to adverse conditions such as lack of moisture, excessive heat, direct
sunlight, or cold. Males develop under certain conditions but they ap-
pear to play no role in the production of progeny. They are slender,
eel-like organisms of very different shape from the females (Fig. 12
E & F). Their development is very interesting; instead of growing
to a pear shape like the females, a male larva at the sausage-shaped
stage is transformed into a threadlike, cylindrical nematode folded and
wound up inside the larval molt from which it finally escapes as a
mature male.


22






PLANT NEMATODES THE GROWER SHOULD KNOW


Figure 14.-Drawing of an adult female of the root-knot nematode with
attached egg mass embedded in a protective jelly. X 115


23






DEPARTMENT OF AGRICULTURE


Figure 15.-Photomicrograph of a swollen root section of the balsam plant
(Impatiens balsamina) with numerous adult females of the root-knot nematode;
the eggs of one specimen can be clearly seen. X 50


24


.i
,,






PLANT NEMATODES THE GROWER SHOULD KNOW


It is evident that during its life cycle the root-knot nematode passes
a prolonged period inside the host plant, possibly from three to five
months. The egg and the migratory larvae are the only stages that may
normally occur free in the soil. In control procedures this is an im-
portant point. Fumigants applied to the soil sometimes reach only
larvae and eggs free in the soil, while specimens inside a root, particu-
larly if it is woody, may not be affected. The complete uprooting of
plants will eliminate all stages inside the roots-eggs, larvae, and
adults-if the roots are destroyed. The development of the larvae is
interrupted if the root on which they are feeding is disturbed, and they


.--r" :"** : -

































Figure 16.-Photomicrograph of two adult female root-knot nematodes in a
balsam plant root (Impatiens balsamina); the giant or nectarial cells are seen as
darkened cell masses in the axial cylinder of the root; the jelly mass secreted by
the females is seen surrounding the broad posterior end of the females, the pointed
head end of which is embedded in (upper specimen) or directed toward (lower
specimen) the giant or nectarial cells. X 135
... .~ s ,., .....ss~s8sB~si~Egil











head end of whihi"ebde n(pe pcmn rdrce oad(oe

spcmn h in rn3ailcls 3


25








DEPARTMENT OF AGRICULTURE


will perish when the root dies. In fleshy roots, however, such as peony,
and in rhizomes, corms, tubers, and bulbs development may go on, if
these plant parts are stored or otherwise kept under conditions favorable
to the nematode. This situation explains the many opportunities for the
distribution of this pest through infected plant material as, for example,
nursery stock and root crops such as potatoes, carrots, etc. The spread
of the larvae by active migration is slow.
Over 1700 different plant species are known to be attacked by the
root-knot nematode. However, they exhibit a wide variation in the


Figure 17.-Photomicrograph of female root-knot nematodes embedded in the
tissue of a potato of which a thin surface portion was sliced off. In potatoes
these adult females may often be recognized with the naked eye. X 3


26


ii
-i


i;


--~i t-
..--I




,
alt -75--
-~
I :.
16 DI-

,-8Z ;;

~t~
..
.-
:i


~~~~"~~ Q








PLANT NEMATODES THE GROWER SHOULD KNOW


. :


B


Figure 18.-A. Photomicrograph of a larval specimen of the root-knot nematode
in the tissue of the same potato shown in Figure 17. B. Photomicrograph of an
egg mass of the root-knot nematode in the tissue of the same potato as shown in
Figure 17. X 85


27


i

ne
(~'(' ~
,. Y


"'
_'ps~

P

12:





DEPARTMENT OF AGRICULTURE


degree of susceptibility to attack and in the seriousness of the disease
that follows. Thus some suffer severely from a slight attack (e.g.
cyclamen) while other species are very tolerant (e.g. mulberry tree).
It should be mentioned here that germinating seeds and young seedlings
are particularly attractive to the root-knot nematode larvae (Fig. 8)
including even seedlings of plants otherwise immune or highly resistant.
Seeds should therefore never be planted in soil badly infested by the
root-knot nematode or by any other plant-pathogenic nematode form,
nor should such soil be used for seed-testing purposes. Germination will
be poor and most of the emerging seedlings will be sickly. Thus the
seedlings of the tung oil tree (Aleurites fordii Hemsl.) are very suscep-
tible and may die from an early infection but after the first year may
recover and then develop a high degree of resistance.
It was mentioned earlier that in some plants the root-knot nematode
breaks through the root surface so that the egg-producing females pro-
trude from the root and may then be seen with a hand lens as globular,
whitish bodies with yellowish or brownish egg masses attached. Some-
times not even swellings are formed. Under such conditions the parasite
is even more injurious than in those cases where a smooth, uncracked
gall without necrotic tissues is formed. This is due to the fact that roots
cracked or opened by the action of this nematode are at once invaded
by a whole group of secondary agents including other nematodes, fungi,
and bacteria and this usually leads to quick decay. Plants thus attacked
naturally suffer much more than those which form "smooth," uncracked
or, if such an expression is permitted, "healthy" galls.
Frequently growers or scientific workers looking for this nematode
with the conception that galls or knots are its symptoms, have often
considered the nematode absent because there were no galls. Thus they
have missed the root decay initiated by this nematode which is usually
much more serious than the galls.

SEDENTARY TYPES
This leads us to other sedentary types of plant-parasitic nematodes
of roots, namely the sugar-beet nematode and related species like the
golden nematode of potatoes. In these species even the growing larvae
normally protrude from the root surface and the adult females generally
hang on the outside of a root. In contrast with the root-knot nematode,
the members of the sugar-beet nematode group have a characteristic
which makes their control much more difficult. The old females, before
dropping from the root or tuber, turn from a whitish color to brown as
their cuticle is transformed into a thick, protective cover with a variable
number of eggs and larvae contained inside. Females thus transformed
are then called "cysts" and may remain in the soil for years, releasing
active larvae over a period of years. This phenomenon not only compli-
cates control of these pests when crop rotation schemes are used but
also when fumigants are used, since these "cysts" are highly resistant
to the action of chemicals. We know of no species of this group occur-
ring in Florida but are convinced that at least one form, Heterodera


28






PLANT NEMATODES THE GROWER SHOULD KNOW


weissi, n. sp.6 (Fig. 19) may be present. It is found on various species
of knotweeds and is known to us to occur in numerous states east of the
Rocky Mountains, as far south as the Delta section of southern Missouri
and the region of Ridgeville, Georgia.


Figure 19.-A. Male of Heterodera weissi n. sp., the knotweed heterodera,
located under the surface of a root of Polygonum pensylvanicum L. B. Female
Heterodera weissi n. sp., as it hangs on a root of the same knotweed as above;
X 100.

The root-knot nematode, together with the various species of the
sugar-beet nematode group, represent sedentary root parasites which are
SDiagnosis: Heterodera with small, lemon-shaped cysts (330 to 404a X 590
to 617g) with protuberant vulva; outside surface of cyst wall with network of
transverse, meandering and anastomosing ridges, separating depressions which are
mostly elongate, somewhat rhomboidal in shape. Male 1.010-1.34 mm, with annu-
lated, well set off, semi-spherical head; buccal stylet of about 28-29u; ventral
terminal anus with protruding lips; spicula 34,u; gubernaculum 10j; a = 35-36;
. = 8.4-11.8; 7 = about 0. Eggs 32 to 42A X 81 to 114u. Preparasitic larvae
0.320 to 0.388 mm, their head with 6 annules. Known to infect the roots of various
species of the genus Polygonum in the United States east of the Rocky Mountains.
Type host: Polygonum pensylvanicum L.; Type locality: Plant Industry Station,
Beltsville, Maryland.


29





DEPARTMENT OF AGRICULTURE


'.root


-. lype of Rn

.pex


Figure 20.-Drawing of a female of the citrus nematode, Tylenchulus semi-
penetrans Cobb, attached to a root. The elongated head end is shown inserted
deep into the root tissue so that the cells of the axial cylinder are reached. p ex,
excretory pore; type of ann, annulation of cubicle, only partly drawn; vlv, vulva.


30
















































O '< o *.. f .,..,






Figure 21.-The kidney-shaped nematode, Rotylenchulus reniformis Linford.
A. Pieces. of roots of Jacquemontia tamnifolia L. Griseb with specimens of the
kidney-shaped nematode attached to them. Their body is covered with small soil
particles which are held together by a glabrous secretion produced by the nematode.
Thus, the uniformed will never suspect that the small globular bodies attached to
these roots are not parts of soil but hide a sedentary root-parasitic nematode.
X 24. Sample collected by A. L. Smith at Cuthbert, Ga. B. Tomato root infected
with the kidney-shaped nematode; the glabrous cover surrounding the nematodes
has been teased off to expose their bodies; their elongated neck, with which they
penetrate the root, may be seen. Tomato plant experimentally infected in a green-
house. X 170.





DEPARTMENT OF AGRICULTURE


all combined in a single genus, all closely related and difficult to differ-
entiate. The adult female has a swollen, spherical, lemon- or pear-shaped
body, unlike most other nematodes, while the male retains a threadlike
body shape.
But this group is not the only one in which sedentary life has re-
sulted in transformation of the female by globular inflation. The same
phenomenon is seen in other genera of quite different origin and rela-
tionship; an outstanding example being Nacobbus, a form only recently
described by Thorne and Allen from California. Here the female has
a protruding vulva of such length that it resembles a tail; this enables
it to deposit the eggs outside the root since the protruding tail-like vulva
appears always so located as to reach the root surface.
\ The citrus nematode (Tylenchulus semipenetrans Cobb) is still an-
other example of a swollen, sedentary type of root parasite. It belongs
to still a different taxonomic group from the two already mentioned. In
this instance the roots are attacked from the surface and only the
elongated anterior portion of the body penetrates the root tissue, while
the posterior part swells, as shown in Fig. 20. Here again, however, the
male is of very different shape and appears not to feed at all. In fact
it hardly increased in size while developing from the larval to the adult
stage.
There is still a fourth type of swollen sedentary root parasitic nema-
tode, the kidney-shaped nematode (Rotylenchulus reniformis Linford).
The parasitic female is attached to the root surface but its body is sur-
rounded by a spherical structure which it forms for itself by secreting
a glabrous substance which also surrounds the eggs and cements together

Figure 22.-Two different types of ring nematodes. A. Criconemoides citri
n.sp.,' representing a broadly annulated type, infecting roots of the sour orange
in the region of Orlando, Fla. The roots are punctured from the surface with
the remarkably strong buccal stylet and the head itself is frequently buried deep
in the root tissue which becomes necrotic around the organism. B. Criconema
civellae n.sp.," representing a very unusual type of nematode with its 8 longitudinal
series of fringed scale-like structures on the body surface. It was found feeding
on the roots of Citrus grandis (L.) Osbeck, the pummelo, grown in a greenhouse
of the Plant Industry Station, Beltsville, Md.

'Diagnosis: Criconemoides resembling C. sphaerocephalum A. L. Taylor but
different because the anastomosis of the annules along the lateral line is simple, i.e.,
the annules do not break joint to form a zigzag suture as in C. sphaerocephalum;
buccal stylet shorter, only 50,a long; middle bulb of oesophagus only about /
width of body cavity; isthmus and terminal bulb much longer than in C. sphaero-
cephalum.
Measurements: Total length of 9 = 0.252mm; a = 8.4; 8 = 2.3; 7" = 31.5
Type host: Citrus aurantium L.; Type locality: Orlando, Florida.
2 Named for Mrs. Civella Adams Chambliss, Scientific Aid in the Division of
Nemptology, U. S. Dept. Agriculture, in recognition of her first finding of various
forms of this group of plant-parasitic nematodes so difficult to locate. The new
species is provisionally placed in the genus Criconema Hoffmanner & Menzel 1914.
Diagnosis: Criconema resembling C. octangulare (Cobb 1914) Taylor 1936 but
different because each scale of the 8 longitudinal series has a fringe of from 4 to
6 stiff, outward- and backward-pointing setae on its posterior edge. Annules
numbering from 58 to 62. Buccal stylet 68g. Total length = 0.376 mm. Type
host: Citrus grandis.


32





PLANT NEMATODES THE GROWER SHOULD KNOW 33

Figure 22





DEPARTMENT OF AGRICULTURE


adjacent soil particles. We located this interesting species recently from
Florida on roots of tomato and coffee weed (Cassia tora L.) sent to us
from Quincy. As in the citrus nematode, the anterior portion of the
body of the female is elongated and is inserted into the root while the
reniform, main part protrudes from the surface. The male in this case
also remains small and its body is not swollen. Because of its bubble-
shaped glabrous enclosures covered with soil particles, Rotylenchulus
is very difficult to see and may easily be overlooked or mistaken for
globular soil agglutinations adhering to the root (Fig. 21).


Figure 23.-A ring nematode (undescribed species) attacking the root of a
pummelo (Citrus grandis) grown in a greenhouse at the Plant Industry Station,
Beltsville, Md. Its head is buried in the root surface; several nearby surface
cavities were probably made by the same nematode; X 75.


34





PLANT NEMATODES THE GROWER SHOULD KNOW


It is obvious that all these sedentary nematodes with inflated and
obese bodies that become fixed in or on a root lose their motility and
are unable to change their position and migrate. If roots containing
such stationary parasites are uprooted and destroyed before the parasites
are fully grown or before they have produced eggs, the source of in-
fection is removed. Control of certain of these nematodes by a trap- or
catch-crop is based on these considerations. Since only the preparasitic,
larval stage of these sedentary forms is able to migrate, the spread of
these various types by their own means is very restricted. Thus long
distance travel is entirely one of transportation by such carriers as wind,
water, and particularly man, who spreads them with plant material of
all kinds and with soil.
There exist other sedentary root parasitic nematodes which in contrast
with the foregoing groups have preserved a certain, though reduced,


N4


Sr
d


/j


Figure 24.-Procriconema sp. attacking the roots of slash pine seedlings (Pinus
caribaea Morelet) near Olustee, Fla. The arrows point to groups of nematodes
attached to blinded root tips; X 25.


35


-- 1
I
aj

















-j /- I, /
--_ ---



Ii 1 -------- --- - -








_.ii._ // i I
(II



lii' I I/1



IN .
ii
j ,






















Figure 25.-Drawing of a spiral nematode (Helicotylenchus sp.) attacking a
rootlet of sweet clover (Melilotus sp.) The anterior end of the nematode has
deeply penetrated the root tissue; dotted region indicates the extent of cell necrosis
evidenced by discoloration; specimen collected by F. R. Jones, Madison, Wis.;
X 333






PLANT NEMATODES THE GROWER SHOULD KNOW


motility; they are called ring and scale nematodes and include various
genera and numerous species belonging to the Criconematinae and other
related groups (Fig. 22 A & B). They too are ecto-parasites, puncturing
the surface of roots (Fig. 23) and other subterraneous parts with their
stylets which are strong and often extremely long. All members of this
group are short and stout and heavily annulated. In some, the annules
are provided with retrorse scales or spines, or a combination of the two.
This annulation and its armature obviously enables the members of these
groups of rather unusual looking nematodes to get the necessary support
and resistance in the soil while they press their stylets and heads into
the plant tissues. Locomotion also is possible mainly through the use of
the annules and their scales and spines. Certain types of these groups
(e.g. Procriconema Micoletzky) are of pronounced, sedentary habit
(Fig. 24). They retain their moulting skins, which make an additional
protection for their bodies while quite permanently attached to a root.
Locomotion of these animals with a double sheath around them would be
extremely difficult.
Finally there are root-surface parasites with well developed locomo-
tive ability which nevertheless pass a sedentary existence on roots for
extended periods. One group of these are the ancestors of the kidney-
shaped nematode previously mentioned. They are forms widely dis-
tributed and because their long body is usually kept in the shape of a
spiral they are called spiral nematodes (e.g. Helicotylenchus Steiner;
Rotylenchus Filipjev). Their buccal stylet is quite long and strong and
well fitted for inserting into plant tissue. Often the head and part of
the anterior portion of the body are also inserted into the root (Fig. 25).
It is thought that this procedure is made easier by the retention of their
bodies in a ventrally curved spiral of one to two turns. These spiral
nematodes are still little known but are of wide distribution. Where
numerous they may seriously interfere with plant growth. Helicotylen-
chus nannus Steiner is a small but very common species in the south-
eastern U. S. A., including Florida.
Of similar behavior are the pin nematodes (genus Paratylenchus
Micoletzky). The body of this genus, particularly that of the female,
is ventrally curved but to a lesser degree than in the spiral nematodes,
possibly because they are much shorter. All members of this group are
unusually small, and for this reason they frequently have been over-
looked. It now appears that they are rather common, sometimes occur-
ring in enormous numbers. The buccal stylet of the various species is
always long, although the length differs considerably. This organ may
be inserted into the plant tissue for a considerable portion of its length,
a fact well shown in the folds of the esophageal canal when the stylet
is retracted. The males in this group are all of a vestigial character, in
some species very rare or even unknown, and their stylets are usually
weak and degenerate (Fig. 26).

MIGRATORY NEMATODES
In contrast to the various types of fully or partly sedentary root-
parasitic forms, there exists a large group of migratory nematodes be-


37





DEPARTMENT OF AGRICULTURE


longing to several different genera and families. These may be classed
into those forms that enter the tissues, move through the root and live
inside it, as well as others that puncture a root and feed on it from the
outside.
The most important of the first mentioned group, i.e. those of endo-
parasitic habit, are those species belonging to Pratylenchus Filipjev and
related genera, or the so-called meadow nematodes. We know of at least
four different species of Pratylenchus from Florida alone. Meadow
nematodes are also widely distributed elsewhere. They attack the roots,
tubers, rhizomes, corms, or bulbs of various crops. Occasionally they
are also found in stems. A short, stout body and a strong buccal stylet
make them migratory, tissue parasites, par excellence. From an economic
point of view they are major pests. Unfortunately, their significance,
common occurrence, and widespread distribution have been almost com-
pletely ignored until very recently. The various species are difficult to
distinguish and their classification is still greatly confused. A form at-
tacking the Irish potato was recorded as one of the first plant nematode!
pests in this country. It is Pratylenchus scribneri Steiner which was
observed in 1889 by F. Lamson Scribner on potatoes in Tennessee. It
was not given a name then, but recently has been established as a true
species. Observed in different states east of the Rocky Mountains, it
appears to occur exclusively on potatoes. A second species, P. leiocepha-
lus N.Sp., well characterized by the angular contour of its head, has
been found on potatoes in Florida as well as on a variety of other crops.
(Fig. 27). While these two species are monosexual forms, there are
other species which are bisexual. In entering and migrating through
root tissues they destroy them by breaking through cell walls and feeding
on their contents with organisms of decay following in their wake. Root
tissues penetrated by meadow nematodes usually exhibit necrotic lesions



Figure 26.-Paratylenchus elachistus n.sp.,1 a pin nematode that was found
attacking the roots of ramie (Boehmeria nivea (L.) Gaud.) in the region of Clewis-
ton, Fla. Material collected by W. D. Wylie, December 1943. A. Female; cer
ppl, cervical papilla; lat fld, lateral field, X 500. B. Head end of female; dsl
oe gl, dorsal oesophageal gland, ampulla outlet; subv oe gl, subventral oesophageal
gland outlet; X 1800. C. Male; phas, phasmid (?); X 500.

'Diagnosis: Paratylenchus resembling P. besoekianus Bally & Reydon 1931
and P. bukowinensis Micoletzky 1922 but different from the first (a) by its weaker
but slightly longer buccal stylet (21-22A in P. elaschistus, 18.8u1 in P. besoekianus);
(b) by complete absence of a postvulvar uterus branch; (c) by its much longer
ovaries which in most specimens reach forward to the nerve ring, not infrequently
even close to the base of the buccal stylet; (d) by its longer spicula (16u instead
of 12,u) and (e) by its shorter gubernaculum. It is different from P. bukowinensis
(a) by the smaller size of the 9 (0.234-0.304 mm as against 0.390 mm); (b)
by complete absence of a postvulvar uterus and (c) by the stronger buccal stylet
and its larger, more distinct basal knobs.
Measurements: total length = 0.267 mm (0.234-0.304 nmm); a = 19.8 (16.9-
23.5); 3 = 3.9 (3.6-4.2); 7 = 13.1(10.5-15.0); vulva = 83.4% (82-86.6%). .
total length = 0.257 mm (0.222-0.248 mm); a = 26.1(23.6-30.5) ; 1 3.89 (3.35-4.5);
7 = 11.7(10.9-13).
Type location: Clewiston, Fla.; Type host: ramie (Boehmeria nivea (L.) Gaud.)


38





PLANT NEMATODES THE GROWER SHOULD KNOW 39
Figure 26


ph/s. -C


C






DEPARTMENT OF AGRICULTURE


which frequently are reddish in color at first, turning dark brown to
black later on. The eggs are deposited within the roots, where, not
uncommonly, accumulations of specimens, including larval stages, adults
and eggs, may be seen occurring as "nests". Observations show these
forms to be extremely destructive (Fig. 28 A & B) since by attacking
and destroying a root at a point close to the stem they render useless the
entire distal portion of the organ. Certain plants try to repair the
damage by forming new side roots above the attacked points. Then as
new lesions are developed on these side roots still more side roots are
formed with the result that root systems attacked by these nematodes
frequently exhibit a bearded or matted appearance. Sometimes the
cortex of roots so attacked begins to decay and then easily slips off.
The axial cylinder is rarely entered. On potatoes surface pimples are
formed which later change to blackish depressions. When very numerous,
these pimples and depressions disfigure the tubers to such a degree that
the crop is rendered unmarketable (Fig. 29). Under certain conditions,
particularly in orchards and on perennials where they remain undisturbed
for years, they may multiply to enormous numbers. Cases have been
observed where large trees lose significant portions of their root systems
by the attacks of great numbers of these meadow nematodes, with the
result that branches, limbs, parts of the crown, and even entire trees
show the effect by yellowing foliage, defoliation, death of limbs and
branches or even of whole trees. It is difficult to estimate the damage
caused by this type of nematode on plants. They cannot live on dead,


Figure 27.-The smooth headed meadow nematode, Pratylenchus leiocephalus
n.sp.' A. Adult female; X 333. B. Anterior end; note the 3 nuclei of the
oesophageal glands and their arrangement; nrv r, nerve ring; X 500. C. Head
end; note the angular outline of the head proper and the 3 basal knobs of the
buccal stylet which are so well amalgamated as to appear as a single spherical
knob; X 1222. D. Front view of head; amph, amphid, a chemical sense organ;
cph ppl, cephalic papilla, an organ of touch; X 1222. E. The basal knobs of
the buccal stylet as seen in optical cross section; X 1222. F. Tail end of female,
drawing to show the annulation of the cuticle and its interruption by the lateral
field; phas, phasmid, an outlet of a gland; X 500. G. Tail end; anus; phas,
phasmid; vlv, vulva; note the short postvulvar uterus branch; X 500. H. Tail
end in ventral view; anus; phas, phasmid; vlv, vulva; X 500. 1. Egg as it is
deposited; note the kidney form which is characteristic for Pratylenchus eggs;
X 500. J. Egg containing larva of which the pear-shaped end bulb of oesophagus
is to be seen; X 500. K. Egg with larva of which tail end is to be seen; X 500.

1Diagnosis: Monosexual Pratylenchus; head of angular contour and composed
of only two annules; buccal stylet strong (18,u long), with large basal knobs, all
three together forming a compact, almost single-appearing globular swelling; lateral
fields narrowing behind vulva, middle striae (longitudinal grooves) uniting in front
of anus and then fading in front of or at phasmid; oesophageal glands forming
short, compact body, about half of which overlaps intestine. Intestine with uniform
globulation; tail broadly obtuse, tip not annulated. Vulva at about 87%, or 1/2
to 2 times length of tail in front of anus; ovary never reaching oesophagus, con-
sisting of single series of about 17 oicytes; postvulvar uterus sac very short. Eggs
about 20 X 72u.
Measurements: Y total length = 0.395-0.632 mm; a = 15-20; P = 5-6;
" = 17-20; vulva = 86-89%.
Type host: peanuts (Arachis hypogaea L.); Type locality: Fairhope, Ala.


40






PLANT NEMATODES THE GROWER SHOULD KNOW 41


Figure 27























!~phai' D
B pp(
.CIp4 as


G fr





DEPARTMENT OF AGRICULTURE


decaying tissues and are not generally found in roots in the process of
decay. Such roots abound with a variety of fungi and bacteria and
so-called saprophytic nematodes, while the primary culprit has escaped
to the surrounding soil or to still healthy tissue. The study of the
meadow nematode is still in its infancy. Experimental work with this
group is difficult because of their small size and their migratory way
of life.
There exist, of course, many other nematode parasites of similar
habits that belong to the same or related taxonomic groups, but the


b%
:I^



A *


A


B


Figure 28.-A and B. Root systems of two dying corn seedlings (Zea mays L.)
heavily attacked by the smooth headed meadow nematode (Pratylenchus leiocephalus
n.sp.) (see Fig. 27). These seedlings were collected by R. J. Humphrey near
Sanford, Fla.


42


rl








PLANT NEMATODES THE GROWER SHOULD KNOW


eadow nematodes are apparently the most destructive and most widely
distributed.
MISCELLANEOUS TYPES

Since it would not be possible to mention here all these other types,
nly a few will be listed. Some are known to occur in Florida and
their southern states. Among them the hoplolaims or lance nematodes
specially should be mentioned. They appear to be mainly a tropical
nd subtropical group of migratory root parasites. Various species from
lorida soils are known to us, while farther north only one form, Hoplo-
aimus coronatus Cobb, as yet has been observed. The lance nematodes are
tout, cylindrical, rather large-sized parasites with an extremely strong
uccal stylet, the tail end usually being obtuse and the cuticle coarsely
annulated. They somewhat resemble the meadow nematodes in their
life habits and may also occur in large numbers on roots if undisturbed
for considerable periods of time. In combination with other pathogenic
agents and adverse environmental conditions such as drought, a killing
effect by these nematodes has been observed, particularly on seedling
plants. In Florida they have been noticed as pests in forest nurseries,
parasitizing seedlings of the slash pine, Pinus caribaea Morelet, and the
longleaf pine, Pinus palustris Mill. Often only surface parasites, the
hoplolaims may also enter the roots with the whole body. They are
therefore endo- as well as ectoparasites (Fig. 30).


















Figure 29.-Potatoes attacked by Scribner's meadow nematode (Pratylenchus
scribneri Steiner). The figure at left shows a potato with a lighter infection, while
that of the one at right is very heavy. The arrow in the figure at right points to a
single small lesion from which alone 335 nematodes were isolated; thus the
nematodes in this potato were conservatively estimated at from 12,000 to 15,000.

Other extremely interesting types are the awl nematodes, Dolichodorus
heterocephalus Cobb (Fig. 31), and the sting nematode, Belonolaimus
gracilis n.g. n.sp. (Fig. 32). Both are found in Florida and both feed


43






DEPARTMENT OF AGRICULTURE


4-


Figure 30.-Drawing of a root fragment of longleaf pine (Pinus palustris
Mill.) exhibiting the posterior ends of three different specimens (arrows) of
Hoplolaimus coronatus Cobb protruding from the broken root surface; 65 specimens
were counted from a piece of root one inch long. Material collected by the author
near Tifton, Ga., November 1940; X 136.

on roots which they puncture from the surface with their long needle-
or awl-shaped buccal stylets. The former was observed on celery roots
near Sanford. The latter was found on corn roots, also from Sanford,
and on roots of slash and long leaf pine seedlings in various forest
nurseries (Ocala, Brooksville, Valparaiso).
Many additional types of root-attacking nematodes could be men-
tioned. Usually most of them occur only in smaller numbers and are
not known to cause serious diseases. Future research, however, may
uncover many surprises.


44




















































D


Figure 31.-The awl nematode, Dolichodorus heterocephalus, Cobb, an interest-
ing type of root parasitic nematode because of its awl-shaped, long, buccal stylet
and the trilobed bursa in the male. A. Anterior end; dsl oe gl, outlet of dorsal
oesophageal gland; X 500. B. Cross section through middle region of body to
show the structure of the lateral fields consisting of two longitudinal bands
separated by three longitudinal grooves; gr lat, grooves in lateral field; X 500.
C. Tail end of 9 seen dorsally; anus; phas, phasmid; X 500. D. Tail end of
S seen dorsally to show the trilobed bursa; phas, phasmid; sp, spicula, gub,
gubernaculum; X 500. The specimens of this parasite here partly sketched were
collected by A. L. Taylor on celery roots near Sanford, Fla. in December 1943.
In the "Plant Disease Reporter" of December 15, 1943, p. 707 they were recorded
as a species of a genus closely related to Paratylenchus; however, it is now
certain that Dolichodorus represents a separate subfamily not directly related to
Paratylenchus.






46 DEPARTMENT OF AGRICULTURE

Figure 32






PLANT NEMATODES THE GROWER SHOULD KNOW 47

Figure 32.-Belonolaimus gracils n.g., n.sp.1, the sting nematode, an undescribed
species representing a new genus. It has been observed attacking the roots of
slash pine and longleaf pine seedlings in various forest nurseries in Florida. A.
Head end; o gl, outlet of dorsal oesophageal gland; X 450. B. Tail end of $
in ventral view; phas, phasmid; X 450. C. Tail end of 9 in side view; phas,
phasmid; X 450.
1Diagnosis of new genus Belonolaimus: Tylenchidae closely related to Dolicho-
dorus Cobb 1914 but different through the absence of a distinct terminal bulb in the
oesophagus and through presence of enlarged oesophageal glands which overlap the
anterior intestine; female tail cylindrical, broadly obtuse, annulation following con-
tour of terminus; male bursa not lobed, enveloping tail end. Type species: Belono-
annulated; annules laterally interrupted by single groove. Head distinctly se'2
off, four lobed, annulated. Buccal stylet about 157, long with rounded basal
knobs. Procorpus short, containing large ampulla of dorsal oesophageal gland, its
outlet near base of stylet; oesophageal canal much folded as stylet is retracted.
Middle bulb spherical, with large valves. Isthmus short; end portion of oesophagus
consisting of three much enlarged gland cells overlapping the anterior end of the
intestine; the latter granular, rather opaque, its cavity obscure; rectum and anus
also rather inconspicuous. Female sexual apparatus amphidelphic. Spicula in
side view slightly arched, of about same width their entire length, distally pointed;
gubernaculum about 2/5 length of spicula; bursa with one short rib representing
the phasmid, on each wing near middle of tail.
Measurements: 9 total length = 2.15mm; a = 52; 3 = ?; 7 = 19.2;
vulva = about 52%
6 total length = 1.7mm; a = 52; -= ?; = 14.7
Type location: Ocala, Fla. Type host: Slash pine, Pinus caribaea Morelet.


eert: laimus gracilis n.sp. Diagnosis of new species B. gracilis: Body cylindrical, cotrILAI




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