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 Title Page
 Credits
 Table of Contents
 Introduction
 Review of literature
 Experimental studies
 Discussion
 Summary
 Literature cited














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 309
Title: Development of the root-knot nematode on beans as affected by soil temperature
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027329/00001
 Material Information
Title: Development of the root-knot nematode on beans as affected by soil temperature
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 15 p. : charts ; 23 cm.
Language: English
Creator: Townsend, G. R ( George Richard ), 1905-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1937
 Subjects
Subject: Root-knot   ( lcsh )
Beans -- Diseases and pests   ( lcsh )
Soil temperature   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 15.
Statement of Responsibility: by G.R. Townsend.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027329
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924389
oclc - 12197574
notis - AEN5009

Table of Contents
    Title Page
        Page 1
    Credits
        Page 2
    Table of Contents
        Page 3
    Introduction
        Page 3
    Review of literature
        Page 3
        Page 4
        Page 5
    Experimental studies
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Discussion
        Page 12
        Page 13
    Summary
        Page 14
    Literature cited
        Page 15
Full Text



Bulletin 309


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA
WILMON NEWELL, Director









Development of

THE ROOT-KNOT NEMATODE ON BEANS

As Affected by Soil Temperature


By G. R. TOWNSEND








TECHNICAL BULLETIN










Bulletins will be sent free to Florida residents upon application to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


April, 1937










EXECUTIVE STAFF
John J. Tigert, M.A., LL.D., President of
the University
Wilmon Newell, D.Sc., Director
H. Harold Hume, M.S., Asst. Dir., Research
Harold Mowry, M.S.A., Asst. Dir., Adm.
J. Francis Cooper, M.S.A., Editor
Jefferson Thomas, Assistant Editor
Clyde Beale, A.B.J., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant

MAIN STATION, GAINESVILLE

AGRONOMY
W. E. Stokes, M.S., Agronomist**
W. A. Leukel, Ph. D., Agronomist
G. E. Ritchey, M.S.A., Associate*
Fred H. Hull, Ph.D., Associate
W. A. Carver, Ph.D., Associate
John P. Camp, M.S., Assistant
ANIMAL HUSBANDRY
A. L. Shealy, D.V.M., Animal Husbandman**
R. B. Becker, Ph. D., Dairy Husbandman
L. M. Thurston, Ph.D., Dairy Technician
W. M. Neal, Ph.D., Asso. in An. Nutrition
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian
N. R. Mehrhof, M.Agr., Poultry Husbandman
W. W. Henley, B.S.A., Asst. An. Husb.*
W. G. Kirk, Ph.D., Asst. An. Husbandman
R. M. Crown, M.S.A., Asst. An. Husbandman
P. T. Dix Arnold, B.S.A., Assistant Dairy
Husbandman
L. L. Rusoff, M.S., Laboratory Assistant
Jeanette Shaw, M.S., Laboratory Technician
CHEMISTRY AND SOILS
R. V. Allison, Ph.D., Chemist**
R. W. Ruprecht, Ph.D., Chemist
R. M. Barnette, Ph.D., Chemist
C. E. Bell, Ph.D., Associate
R. B. F'rench, Ph.D., Associate
H. W. Winsor, B.S.A., Assistant
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural Economist**
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant
ECONOMICS, HOME
Ouida Davis Abbott, Ph. D., Specialist**
C. F. Ahmann, Ph.D., Physiologist
ENTOMOLOGY
J. R. Watson, A.M., Entomologist**
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist and
Acting Head of Department
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Horticulturist
R. J. Wilmot, M.S.A., Specialist, Fumigation
Research
R. D. Dickey, B.S.A., Assistant Horticulturist
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist**
George F. Weber, Ph.D., Plant Pathologist
R. K. Vorhees, M.S., Assistant
Erdman West, M. S., Mycologist
Lillian E. Arnold, M.S., Assistant Botanist
Stacy O. Hawkins, M.A., Assistant Plant
Pathologist
SPECTROGRAPHIC LABORATORY
L. W. Gaddum, Ph.D., Biochemist
L. H. Rogers, M.A., Spectroscopic Analyst


BOARD OF CONTROL
Geo. H. Baldwin, Chairman, Jacksonville
Oliver J. Semmes, Pensacola
Harry C. Duncan, Tavares
Thomas W. Bryant, Lakeland
R. P. Terry, Miami
J. T. Diamond, Secretary, Tallahassee

BRANCH STATIONS
NORTH FLORIDA STATION, QUINCY
L. O. Gratz, Ph.D., Plant Pathologist in
Charge
R. R. Kincaid, Ph.D., Asso. Plant Pathologist
J. D. Warner, M.S., Agronomist
Jesse Reeves, Farm Superintendent
CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Horticulturist in Charge
John H. Jefferies, Superintendent
W. A. Kuntz, A.M., Assoc. Plant Pathologist
Michael Peech, Ph.D., Soils Chemist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Asst. Entomologist
Walter Reuther, B. S., Asst. Horticulturist
EVERGLADES STATION, BELLE GLADE
A. Daane, Ph.D., Agronomist in Charge
R. N. Lobdell, M.S., Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
Thomas Bregger, Ph.D., Sugarcane Physiologist
G. R. Townsend, Ph.D., Assistant Plant
Pathologist
J. R. Neller, Ph.D., Biochemist
R. W. Kid-er, BS., Assistant Animal
Husbandman
Ross E. Robertson, B.S., Assistant Chemist
B. S. Clayton, B.S.C.E., Drainage Engineer*
SUB-TROPICAL STATION, HOMESTEAD
H. S. Wolfe, Ph. D., Horticulturist in Charge
W. M. Fifield, M.S., Asst. Horticulturist
Geo. D. Ruehle, Ph.D., Associate Plant
Pathologist

W. CENTRAL FLA. STA., BROOKSVILLE
W. F. Ward, M.S.A., Asst. An. Husbandman
in Charge*

FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Plant Pathologist in
Charge
W. B. Shippy, Ph.D., Asso. Plant Pathologist
K. W. Loucks, M. S., Asst. Plant Pathologist
J. W. Wilson, Ph.D., Associate Entomologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
Cocoa
A. S. Rhoads, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist
Monticello
Sam O. Hill, B.S., Asst. Entomologist
Bradenton
David G. Kelbert, Asst. Plant Pathologist
C. C. Goff, M.S., Assistant Entomologist
Sanford
E. R. Purvis, Ph.D., Assistant Chemist,
Celery Investigations
Lakeland
E. S. Ellison, Ph.D., Meteorologist*
B. H. Moore, A.B., Asst. Meteorologist*

In cooperation with U.S.D.A.
** Head of Department.










Development of
THE ROOT-KNOT NEMATODE ON BEANS

As Affected by Soil Temperature

By G. R. TOWNSEND


CONTENTS
Page
Introduction ............ ...... ............................................. .......... 3
Review of Literature ........ .............................. ........................... 3
Experimental Studies ..........--....... ..............-..... .............. 6
M materials and M methods ....................................................................... 6
R results ................................................... ........................................ 8
D discussion ........ .....................- ................. -.... ................... .................. 12
Sum m ary ....-...................................................... .... ................... ... 13
L literature Cited ............................... ........ ..... ......... ......................... 14


INTRODUCTION

The root-knot nematode, Heterodera marioni (Cornu) Goodey,
is found throughout the tropical and temperate regions of the
world. In the colder regions it is found only where it has been
introduced into greenhouse soils. At its most northern range in
the field soils of the United States H. marioni passes through only
one or two generations during the warmer months, and is inactive
throughout the remainder of the year. In the Southern states,
this nematode is active over a much longer period. Here, it may
pass through 10 or 12 generations a year. A consequence of
this prolonged activity is that very large nemic populations some-
times occur in the soils of the Southern states. Since the severity
of root-knot in any particular host plant is generally in pro-
portion to the numbers of nematodes invading its roots, the dis-
ease is usually more destructive in the Southern states than far-
ther north.
It is the purpose of this paper to record certain experiments
showing that the soil temperature has a controlling influence
upon rate of nematode development, and hence upon severity
of the root-knot disease of snap beans.

REVIEW OF LITERATURE
Temperature was recognized as an important factor in the
development of nematodes almost as soon as these pests were
proved to be the cause of root-knot. Neal (9)1 thought that the

IItalic figures in parentheses refer to "Literature Cited" in the back
of the bulletin.










Development of
THE ROOT-KNOT NEMATODE ON BEANS

As Affected by Soil Temperature

By G. R. TOWNSEND


CONTENTS
Page
Introduction ............ ...... ............................................. .......... 3
Review of Literature ........ .............................. ........................... 3
Experimental Studies ..........--....... ..............-..... .............. 6
M materials and M methods ....................................................................... 6
R results ................................................... ........................................ 8
D discussion ........ .....................- ................. -.... ................... .................. 12
Sum m ary ....-...................................................... .... ................... ... 13
L literature Cited ............................... ........ ..... ......... ......................... 14


INTRODUCTION

The root-knot nematode, Heterodera marioni (Cornu) Goodey,
is found throughout the tropical and temperate regions of the
world. In the colder regions it is found only where it has been
introduced into greenhouse soils. At its most northern range in
the field soils of the United States H. marioni passes through only
one or two generations during the warmer months, and is inactive
throughout the remainder of the year. In the Southern states,
this nematode is active over a much longer period. Here, it may
pass through 10 or 12 generations a year. A consequence of
this prolonged activity is that very large nemic populations some-
times occur in the soils of the Southern states. Since the severity
of root-knot in any particular host plant is generally in pro-
portion to the numbers of nematodes invading its roots, the dis-
ease is usually more destructive in the Southern states than far-
ther north.
It is the purpose of this paper to record certain experiments
showing that the soil temperature has a controlling influence
upon rate of nematode development, and hence upon severity
of the root-knot disease of snap beans.

REVIEW OF LITERATURE
Temperature was recognized as an important factor in the
development of nematodes almost as soon as these pests were
proved to be the cause of root-knot. Neal (9)1 thought that the

IItalic figures in parentheses refer to "Literature Cited" in the back
of the bulletin.










Development of
THE ROOT-KNOT NEMATODE ON BEANS

As Affected by Soil Temperature

By G. R. TOWNSEND


CONTENTS
Page
Introduction ............ ...... ............................................. .......... 3
Review of Literature ........ .............................. ........................... 3
Experimental Studies ..........--....... ..............-..... .............. 6
M materials and M methods ....................................................................... 6
R results ................................................... ........................................ 8
D discussion ........ .....................- ................. -.... ................... .................. 12
Sum m ary ....-...................................................... .... ................... ... 13
L literature Cited ............................... ........ ..... ......... ......................... 14


INTRODUCTION

The root-knot nematode, Heterodera marioni (Cornu) Goodey,
is found throughout the tropical and temperate regions of the
world. In the colder regions it is found only where it has been
introduced into greenhouse soils. At its most northern range in
the field soils of the United States H. marioni passes through only
one or two generations during the warmer months, and is inactive
throughout the remainder of the year. In the Southern states,
this nematode is active over a much longer period. Here, it may
pass through 10 or 12 generations a year. A consequence of
this prolonged activity is that very large nemic populations some-
times occur in the soils of the Southern states. Since the severity
of root-knot in any particular host plant is generally in pro-
portion to the numbers of nematodes invading its roots, the dis-
ease is usually more destructive in the Southern states than far-
ther north.
It is the purpose of this paper to record certain experiments
showing that the soil temperature has a controlling influence
upon rate of nematode development, and hence upon severity
of the root-knot disease of snap beans.

REVIEW OF LITERATURE
Temperature was recognized as an important factor in the
development of nematodes almost as soon as these pests were
proved to be the cause of root-knot. Neal (9)1 thought that the

IItalic figures in parentheses refer to "Literature Cited" in the back
of the bulletin.







Florida Agricultural Experiment Station


northern range of nematodes would not extend beyond the 50
F. isotherm in this country because the worms are "paralyzed by
cold". Atkinson (1) suggested that the 350 F. isotherm would be
the more probable northern boundary of their range since they
were known to be present in Scotland. Bessey (2) reported that
nematodes had become established in unprotected locations in
New York on ginseng and alfalfa, and in the Upper Peninsula
of Michigan. He observed nematodes infesting ginseng where
the soil had frozen to a depth greater than three feet, and on
peonies in Nebraska where the temperature sometimes reaches
-300 F. These observations convinced Bessey that cold alone did
not kill the nematodes. However, he did not believe that they
would become widely distributed in the Northern states.
Newhall (10) stated that "H. marioni has been on the increase
in the mucklands of New York during the past few years, prob-
ably due to the higher average temperatures which were exper-
ienced in the northeastern part of the United States". However,
he observed that "last winter's (1933-34) low temperatures evi-
dently reduced their numbers considerably". The temperature
had remained below -150 F. for 24 hours on one occasion during
that winter. Samples of soil from a field known to have been
infested during the preceding summer were collected and planted
to squash which developed no galls in eight weeks.
Cunningham (3) has reported on the occurrence of H. marioni
in potatoes on Long Island. He found that the nematodes were
capable of over-wintering in the field soils. The larvae were
found within the roots of the potato plants towards the end of
May. These nemas had matured and produced a second genera-
tion of larvae early in July. Tuber infections occurred as the re-
sult of the activity of the second and third generations of larvae.
Watson (14) reported that nematodes are least active in Flor-
ida during the cooler parts of the year. In the latitude of Gaines-
ville they generally do comparatively little damage between No-
vember 1 and April 1. Farther south they are more active in
the winter than they are at Gainesville. While studying the depth
to which nematodes occur in Florida soils, Godfrey (4) found the
nemic population considerably reduced in the winter at Brooks-
ville. Bessey (2), working at Miami, found no period of the
year when nematodes were inactive.
In 1926, Godfrey (5) reported his experiments on the effect
of temperature and moisture on H. marioni. It was his observa-
tion that the amount of moisture in the soil seemed to have little







Root-Knot Nematode on Beans


influence on root-knot, if there was sufficient moisture for the
growth of the crop. Root-knot galls were produced on plants
growing in soils having moistures less than 40 percent and
more than 80 percent of their water-holding capacity. Tempera-
ture was found to play a more important role in relation to
infection by nematodes. In a series of experiments with toma-
toes, cucumbers, tobacco, lettuce, celery, vetch and potatoes
growing at controlled soil temperatures he found that infections
were rare at 100 to 12 C. Few infections occurred in soils
cooler than 160 C. Above that temperature the number of
galls per decimeter of root length rapidly increased. With some
plants there seemed to be fewer galls at temperatures above 300
C. than a few degrees lower, although the galls were abundant at
the highest temperatures at which the plants would grow.
Jones (8) performed some experiments with tomatoes growing
at controlled soil temperatures and found that infections occurred
at all of the temperatures he used. The lowest temperature in
his experiment was 150 C. Galls were most numerous in pro-
portion to the size of the roots at 240 to 300 C.
Godfrey and Oliveira (6) demonstrated that there is an effect
of the host species upon the rate of development of nematodes.
Cowpeas and pineapples were inoculated and grown in a green-
house at 20 to 330 C. The period from inoculation to the matur-
ation of female nematodes was 19 days in the cowpea and 35
days in the pineapple. They suggested that this effect of the host
species may be related to the rate of development of the multi-
nucleate giant cells (nourishing cells) of the host.
Hoshine and Godfrey (7) have studied the effect of high tem-
peratures upon the survival of nematode larvae and eggs. They
reported that at 400 C. the larvae were killed in 2 hours and 7
minutes. The eggs in masses survived for 41/2 days at this tem-
perature. Death was instantaneous for larvae at 530 C., and for
eggs at 580 C.
Tyler (11), who studied the effect of temperature upon nema-
tode development in California, stated that development pro-
gresses between the temperatures of 500 and 900 F. At 81 F.
the rate of development was most rapid and the generation
time was 23 to 26 days. The same development at 580 F. required
115 to 122 days. She stated that freezing at 320 F. did not kill
the larvae, but that all were killed within two hours at 00 F.
The thermal death point for nematodes in the soil was said to be
1100 F. for a period of two hours.






Florida Agricultural Experiment Station


In a later paper Tyler (12) made a more exact study of the
thermal relations of H. marioni on the tomato plant. She showed
that the typical hyperbolic curve for a time-temperature relation-
ship becomes a straight line when platted as a rate-temperature
relationship. Rate was considered to be the reciprocal of gen-
eration time. By constructing a straight line graph from the
generation times of 279 nematodes grown in root cultures at
controlled temperatures she reached the conclusion that the min-
imum temperature for nematode development is 11.50 C. This
represents an average for that number of individuals, for the
development from gall formation to egg laying. However, she
showed with appropriate data that the minimum temperature
for the initial stages of development was close to 100 C. but that
no nematodes laid eggs at temperatures below 14.30 C. Twenty-
two records for individuals grown at temperatures above 280
C. showed a retarded rate of growth. Gall formation occurred
in cultures at temperatures as high as 350 C. but complete
development was not obtained above 31.50 C.
Tyler (12) also computed the hour-Centigrade units necessary
for the various stages of development of H. marioni on tomatoes.
These units were calculated by multiplying the degree Centigrade
above 100 C. by the duration of the exposure in hours. Thus,
she found that 500 hour-Centigrade units are needed for the
formation of visible galls; 3,700 to 6,000 units are needed to
bring about molting of the larval skins; 6,500 to 8,000 units
must accumulate before egg laying starts, and 11,500 to 13,000
units are needed for a complete life cycle.

EXPERIMENTAL STUDIES

Materials and Methods:-The experiments reported herein
have been a study of the thermal relationships of H. marioni as
related to the ability of this nematode to infect snap beans,
Phaseolus vulgaris, under field conditions. All of the work has
been done on a small plot of saw-grass peat soil at the Ever-
glades Experiment Station during the period 1934-1936.
In September 1934 a plot of soil five feet by five feet was laid
out and enclosed with a wooden frame placed so that soil would
not be moved either from or onto the plot. A double recording
soil thermograph was installed in a louvered shelter beside the
plot. One bulb was placed at a depth of three inches and the other
at six inches below the soil surface. Because of the similarity of
the mean temperatures at these depths only the three inch record







Root-Knot Nematode on Beans


has been used for this study. The accuracy of this instrument
was checked by comparisons at frequent intervals with the read-
ings of a standard laboratory thermometer. After the instru-
ment was first regulated it was seldom necessary to make other
adjustments.
A large population of H. marioni was established in the soil
by the addition of root-knot galls from okra, Hibiscus esculentus,
which contained the mature female nematodes, and embryonated
eggs. This population was maintained subsequently by allowing
each generation of nematodes to reach maturity and returning
some of the galled bean roots to the plot. No attempt was made
to ascertain how large this population was, although it was
evident that its numbers fluctuated, as indicated by the numbers
of infected plants which grew on the plots. The number of
nematodes was never so low that infection was not obtained.
An attempt was made to keep the soil moisture uniform by
applying water when the beans indicated a need for it. The
fluctuations in soil moisture which did occur probably had very
little influence on the nematodes, as Godfrey's (5) data would
suggest. Applications of chemical fertilizers were made on
several occasions to maintain the fertility of the plot. The other
environment factors were not subject to control.
Bountiful beans were grown on this plot of infested soil seven
times during the 1934-35 season and five times during 1935-36.
Two of the crops in 1934-35 failed before the nematodes com-
pleted their development. The data presented were obtained
from the 10 crops of beans on each of which a generation of
nematodes matured. The generations of nematodes have been
numbered in chronological order.
The procedure of the study has been to make an examination
of the roots of a few plants from the plot at sufficiently frequent
intervals to determine the stage of development of the nematodes.
The specimens were dissected in water under the microscope to
make a correct diagnosis. By this method all of the larval and
female stages were seen readily under the low power of a com-
pound microscope. Males have been seen occasionally but so
infrequently that it seems improbable they play an essential role
in the biology of this nematode. Tyler (13) has shown that
parthenogenetic reproduction occurs in this species.
The criteria used to determine the thermal relationships have
been (a) the generation time, and (b) the mean soil temperature
at a depth of three inches during the period o~f each generation.







Florida Agricultural Experiment Station


The generation time has been considered to be that period from
the occurrence of susceptible host tissue (primary roots) to the
occurrence of hatching eggs produced by nemas in these roots.
Obviously, this determination is subject to some errors since the
second point cannot be determined for the same plant that was
used for the first determination. The validity of the method rests
upon the assumption that representative samples were collected
for the examinations. Usually 10 or more plants were taken for
each examination.
The mean soil temperature has been considered to be the
average of the daily maximum and minimum temperatures. It
is reported in each generation for four phases of the life cycle,
i. e. (1) from the occurrence of primary roots to gall formation;
(2) from gall formation to the molting of the larval skins; (3)
from molting to the beginning of egg laying; (4) from egg
laying to the hatching of second generation larvae.
Results:-Data on records of the development of nematodes
through 10 generations, and the temperature of the soil at a
depth of three inches for the period of each generation have
been compiled. These data (Table 1) have been subjected to
statistical methods similar to those employed by Tyler (12) in
her study of the development of H. marioni under controlled tem-
perature conditions in the laboratory. From these calculations
there have been derived velocity curves which graphically present
the acceleration in the rate of growth of H. marioni on beans
as produced by rising soil temperatures. Also, a study was made
of the effects of the accumulated temperature upon the develop-
ment of the nematodes from free living larvae to the hatching of
second generation larvae.
A casual inspection of these records for 10 generations of
nematodes reveals at once the time-temperature relationship.
The nematodes matured much more quickly when the soil tem-
peratures were high than when they were low. By comparing
generations 3 and 5, it may be seen that an increase of 100 C. in
the mean soil temperature reduced the generation time from 64
to 24 days. Similarly, by comparing generations 6 and 8, an
approximate increase of 100 C. reduced the generation time 60
percent.
The direct relation of soil temperature to rate of development
of H. marioni is seen when the data are platted in such manner
that temperatures are expressed on the vertical axis, and rate of
development on the horizontal axis. Rate of development may








Root-Knot Nematode on Beans


TABLE 1.-EFFECT OF THE MEAN SOIL TEMPERATURE UPON FOUR PHASES
OF 10 GENERATIONS OF H. marioni.


Genera-
tion

1




2




3























8




9




10


To gall formation ...........
To molting ......................
To egg laying ................
To hatching ....................
Generation-time ...........
To gall formation ...........
To molting -..........-.......
To egg laying ....................
To hatching ...................
Generation-time ................
To gall formation .........
To molting ..................
To egg laying ..............
To hatching ...................
Generation-time .......-......
To gall formation ..........
To molting .......................
To egg laying ...................
To hatching ....................
Generation-time ...............
To gall formation ...........
To molting .....-.............
To egg laying ..................
To hatching ..................
Generation-time ................


Development from
free larvae

To gall formation ...........
To molting ...................
To egg laying ...................
To hatching .....................
Generation-time .........-...
To gall formation ...........
To molting ........................
To egg laying ..................
To hatching ......................
Generation-time ......---......
To gall formation ............
To molting .......................
To egg laying ....................
To hatching .....................
Generation-time ................
To gall formation ............
To molting ......................
To egg laying ...................
To hatching ......... .......
Generation-time .............
To gall formation ...........
To molting ........................
To egg laying ...................
To hatching ...................
Generation-time ........-......-


Mean
Dates Temperature
C.

9/17/34 27.26
9/22/34 27.03
0/ 1/34 28.03
0/ 5/34 26.50
27.38
0/20/34 25.25
0/29/34 25.56
1/13/34 23.53
1/21/34 20.12
23.47
1/21/35 20.55
2/15/35 17.58
3/ 2/35 19.54
3/13/35 22.78
19.54
4/ 3/35 27.37

4/22/35 25.09
4/29/35 24.98
25.60
5/ 7/35 29.34
5/16/35 29.60
5/23/35 29.73
5/27/35 28.86
S 29.48


9/30/35

10/ 9/35
10/14/35

11/ 6/35
11/14/35
11/23/35
12/10/35

1/ 6/35

2/17/36
3/ 3/36

3/19/36

4/10/36
4/13/36

5/ 5/36

5/20/36
5/25/36


28.09

26.42
25.09
27.08
24.36
24.45
22.72
21.46
22.74
16.74

17.88
17.76
17.56
21.29

25.55
25.06
24.29
27.54

26.82
23.25
26.19


1
1I

1
1
1
1


Days


4
5
9
4
22
4
9
15
8
36
13
25
15
11
64
8

19
7
34
4
9
7
4
24
16

9
5
30
5
8
9
17
39
20

42
15
77
10

22
3
35
4

15
5
24





-






Florida Agricultural Experiment Station


be expressed either as the reciprocal of generation-time, or as
generations per year. The reciprocal of generation-time is a
fractional expression for generations per day. When the coor-
dinates for temperature and rate of development are plotted
for the 10 generations the 10 points of convergence lie close to
a straight line. The point of origin and slope of such a straight
line have been calculated by the method of least squares.
When the reciprocals of generation-time (generations per day)
are plotted along the X axis and the temperatures on the Y
axis, it is found that the point of origin of a straight line through
the coordinates is at 14.750 C. (Fig. 1). The slope of the line is

So/7 30 -- --~ -- -- -- -- -- 0 .--
Temp 23 -
C 26 -- -/-
2 7 -- -
26 ---



/9 ----- --
2 4 -- -- -- -- -- -- --




/7.
17--
16 ---


APec,'o-/1r 0 005 .0/0 0/5 0OO .025 .030 .035 .040 .045 .0.
eCieryeO /185 365 548 73/ /.3 1096 1278 /46/ /6.44 1826
I9---- ---------------




Fig. 1.--Rate of development of Heterodera marioni on beans as influenced
by the soil temperature.

such that it rises 3.1590 C. for each 0.01 division on the hori-
zontal axis. By substituting generations per year on the X axis
it is found that a rise of 0.86480 C. increases the generations per
year by one.
The cumulative effect of soil temperature upon the develop-
ment of the root-knot nematode has been determined from a
study of the data in Table 1. A serviceable measure of accumu-
lated temperature was found in the computation of hour-Centi-
grade units. These units have been calculated from the base of
12o C. The assumption is made that development is negligible
at temperatures lower than this and proceeds as a function of
the product of hours by Centigrade degrees above 120 C. Thus,
for a temperature of 200 C. there would accumulate 192 hour-







Root-Knot Nematode on Beans 11

TABLE 2.-THE HOUR-CENTIGRADE UNITS NECESSARY FOR THE DEVELOP-
MENT OF H. marioni ON Phaseolus vulgaris.

Number of units from free living larvae to
Generation Gall I Hatching
Formation Molting I Egg laying eggs

1 1,465 3,269 6,731 8,123
2 1,272 4,201 8,352 9,911
3 2,668 6,010 8,730 11,576
4 2,951 -8,920 11,101
5 1,665 5,467 8,446 10,065
6 6,178 9,293 10,864
7 1,483 3,875 6,191 10,056
8 2,275 8,202 10,276
9 2,230 -9,384 10,324
10 1,492 -6,827 8,177

Means ...................... 2,367.9 4,563.6 8,107.6 10,047.9

Standard deviation
for single result 1,380 1,021 1,071 1,071

Standard deviation
of mean .............. 436 456 339 339

Significant depart-
ure for single
result ................- 2,979 2,205 2,311 2,311

Significant depart-
ure from mean
value ............. .... 942 985 732 732
Centigrade units for each day on which that temperature pre-
vailed. Computations based upon this assumption have been
made from the data in Table 1 and are presented in Table 2.
There is only one significant departure from the mean values
shown in Table 2. The value of 6,178 hour-Centigrade units for
gall formation in generation 6 is somewhat higher than would be
expected on the basis of the mean value for the 10 observations.
An explanation will be offered for this in the discussion.
It is shown in Table 2 that the development of galls on the
roots of beans by H. marioni required 2,368 436 hour-Centi-
grade units. To carry the development to the molting of larval
skins 4,564 456 hour-Centigrade units were required. Eggs
were first deposited by the mature females after 8,108 339
units had accumulated. The development from larvae to larvae
took 10,048 339 hour-Centigrade units.







Florida Agricultural Experiment Station


DISCUSSION
Data obtained in this study support the observations of other
workers that temperature has an important effect upon the
development of H. marioni. Where the soil is cool in the winter
development ceases or progresses very slowly. Consequently, in
the cooler soils there are fewer generations each year and the
population of nematodes does not reach the high numbers which
occur in infested soils of the Southern states, particularly during
the period from March to October.
The potential maximum seasonal population of H. marioni is
extremely high, since each generation raises the population by a
power of the basic reproductive coefficient2. Barring limiting
factors the progeny of one nematode may be expected to increase
as 100 : 1002 : 1003 : 1004 : 1005 during the course of five gen-
erations. Were it not for limitations exerted by lack of food,
or the presence of enemies, the thermal relationship in the South-
ern states is favorable for the production of 10 billion or more
nematodes for each nematode present at the beginning of the
season. In southern Florida where nemic development seldom
ceases the problem becomes acute in infested soils.
The calculations of the effect of temperature upon the rate of
development have shown that for these observations the mean
minimum temperature at which complete development occurs
on beans is 14.750 C. This point is 3.250 C. higher than Tyler
found for H. marioni on tomatoes with constant graded tempera-
tures.
There are several reasons to account for this difference be-
tween the minimum temperatures for development as found by
Tyler and the author. She selected her data to the extent that
the slowest individuals were eliminated from consideration.
While this may be valid for a theoretical consideration of the
lowest temperatures permitting development, it does not repre-
sent the condition in the field where the statistical average of all
the rates in a population of millions of individuals should be
considered. An approach to this method of consideration was
made in the present study, although the number of generations
studied is few. However, the statistical analyses of the data

2The term basic reproductive coefficient may be defined as the average
number of nematodes hatching from the eggs laid by one female. Various
investigators have given the number of eggs laid per female as from 60
to 2,000. Tyler (12) counted 1,406 larvae which hatched from 1,998 eggs
laid by one female. The value of 100 here assigned to the reproductive
coefficient is purely arbitrary and is thought to be a conservative figure.







Root-Knot Nematode on Beans


on the cumulative effects of temperature do not suggest that the
mean values determined for 10 generations would be altered
appreciably in repetitions of the studies.
It has been shown by Godfrey and Oliveira that the generation-
time of H. marioni on pineapples is much longer than on cowpeas
grown at the same temperatures. Since generation-time is one
of the two variables entering into the calculation of the velocity
curves, it follows that the point of origin of these curves does
not necessarily fall at the same temperature for different host
species.
Another explanation for divergent results may be that there
are physiological races of H. marioni and that one adapted to
the latitude and temperatures of California would develop at
lower temperatures than a race from Florida.
It is probable that the minimum temperature at which develop-
ment can occur is somewhat lower than is shown by velocity
curves because this gives a mean value for all of the observations.
Had the curve been constructed on the basis of the observations
below 200 C. the point of origin would have been nearer 120 C.
This would indicate that near the minimum temperature for
development a slight change in temperature may bring about a
greater development than the same change when it occurs at
higher temperatures.
The base of 120 C. used for calculating the cumulative effects
of temperature was chosen for the reasons that the velocity
curves do not indicate that a lower value would be more prob-
able, and that the mean values for hour-Centigrade units showed
the least variability when calculated from this temperature. The
assumption that development is negligible at temperatures below
120 C. is sustained by all of the data. At temperatures above
120 C. the development of H. marioni is directly proportional to
hour-Centigrade units. In this way the generation-time for the
root-knot nematode on beans becomes a function of soil tem-
perature. Where the mean soil temperature for the year is 200
C. six generations would be expected if susceptible host plants
are continuously present. For mean soil temperatures of 250 C.
and 300 C. the number of generations expected in a year would
be 12 and 18, respectively. In sections of the United States where
the mean soil temperature is as low as 160 C. only one or two gen-
erations of the root-knot nematode would be expected each year.
In southern Florida the mean soil temperature is near 250 C.







Florida Agricultural Experiment Station


Here, 10 or 12 generations would be expected where susceptible
host plants are always present.
The mean value for the number of hour-Centigrade units
necessary for complete development of H. marioni on beans was
determined to be 10,048 units with a standard deviation of 339
units. It would be expected that the mean values would occur
between 9,300 and 10,800 units in any repetition of these experi-
ments, where the base temperature is 120 C.
A significant departure from the expected value for the units
necessary for gall formation was noted in generation 6. This
seemed to be explained by the fact that the nematode population
on the plot was quite low when this generation was studied. The
population had been reduced by the failure of a crop of beans
in June 1935 before the nemas were mature. During the summer
the plot was fallow and excessive soil temperatures occurred.
In August the soil temperature exceeded 400 C. for 14 hours and
reached 420 C. for two hours. These temperatures must have
been fatal to the larvae and some of the egg masses in the surface
three inches of the soil. When beans were planted on the plot
in September no galls were found on their roots for 16 days,
although five examinations were made during that period. There
is, therefore, some uncertainty as to the value of this determi-
nation because of the low population of nemas. However, enough
nemas matured on the plot in the sixth generation to insure a
plentiful supply of eggs for the continuation of the study in the
later generations.

SUMMARY
A study of the effects of soil temperature upon the activity
of H. marioni on snap beans was made under field conditions.
The rate of development of this nematode was found to be a
function of temperature.
Development at mean temperatures below 14.750 C. would not
be expected, although some may occur as low as 120 C.
The number of generations per year increases with the tem-
perature, consequently 10 or 12 generations per year are possible
in southern Florida.
About 10,000 hour-Centigrade units above 120 C. are required
for the development of each generation.








Root-Knot Nematode on Beans 15

LITERATURE CITED
1. ATKINSON, G. F. Nematode root-galls. Ala. Agr. Exp. Sta. Bul.
(n. s.) 9. 1889.

2. BESSEY, E. A. Root-knot and its control. U. S. Dept. Agr. Bur. Plant
Indus. Bul. 217. 1911.

3. CUNNINGHAM, H. S. The root-knot nematode (Heterodera marioni)
in relation to the potato industry on Long Island. N. Y. Agr. Exp.
Sta. Bul. 667. 1936.

4. GODFREY, G. H. The depth and distribution of the root knot nematode
in Florida soils. Jour. Agr. Res. 29: 93-98. 1924.

5. Effect of temperature and moisture on nematode root
knot. Jour. Agr. Res. 33: 223-254. 1926.

6. GODFREY, G. H., and J. OLIVEIRA. The development of the root-knot
nematode in relation to root tissues of pineapple and cowpea. Phy-
topath. 22: 325-348. 1932.

7. HOSHINO, H. M., and G. H. GODFREY. Thermal death point of Hetero-
dera radicicola in relation to time. Phytopath. 23: 260-270. 1933.

8. JONES, L. H. The effect of environment on the nematode of the tomato
gall. Jour. Agr. Res. 44: 275-285. 1932.

9. NEAL, J. C. The root-knot disease of the peach, orange and other
plants in Florida, due to the work of Anguillula. U. S. Dept. of
Agr. Div. Ent. Bul. 20. 1889.

10. NEWHALL, A. G. Root knot nematode population in New York reduced
by cold weather. Plant Dis. Rept. 18: 111. 1934.

11. TYLER, JOCELYN. The root-knot nematode. Calif. Agr. Exp. Sta.
Circ. 330. 1933.

12. Development of root-knot nematode as affected by
temperature. Hilgardia 7: 391-415. 1933.

13. Reproduction without males in aseptic root culture of
the root-knot nematode. Hilgardia 7: 373-388. 1933.

14. WATSON, J. R. Control of root-knot. II. Fla. Agr. Expt. Sta. Bul.
159. 1921.




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