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Group Title: Bulletin State of Florida, Dept. of Agriculture
Title: Plant nematodes the grower should know
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Title: Plant nematodes the grower should know
Alternate Title: Bulletin - State of Florida, Dept. of Agriculture ; 131
Physical Description: 48 p. : ill. ; 23 cm.
Language: English
Creator: Steiner, G. ( Gotthold ), b. 1886
Soil Science Society of Florida -- Meeting
Florida -- Dept. of Agriculture
Publisher: State of Florida, Dept. of Agriculture
Place of Publication: Tallahassee, Fla.
Publication Date: January, 1953
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Subject: Plant nematodes -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
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Statement of Responsibility: G. Steiner.
Bibliography: Includes bibliographical references.
General Note: Reprinted from the Fourth proceedings of the Soil Science Society of Florida, 1942 (Publ. Apr. 1, 1949).
General Note: "January, 1953".
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Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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oclc - 32777977
alephbibnum - 002567631

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Full Text
NOV 30 153


Bulletin No. 131 New Series January, 1953





| PLANT NEMATODES

THE GROWER SHOULD KNOW A

















STATE OF FLORIDA
DEPARTMENT OF AGRICULTURE
| NATHAN MAYO, Commissioner
TALLAHASSEE

Reprinted from the Fourth Proceedings of the
SSoil Science Socfety of Florida
)4.
v{a)))*-a)*)>3))) 3>4a4.







PLANT NEMATODES THE GROWER SHOULD KNOW
G. STEINER'
PART I2
In yesterday evening's address" an attempt was made tq
present to you a general picture of the significance of nematode,
as part of the biological component of the soil. During today's
presentation, in accordance with your request, I shall try to givE
a review of nematode forms and types that are considered ol
importance to the grower because of a direct or indirect relation
ship 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
phathogens and therefore of significance to plant growth and
crop production. But only during recent years has an increasing
realization of the economic significance of plant nematodes as
pests of crops, and as limiting factors in crop production been
developed by growers and research workers. That 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 para-
sitized 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 modifying 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 root-knot nematodes
recognized the world over as the worst and most perplexing agri-
cultural pests they are certainly not the only significant ones.
There are many other important plant nematodes such as the
meadow nematodes (a group of forms belonging to the genus
Pratylenchus Filipjev); the spiral nematodes (Genus Helicoty-
lenchus Steiner)4; the kidney-shaped nematode (Genus Roty-
lenchulus Linford); the lance nematodes (Genus Hoploaimus v.
Daday) ; the puncturing nematodes (Genus Dolichodorus Cobb);
the stylet nematodes (Genus Tylenchorhynchus Cobb) ; the ring
nematodes (Subfamily Criconematinae Chitwood) ; the pin nema-
todes (Genus Paratylenchus Micoletzky) ; the seed gall nema-
todes (Genus Anguina Scopoli), to which belongs, e.g., the wheat
nematode (A. tritici [Steinbuch] Filipjev); the bulb and stem
1 Principal 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.
3 Nematodes and the life association of the soil, p. 7, this volume.
4 Steiner, G., 1945: Helicotylenchus, a new genus of plant-parasitic nema-
todes and its relationship to Rotylenchus Filipjev. Proc. Helminthological
Soc. Washington. Vol. 12, 34-38, fig. 1A-F.





C PLANT NEMATODES THE GROWER SHOULD KNOW 3

nematodes (Genus Ditylenchus Filipjev), which represent a group
of different species including, e.g., the rice nematode (Ditylenchus
angustus [Butler] Filipjev) and the potato rot nematode (Dity-
lenchus destructor Thorne) ; the sugar-beet nematode (Heterodera
schachtii Schmidt) ; the golden nematode of potatoes (H. rosto-
chiensis Wollenweber) ; the citrus nematode (Genus Tylenchulus
Cobb) ; the bud and leaf nematodes (certain species of Aphelen-
choides Fischer) such as the fern nematode (A. olesistus Ritzema
Bos), the cocopalm nematode (A. cocophilus Cobb), the straw-
berry 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
I 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 cer-
tainly underestimated. There are several reasons for this. One
is the soil-borne character of all plant nematodes; a second, 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
I is technically very difficult; a fifth, that they are considered a
border subject not properly belonging to the field of the entomol-
ogist or that of the plant pathologist or the parasitologist. In
addition plant nematology and its related subject-soil, fresh-
water, and marine nematology-are not given as courses in our
colleges and universities and are considered only a side line of
research by most agricultural institutions.
Then, too, there is the tendency on the part of growers and
investigators 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 up-
rooting 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





DEPARTMENT OF AGRICULTURE


applications of fertilizers. We are convinced that many 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 continue to produce, notwithstanding fertilizer appli-
cations 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.
Is 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 there-
fore increase tremendously, particularly in the absence of any
natural checks. But here again in our attempts to look for andl
control pests and diseases, the above-ground parts of our crops
have attracted most of our attention and consumed most of ourl
efforts. This has led to modern pest control of these aerial parts
by spraying and dusting practices and by fumigation. 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 relationship 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, har-
rowing, and cultivation are some of the operations that help and
are not to be under-estimated as a means of reducing noxious
nematodes in the soil. This is accomplished by exposing the nema-
todes 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 population
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.





S PLANT NEMATODES THE GROWER SHOULD KNOW 5

I This situation began to change with the coming of soil sterili-
zation by steam and other means including the use of efficacious
Poil fumigants. 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 production. But
ere 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
iof 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
'ade 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), chloropicrin (C C13NO2), methyl
bromide (CH3Br) and others, including the most recent DD
mixture (1.3 Dichloro-propylene-[CHCl=CH-CH2C1] Dichloro-
propane- [CHCl-CHCl-CH:], 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.
ISuch 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,
nematode control. The results of soil fumigation in our opinion
thus emphasize 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
pof 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 lesser need
for fertilizers. Let us provide healthy root systems for our crop
Plants through control of the many nematodes and other agents





DEPARTMENT OF AGRICULTURE


now causing root lesions, root decay, root amputations, blind rootl
tips, abnormal matted growth, etc., and surprising yield increases
will result. A healthy root system will more effectively utilize
lower fertility level in a soil or take more advantage of one that
has been artificially increased by fertilizer applications, than wilI
one that is affected by disease.


Figure 1.-Roots of a tobacco plant grown in South Carolina and dis-
figured through a heavy infection by root-knot nematodes. 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 micro.
scopic nematode pests on their crops, and how are they to know
the kinds involved? Are there specific symptoms which indicatet
that a disease or abnormal behavior is caused by a nematode, or
an association of nematodes, or a combination of nematodes and(
fungi or bacteria, or a combination of all three of them, or a
combination of still some other factor or group of factors with,

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 I
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. I




I PLANT NEMATODES THE GROWER SHOULD KNOW 7

lhematodes? Unfortunately there exists only one sure way to
determine this, namely the location and identification of the
'ematodes themselves. May we therefore emphasize that it is
not possible to recognize and properly diagnose nematode diseases
f plants 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 nematodes may be correctly
recognized and properly diagnosed through the symptoms they
cause on the roots of host plants, namely conspicuous swellings,
nots 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 root-knot nematodes because: (1) there
are knot-forming nematodes found on roots of plants other than
khe root-knot nematodes (e. g. Ditylenchus radicicola [Greeff]
Filipjev, or Nacobbus dorsalis Thorne & Allen), (2) root-knot
nematodess may be present without causing the formation of knots
1(this is often seen, e.g., in cotton or corn where the nematode
breaks through the surface of a root without forming knots) and
oots are then mistakenly judged free, (3) other organisms may





















I owl
4I












Figure 2.-Roots and pods of a peanut plant (Arachis hypogaea L.)
infected with root-knot nematodes 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.







-, -


4


Figure 3.-Seedlings of one of the rubber-producing dandelions (Taraxacum koksaghyz Rod.) ex-
hibiting root swellings caused by the root knot nematode.




PLANT NEMATODES THE GROWER SHOULD KNOW


SA hB
Figure 4.-A. Heavily knotted and crippled roots of a Laredo soybean
plant grown in Virginia infected with root-knot nematodes; 2/3 normal
size. B. Heavily knotted and crippled roots of a young Castilla elastica
Cerv.; 2/3 normal size.




DEPARTMENT OF AGRICULTURE


/


C


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


11





PLANT NEMATODES THE GROWER SHOULD KNOW 11

Form similar knots, e.g. the slime molds (Plasmodiophora species)
causing clubroots in members of the cabbage family, the crown
g gall organism (Bacterium tumefaciens Sm. & Town) and certain
viruses; also so-called bacterial nodules may be mistaken for
Sroot-knot galls, but they usually are easily distinguished from
knots caused by root-knot nematodes by the fact that they
are mostly fixed on a short peduncle and hang on the side of a
I root whereas the swelling caused by root-knot nematodes 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


B
- ~. y


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 root-knot
nematodes. C. Carrot disfigured and made unmarketable by root-knot
nematodes; % normal size.




12 DEPARTMENT OF AGRICULTURE


D W E Ei
Figure 7.-A. Bliss triumph potato badly infected and disfigured by
root-knot nematodes. Specimens collected at Gainesville, Florida. Note the
protruding knobs formed by the nematode and compare with B where symp-
toms are sunken, crater-like spots. B-E. Bliss triumph potato infected and
disfigured by root-knot nematodes. 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 populations; 2/3 normal size.


2,
:
;8
'h-





S PLANT NEMATODES THE GROWER SHOULD KNOW 13

Common root-knot nematode disease must be diagnosed by the
presence of the organism itself rather than through the occurrence
I of knots of one kind or another on the roots.
Furthermore, for a proper assay of the status of a given
i plant as a host, it should be ascertained whether the nematode
is actually producing progeny on it. For a demonstration of this
point root-knot nematodes may serve again. Our observations

























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 root-knot nematodes; 1/ 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.
appear to show that these pre-parasitic larvae enter the roots
or subterraneous stem and leaf formations of almost any type
of plant in spite of the fact that, in most cases, they are un-
able 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 nematodes that invaded these roots were





DEPARTMENT OF AGRICULTURE


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 nematode 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.),


4!




0t
--,
r a^


Figure 9.-Lespedeza stipulacea Maxim., Korean clover, showing nodules
caused by root-knot nematodes (solid arrows), and nodules caused by
beneficial nitrogen-fixing bacteria (open arrows). Coll: Virginia, 1941; 2/3
normal size. It may be mentioned that this lespedeza is an excellent indicator
plant to detect the presence of root-knot nematodes in the soil. Where
these nematodes occur in a soil growing this species, the plants always will
be stunted and yellow.




I PLANT NEMATODES THE GROWER SHOULD KNOW 15

b'dusty miller" or silver cineraria (Senecio cineraria DC.),
Nicotiana megalosiphon Huerck & Muell. Arg. and Nicotiana
fplumbaginifolia Viv. Crotalaria spectabilis proved to be one of
the most interesting plants yet studied in its host-parasite relation-
ship with root-knot nematodes. 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
as been found very effective in cleaning infested land of root-
not nematodes. In entering the roots the nematode appears
to be able to induce the root tissues to produce the so-called giant
lor nectarial cells on which they feed, but for some reason the
nematodes 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
Pthe 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
IBrazil5 and used there as a root stock for tomato grafts on root-
knot-infested lands, exhibits characteristics quite similar to those
lof Crotalaria spectabilis in its relationship to the root-knot nema-
Ptodes. Here, too, the roots are invaded and their tips blinded by
the larval root-knot nematodes which again are unable to grow
land develop as they become fixed. The 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
lnd 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 occasional 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 root-knot nematodes 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 root-knot nematodes, including the so-called resist-
ant and immune types, will bring to light additional information
lof much value for a better understanding of these numerous
and complex host-parasite inter-relationship. These are all
I matters of not only theoretical interest, but of great practical
5 For the opportunity of studying this plant we are indebted to S. B. Fenne
I of the Institute of Inter-American Affairs.




DEPARTMENT OF AGRICULTURE


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 difficult. Observations on the host range of*


-1


~~f'


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




* PLANT NEMATODES THE GROWER SHOULD KNOW 17

this nematode in different regions and locations, as well as studies
on the resistance of an identical crop 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 many different species or host nematodes, each of which
has its own host range; some regions or localities appear to have
'only a single species, whereas in others two or more occur,
often in a mixed state. A similar situation appears to exist in
bother nematode species, for example, the bulb and stem nematode
or certain bud and leaf nematodes (Aphelenchidae species). These
matters are mentioned to emphasize 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
Sthe entire plant, blinding of buds, .nd 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
[exhibiting 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.
S Nematodes, or eelworms, so far as plant-parasitic forms are
concerned, are very small animals, less than 2 mm long, usually
I 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. Although of such small size, their organi-
zation is highly complex and embraces all organs and organ-
systems found in higher animals except a circulatory system. It
Sis difficult for the untrained worker to differentiate the various
genera and species and some of the thousands of soil-inhabiting
i forms may easily be mistaken for those which are definitely
parasitic to plants. The grower and entomologist as well as the
I 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 signifi-
I chance of these forms are subject to a great deal of change and
modification.
It has already been pointed out that nematodes constitute an
extremely 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.




A B C .
...stomato-styglet. odonto-stylet...


/ \ -outl ad oes gI \ nr c


.l d .. ...out ds oes gl ...


out rt suh out rt su J
W -- .. Oes g -- /


--. / r.--- dsl oesgL .


.I ubv oes gl i ..t sub oes gi..


ddoesgl.-




Tylenclhidue Aphelenchidwe Dorylaii aoe

stomato-stylet odonto-stylet

stylet a transformed stylet
buccal cailty transformed tdMth
Figure 11.-Schematic drawings to explain the main differentiating char-
acters of the three groups of nematodes to which most plant-parasitic $orms
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 subventral oesophageal gland; rt subv oes, gl, |right
subventral oesophageal gland.





I PLANT NEMATODES THE GROWER SHOULD KNOW 19

I This organ appears to be fully effective in puncturing the plant
tissues, and in obtaining the food required by these parasites by
I sucking. Furthermore, many types of plant-parasitic nematodes
appear to induce the host plant to produce their particular food
I requirements by injecting into the plant tissues the secretions of
their large esophageal or salivary glands. For this purpose the
stylet is used as an injecting needle.
S The stylet of the tylenchs and also that of the aphelenchs is
called a buccal stylet or "stomato-stylet." It is assumed to have
I 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 represent a group of very






























F A B C D E
Figuie 12.-Drawings of various developmental stages of a 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




___ _Y___VV


.D




























Figure 13.-Photomicrographs of developing larvae of a root-knot nema-
tode in roots of balsam (Intpatiens balsacnina 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 oesopha-
geal glands into the root tissue. These injections stimulate the cells to in-
creased 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 or 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).


j


'I





PLANT NEMATODES THE GROWER SHOULD KNOW 21

I different origin and relationship, the stylet is assumed to be a
transformed tooth and is therefore termed an "odonto-stylet."
I (Fig. 13).
The tylenchs and aphelenchs include the most outstanding plant
Snematode 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 alimentary 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.
The dorylaims occur in numerous genera and species in soils
everywhere. 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 pronounced 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 parasite. 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 trans-
formation 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 importance than others. It is with these species
that we will first deal.
THE ROOT-KNOT NEMATODE
Root-knot nematodes (Meloidogyne spp., formerly Heterodera
marioni [Cornu] Goodey) are considered the most important of
this group. Their extended distribution through the tropics, sub-
tropics, and temperate regions and their occurrence in green-
houses everywhere, make them one of the most widely distributed
and common agricultural pests. They have 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





DEPARTMENT OF AGRICULTURE


nematode, was not discovered until 1879, and was first definitely I
established as occurring in Florida in 1889. While root-knot
doubtless is now present in all sections of the State it is particu-
larly bad in those areas where sandy and peaty soils prevail,
where it causes damage in various ways that may well be esti-
mated at several million dollars annually. It also has been re-
ported to occur in almost every State of the Continental U. S. A.
Although these organisms were formerly thought incapable of I
surviving the winter in the northern part of our country, this is
a misconception, for experiments and observations show some
species fully capable of withstanding extreme cold when in the
soil, and of surviving temperatures as low as 10"F. if exposed.
Root-knot does not cause such extensive damage farther north,
however, as it produces under warmer climatic conditions, appar-
ently because northern summers are short and cool, thus prevent- I
ing the development of more than one or two generations.
In the description of the life cycle of the root-knot nematodes I
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. 13A) and, with its short buccal stylet, insects
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 pro-
duces 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
produced 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 conditions, 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 suc-
cumbs quickly to adverse conditions such as lack of moisture,
excessive heat, direct sunlight, or cold. Males develop under
certain conditions but they appear to play no role in the production





I PLANT NEMATODES THE GROWER SHOULD KNOW 23

Sof 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


A


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


~--~iC"=:
:.-
'.





DEPARTMENT OF AGRICULTURE


females, a male larva at the sausage-shaped stage is transformed I
into a threadlike, cylindrical nematode folded and wound up inside
the larval molt from which it finally escapes as a mature male. |



I












r.
























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




I PLANT NEMATODES THE GROWER SHOULD KNOW 25

S It is evident that during its life cycle a 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 important point. Fumigants applied to the
soil sometimes reach only larvae and eggs free in the soil, while
specimens inside a root, particularly if it is woody, may not be
I affected. The complete uprooting of plants will eliminate all stages
inside the roots-eggs, larvae, and adults-if the roots are de-
stroyed. The development of the larvae is interrupted if the root
on which they are feeding is disturbed, and they will perish when


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




26 DEPARTMENT OF AGRICULTURE

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 migra-
tion is slow.
Over 1700 different plant species are known to be attacked


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.
X3





I PLANT NEMATODES THE GROWER SHOULD KNOW 27

I by root-knot nematodes. However, they exhibit a wide varia-
tion in the 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 germi-


Figure 18.-A. Photomicrograph of a larval specimen of a root-knot
nematode in the tissue of the same potato shown in Figure 17. B. Photo-
micrograph of an egg mass of the nematode in the tissue of the same potato
as shown in Figure 17. x85




DEPARTMENT OF AGRICULTURE


nating seeds and young seedlings are particularly attractive to I
root-knot nematode larvae (Fig. 8) including even seedlings of
plants otherwise immune or highly resistant. Seeds should there- I
fore never be planted in soil badly infested by root-knot nema-
todes, 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 susceptible 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
nematodes break through the root surface so that the egg-pro-
ducing females protrude from the root and may then be seen with
a hand lens as globular, whitish bodies with yellowish or brownish
egg masses attached. Sometimes 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 nematodes 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 these
nematodes with the conception that galls or knots are its symp-
toms, have often considered the nematode absent because there
were no galls. Thus they have missed the root decay initiated
by the nematodes which is usually much more serious than the
galls.

SEDENTARY TYPES
This leads us to other sedentary types of plant-parasitic nema-
todes 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 con-
trast with root-knot nematodes, 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 trans-
formed are then called "cysts" and may remain in the soil for
years, releasing active larvae over a period of years. This phe-
nomenon not only complicates 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 chemi-
cals. We know of no species of this group occurring in Florida
but are convinced that at least one form, Heterodera weissi,





I PLANT NEMATODES THE GROWER SHOULD KNOW 29

I n. sp." (Fig. 19) may be present. It is found on various species of
knotweeds and is known to us to occur in numerous states east
Sof the Rocky Mountains, as far south as the Delta section of
southern Missouri and the region of Ridgeville, Georgia.
Root-knot nematodes, together with the various species of the
sugar-beet nematode group, represent sedentary root parasites
which are all closely related and difficult to differentiate. The


Figure 19.-A. Male of Heterodera weissi n. sp., the knotweed heterodera,
I 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.

Diagnosis: Heterodera with small, lemon-shaped cysts (330 to 404A x 590
I to 617u) 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
I annulated, well set off, semi-spherical head; buccal stylet of about 28-29,;
ventral terminal anus with protruding lips; spicula 34A; gubernaculum 10f;
a = 35-36; 3 = 8.4-11.8; -y = about O. Eggs 32 to 42, x 81 to 1141. Prepara-
sitic 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.





DEPARTMENT OF AGRICULTURE


7-~;


-.root


.. type of Wa


. lv


Figure 20.-Drawing of a female of the citrus nematode, Tylenchulus
semipenetrans 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; viv, vulva.




I'-E II INl]ilVIAr 1U1j Ir[ IlT I NUIJVVT


,.l.. I --' -..;
--U



A.r








Figure 21.-The kidney-shaped nematode, Rotylenchulus reniformis Lin-
ford. A. Pieces of roots of Jacquemontia tamnifolia L. Griseb with speci-
mens 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 greenhouse. X 170.


-_ __ I





DEPARTMENT OF AGRICULTURE


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
resulted in transformation of the female by globular inflation.
The same phenomenon is seen in other genera of quite different
origin and relationship; an outstanding example is Nacobbus,
a form only recently described by Thorne and Allen from Cali-
fornia. 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
another 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 sur-
face 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 increases in size
while developing from the larval to the adult stage.
There is still a fourth type of swollen sedentary root parasitic
nematode, the kidney-shaped nematode (Rotylenchulus reniformis
Lindford). The parasitic female is attached to the root surface
but its body is surrounded by a spherical structure which it forms
for itself by secreting a glabrous substance which also surrounds
the eggs and cements together adjacent soil particles. We located
this interesting species recently from Florida on roots of tomato

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 civellac n.sp.,2 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.

I 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 50A long; middle bulb of
oesophagus only about 12 width of body cavity; isthmus and terminal bulb
much longer than in C. sphaerocephalum.
Measurements: Total length of 9 = 0.252mm; a = 8.4; p = 2.3; = 31.5
Type host: Citrus aurantium L.; Type locality: Orlando, Florida.
2 Named for Mrs. Civella Adams Chambliss, Scientific Aid in the Division
of Nematology, 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 pos-
terior edge. Annules numbering from 58 to 62. Buccal stylet 68M. Total
length = 0.376 mm. Type host: Citrus grandis.





I PLANT NEMATODES THE GROWER SHOULD KNOW 33


- ol/dsJoesp!/












..0I

*rlr


Figure 22




DEPARTMENT OF AGRICULTURE


and coffee weed (Cassia tora L.) sent to us from Quincy. As in I
the citrus nematode, the anterior portion of the body of the female
is elongated and is inserted into the root while the reniform, main I
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, Roty-
lenchulus is very difficult to see and may easily be overlooked or
mistaken for globular soil agglutinations adhering to the root I
(Fig. 21).
It is obvious that all these sedentary nematodes with inflated I
and obese bodies that become fixed in or on a root lose their


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.




PLANT NEMATODES THE GROWER SHOULD KNOW 35
Imotility and are unable to change their position and migrate. If
roots containing such stationary parasites are uprooted and de-
Istroyed before the parasites are fully grown or before they have
produced eggs, the source of infection 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
I various types by their own means is very restricted. Thus long
distance travel is entirely one of transportation by such carriers
Ias wind, water, and particularly man, who spreads them with
plant material of all kinds and with soil.
I There exist other sedentary root parasitic nematodes which
in contrast with the foregoing groups have preserved a certain,
though reduced, motility; they are called ring and scale nema-
Stodes and include various genera and numerous species belonging


N


*,1




I


S.


/'


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.




DEPARTMENT OF AGRICULTURE


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 tissues; 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 37

'to the Criconematinae and other related groups (Fig. 22 A & B).
They too are ecto-parasites, puncturing the surface of roots
I(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. Procri-
conema Micoletzky) are of pronounced, sedentary habit (Fig. 24).
They retain their moulting skins, which make an additional pro-
tection for their bodies while quite permanently attached to a
root. Locomotion of these animals with a double sheath around
Ithem would be extremely difficult.
Finally there are root-surface parasites with well developed
locomotive ability which nevertheless pass a sedentary existence
on roots for extended periods. One group of these are ancestors
of the kidney-shaped nematode previously mentioned. They are
forms widely distributed 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
I distribution. Where numerous they may seriously interfere with
plant growth. Helicotylenchus nannus Steiner is a small but very
I common species in the southeastern U. S. A., including Florida.
Of similar behavior are the pin nematodes (genus Paratylen-
Schus Micoletzky). The body of this genus, particularly that of
the female, is venturally 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 overlooked. It now appears that they
Iare rather common, sometimes occurring 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
I retracted. The males in this group are all of a vestigial character,
in some species very rare or even unknown, and their stylets are
I 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 belonging to several different genera and families.





DEPARTMENT OF AGRICULTURE


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. I
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, rhizones, corms, or
bulbs of various crops. Occasionally they are also found in stems. I
A short, stout body and a strong buccal stylet make them migra-
tory, tissue parasites, par excellence. From an economic point I
of view they are major pests. Unfortunately, their significance,
common occurrence, and widespread distribution have been almost
completely ignored until very recently. The various species are
difficult to distinguish and their classification is still greatly con-
fused. A form attacking the Irish potato was recorded as one
of the first plant nematode pests in this country. It is Pratylen-
chus 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. leiocephalus
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 I
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

Figure 26.-Paratylenchus elachistus n.sp.,t a pin nematode that was
found attacking the roots of ramie (Boehmeria nivea (L.) Gaud.) in the
region of Clewiston, 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; X1800. C. Male; phas, phasmid (?); |
X 500.
I
1 Diagnosis: Paratylenchus resembling P. besockianus Bally & Reydon
1931 and P. bukowinensis Micoletzky 1922 but different from the first (a) by
its weaker but slightly longer buccal stylet (21-22, in P. elaschistus, 18.81 in I
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; I
(d) by its longer spicula (16u instead of 124) and (e) by its shorter guber-
naculum. 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: 9 total length = 0.267 mm (0.234-0.304 mm) a= 19.8
(16.9-23.5) ; p = 3.9 (3.6-4.2) ; y = 13.1 (10.5-15.0) ; vulva =83.4% (82-86.6%).
8 total length 0.257 mm (0.222-0.248 mm); a = 26.1 (23.6-30.5); p 3.89 1
(3.35-4.5); 7 = 11.7 (10.9-13).
Type location: Clewiston, Fla.; Type host: ramie (Boehmeria nivea (L.)
Gaud.) I





PLANT NEMATODES THE GROWER SHOULD KNOW 39


Figure 26





40 DEPARTMENT OF AGRICULTURE

of decay following their wake. Root tissues penetrated by I
meadow nematodes usually exhibit necrotic lesions which fre-
quently are reddish in color at first, turning dark brown to black I
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 I
roots above the attacked points. Then as new lesions are de-
veloped on these side roots still more side roots are formed with
the result that root systems attacked by these nematodes fre-
quently 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. I
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

Figure 27.-The smooth headed meadow nematode, Pratylenchus leioce-
phalus n.sp.1 A. Adult females; 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 con-
taining 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.

1 Diagnosis: Monosexual Pratylenchus; head of angular contour and com-
posed of only two annules; buccal stylet strong (18k 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 87c, or 11/2 to 2 times length of tail in front of
anus; ovary never reaching oesophagus, consisting of single series of about
17 oocytes; postvulvar uterus sac very short. Eggs about 20 x 72p.
Measurements: 9 total length 0.395-0.632 mm; a = 15-20; [ = 5-6;
y = 17-20; vulva 86-89/%.
Type host: peanuts (Arachis hypogaea L.) ; Type locality: Fairhope, Ala.





PLANT NEMATODES THE GROWER SHOULD KNOW 41


a I j A


Figure 27


I~ ..i

ii : ri`\




DEPARTMENT OF AGRICULTURE


limbs and branches or even of whole trees. It is difficult to esti- I
mate the damage caused by this type of nematode on plants. They
cannot live on dead, 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 I
of their small size and their migratory way of life.
There exist, of course, many other nematode parasites of I


U;;


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




I PLANT NEMATODES THE GROWER SHOULD KNOW 43

Similar habits that belong to the same or related taxonomic groups,
but the meadow nematodes are apparently the most destructive
land most widely distributed.

MISCELLANEOUS TYPES
Since it would not be possible to mention here all these other
Types, only a few will be listed. Some are known to occur in
Florida and other southern states. Among them the hoplolaims
or lance nematodes especially should be mentioned. They appear
Ito be mainly a tropical and subtropical group of migratory root
parasites. Various species from Florida soils are known to us,
While farther north only one form, Hoplolaimus coronatus Cobb,
as yet has been observed. The lance nematodes are stout, cylin-
Sdrical, rather large-sized parasites with an extremely strong buccal
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
I with other pathogenic agents and adverse environmental condi-
tions 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
















Figure 29.-Potatoes attacked by Scribner's meadow nematode (Praty-
lenchus 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 nema-
todes were isolated; thus the nematodes in this potato were conservatively
estimated at from 12,000 to 15,000.

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).
Other extremely interesting types are the awl nematodes,
Dolichodorus heterocephalus Cobb (Fig. 31), and the sting nema-
tode, Belonolaimus gracilis n.g. n.sp. (Fig. 32). Both are found





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.
of the slash pine, Pinus caribaea Morelet, and the longleaf pine,
in Florida and both feed 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
mentioned. Usually most of them occur only in smaller numbers
and are not known to cause serious diseases. Future research,
however, may uncover many surprises.
HOST PLANTS
Many plants are more or less immune to root-knot, i. e., the
worms do not find their roots suitable medium in which to grow
and reproduce. Probably there are substances in the sap w ich
poison the worms. As a whole plants of the true grass family,





PLANT NEMATODES THE GROWER SHOULD KNOW 45


i i
MI S












j,








A' D
phar






Figure 31.-The awl nematode, Dolichodorus heterocephalus, Cobb, an
interesting 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 8 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 rep-
resents a separate subfamily not directly related to Paratylenchus.




46 DEPARTMENT OF AGRICULTURE


A C


Figure 32




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