Population dynamics M. incognita and R. reniformis: Thomas, Clark 211
15. Jenkins, W. R. 1964. A r a p i d c e n t r i f u g a l
flotation t e c h n i q u e for s e p a r a t i n g n e m a t o d e s from
soil. P l a n t Dis. Rept. 48:692.
16. Kheir, A. M., a n d A. A. O s m a n . 1977. Interaction of Meloidogyne incognita a n d R o t y l e n c h u l u s
r e n i f o r m i s on tomato. Nematol. Medit. 5:113-116.
17. Krusberg, L. R., a n d I,. W. Nielsen. 1958.
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Rico variety of sweet potato. P h y t o p a t h o l o g y 48:
30-39.
18. Linford, M. B., a n d J. M. Oliveira. 1940.
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7:35-42.
19. Martin, ~:. J., w . Birchfield, a n d T. P. Hernandez. 1966. Sweet p o t a t o varietal reaction to the
r e n i f o r m n e m a t o d e . P l a n t Dis. Rept. 50:500-502.
20. Nielsen, L. W., a n d J. N. Sasser. 1959. Control of root-knot n e m a t o d e s affecting Porto Rico
sweet potatoes. P h y t o p a t h o l o g y 49:135-140.
21. Ogle, W . L. 1952. A s t u d y of factors affecting cracking of t h e storage roots of the sweet
potato, I p o m o e a batatas Poir. Ph.D. T h e s i s , Univ.
of M a r y l a n d .
22. Singh, N. D. 1973. P r e l i m i n a r y r e p o r t of
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crops in T r i n i d a d . N e m a t r o p i c a 3:56-61.
23. ,tSngh, N. D. 1976. Interaction of Meloi-
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soybean. N e m a t r o p i c a 6:76-81.
24. T a h a , A. H. Y., a n d A. S. Kassab. 1979. T h e
histological reactions of Vigna sinensis to separate
a n d c o n c o m i t a n t parasitism by Meloidogyne javanica attd R o t y l e n c h u l u s reniformis. J. N e m a t o l . 11:
117-123.
25. T a h a , A. H. Y., atnl A. S. Kassab. 1980.
I n t e r r e l a t i o n s between Meloidogyne javanica, Rotyl e n c h u l u s reniformis, attd R h i z o b i u m sp. o n Vigna
sinensis. J. Nematol. 12:57-62.
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identification a n d control of root-knot n e m a t o d e s
(Meloidogyne species). Raleigh, N o r t h Carolina:
North C a r o l i n a State University Graphics.
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reniformis: A g r i c u h u r a l implications. P l a n t Dis.
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28. T h o m a s , R. J., a n d C. A. Clark. 1980. Interactions between Meloidog)/ale incognita a n d Rotyl e n c h u t u s r e n i f o r m i s on sweet potato. J. Nematol.
12:239 (Abstr.).
29. T h o m a s , R. J., attd C. A. Clark. 1981.
Meloidogyne incognita a n d R o t y l e n c h u l u s reniformls interactions in a sweet potato field. Phytop a t h o l o g y 71:908. (Abstr.).
Parasitism of Rotylenchulus reniformis onSoybean Root
Rhizobium Nodules in Venezuela
J. A. MEREDITH, 1 R . N . INSFRRA, ~ D. M o N z o N DE FERNANOEZ1
J o u r n a l of N c m a t o l o g y 15(2):211-214. 1983.
Rotylenchulus reniformis Linford and
Oliveira parasitizes soybean Glycine max
(L.) Merr. in Venezuela and is often associated with Pratylenchus brachyurus. In the
tropical climate of Venezuela, R. reniformis
reproduces rapidly on soybean roots; the
nematode also infects the Rhizobium root
nodules. Since there is no report of R. reniformis infection of soybean Rhizobium root
nodules, a histological study was made to
determine the effect of parasitism of nodules
by a Venezuelan population of M. renifo~'mis.
Soybean cv. Jupiter roots infected with
R. renifo~'mis were collected from a field
Received for publication 26 April 1982.
1Professor of Nematology and Graduate Student. respectively. Universidad Central de Venezuela, Facultad de
Agronornia, Instituto de Zoologia Agricola, Apartado 4579,
Maracay, Aragua 2101, Venezuela.
~Nematologist. Istituto Nematologia Agraria, CNR,
Bari. Italy. Present address: Crops Research Laboratory.
Utah State University, UMC 63, Logan, UT 84322,
in Portuguesa State. Roots were washed,
aud some were stained with acid fuchsin
in hot lactophenol and examined microscopically. Other roots with Rhizo.bium
nodules infected by mature nematode females were fixed in FAA (23% formalin,
3% acetic acid, 30% ethyl alcohol, 44%
distilled water), dehydrated in T B A (tertiary butyl alcohol), and embedded in paraffin. Cross sections 10-15 /~m thick were
stained with safranin fast-green, m o u n t e d
in D u m m a r xylene (3) and observed with
a compound microscope.
RotyIenchulus reniformis parasitized
both the roots and the Rhizobium nodules
of Jupiter soybean. T h e swollen posterior
portion of the females and egg masses protruded from the root nodule surface (Fig.
I). T h e female nematodes were observed
most frequently in the portion of the bacterial nodule in contact with the root, but
zie
ot X ,,,a oZogy.
5, No. 2, Apriz
[ l. rl
Figs. 1-2. Rotylenchns reniformis on soybean (Glycine nmx) root nodule. Scale bars = 480 #m. 1)
M a t u r e female (N) with the body posterior p o r t i o n protrucling f r o m tile root n o d u l e surface; E = egg
mass. 2) M a t u r e females (N) in the interstitial fissures of r u p t u r e d n o d u l e surface.
any point o[ the root nodule surface was
susc~t~tible to the nematode penetration.
Some females with egg masses were located
in the interstitial fissures of the ruptured
nodule surface (Fig. 2). T h e n u m b e r of mature females with egg masses averaged from
one to three per nodule.
Sections of nematode infected soybean
nodul.es showed that R. reniformis pene-
trated into the epidermis, root cortex, an6
nodule cortex and established a permanent
feeding site in the nodule endodermis and
the bundle endodermis (Figs. 3,4). T h e
most common reaction to the nematode in
the nodule vascular bundles was safranin
positive stained bundle endodermal cells
and accentuated hypertrophy of the bundle
sheath cells compared with the bundle
\\\\\
//z'i/
g-
Figs. 3-5. Histological alterations caused by t~otylenchulus reni]ormis ill soybean root nodules. Scale
bars = 71 /~m. 3) Cross section s h o w i n g a n e m a t o d e (N) p e n e t r a t e d into t h e root cortex (re) a n d feeding in the b u n d l e e n d o d e r m i s (be) of a vascular b u n d l e . Note the h y p e r t r o p h y of t h e b u n d l e s h e a t h
ceils (hs) c o m p a r e d u~ those of u n i n f e c t e d b u n d l e (ub); BA ~ bacteroid region, nc = n o d u l e cortex,
sne ~ suberized n o d u l e e n d o d e r m i s . 4) Cross section s h o w i n g a n e m a t o d e (N) feeding in the n o d u l e
e n d o d e r m i s (hen). Note the necrosis (ne) of n o d u l e e n d o d e r m a l (nen) a n d n o d u l e cortical (nc) cells
at the n e m a t o d e feeding site; BA = bacteroid region, rc ~ root cortex. 5) Cross section s h o w i n g a
n e m a t o d e (N) feeding in a n o d u l e cortical (nc) cell adiacent lo t h e bacteroid region (BA). Necrosis (ne)
is e v i d e n t in the n o d u l e cortical cell at t h e f e e d i n g site.
Rotylenchulus oll Soybean Nodules: Meredith et al. 213
214 Journal of Nematology, Volume 15, No. 2, April 1983
sheath cells of healthy vascular bundles
(Fig. 3). Accentuated necrosis (safranin
stained tissue) was also observed in the
nodule endodermal cells in direct contact
with the nematode head (Fig. 4). in some
cases, nematode specimens penetrated the
root and nodule cortex and reached the
innermost layer of nodule cortical cells
free of rhizobial infections and adjacent to
the bacteroid region (Fig. 5). Considering
that all the sectioned nodules were infected
with mature females only, this would indicate that R. reniformis was able to develop
by feeding in the nodule cortical cells of
soybean. However, there was no evidence
of nematode penetration into the bacteroid
region.
In addition to R. reniformis, Meloidogyne incognita is able to reproduce in soybean root nodules (2). But soybean root nodules are unfavorable for the development of
Heterodera glycines (1). H. glycines and
M. incognita both attack the vascular bundles, damaging the vascular elements by
inducing syncytium and giant cells formation, respectively (1,2), whereas R. reniformis caused alterations of the periphery
of vascular bundles, damaging the bundle
endodermis and inducing hypertrophy of
bundle sheath cells.
Tile adverse effect of R reniforrnis on
Rhizobium nodule production has been reported in cowpea (4), but from our observations on soybean root nodules there was
no evidence of bacteroid disruption by
R. reniformis. R. reni[ormis-infected soybean root nodules did not differ in size and
shape from healthy ones. T h e necrosis induced by the nematode in the endodermal
layers and also in the nodule and root
cortex may predispose the nodular tissues
to the infections of other pathogens and to
their consequent premature breakdown.
LITERATURE
CITED
1. Barker, K. R., D. Huisingh, and S. A. Johnston. 1972. Antagonist interaction between Heterodera glycines and Rhizobium japonicum on soy.
bean. Phytopathology 62:1201-1205.
2. Barker, K. R., and R. S. Hussey. 1976. Histopathology of nodular tissues of legumes infected
with certain nematodes. Phytopathology 66:851-855.
3. Johansen, D. A. 1940. Plant microtechnique.
New York: McGraw-Hill.
4. Taha, A. H. Y., and A. S. Kassab. 1980. Interrelations between Meloidogyne javanica, Rotylenchulus renifi~rmis, and Rhizobium sp. on Vigna
sinensis. J. Nernatol. 12:57-62.