Prot, Jean-Claude

Van Gundy, S.D.

Horizon / Pleins textes

312 Journal of Nematology, Volume 11, No. 4,  October I979 
similis, Pratylenchus cofleae, Helicotylen- 
chus spp., and Meloidogyne spp. Fungi were 
obtained from 1,834 of 4,338 isolations from 
bananas. Four fungi occurred in 71% of 
the isolations from nematode lesions. They 
were: Acremonium stromaticum 2276, 
Fusarium solani lS%, Cylindrocarpon 
musae 17%, and Fusarium moniliforme 
14%. Apparently these fungi are part of the 
root and rhizome flora of bananas through- 
out the world. Nematode-fungus associa- 
tions on plantains were studied only in 
Honduras. Isolations were generally made 
from lesions caused by Pratylenchus cofleae, 
the nematode encountered most frequently 
on plantains. The fungi associated with 
nematode lesions on plantains are the same 
ones found on bananas. Fungi were ob- 
tained from 170 of 428 isolations. Acremon- 
ium stromaticum and Cylindrocarpon 
musae were recovered from 74% of the 
isolations.-Division of Tropical Research, 
United Fruit Company, La Lima, Hon- 
duras, Central America. 
PLATZER, E. G. Phosphoenolpyruvate 
metabolism and oxidoreductase reac- 
tions in Mermis nigrescens. 
The nature of phosphoenolpyruvate 
metabolism and cytoplasmic oxidoreductase 
reactions was investigated in Mermis 
nigrescens. Parasitic stages of M. nigrescens 
were obtained 14, 16, 21, and 30 days post- 
infection, and postparasites were obtained 
16 and 40 days postemergence from locusts 
(Sch ¿stocerca gregaria). The characteris tics 
of pyruvate kinase (PK), phosphoenolpy- 
ruvate carboxykinase (PEPCK), lactate 
(LDH), and malate dehydrogenases (MDH) 
were determined in homogenates of para- 
sitic nematodes. In general, the pH optima, 
substrate, cofactor and ion requirements, 
and apparent affinity constants of these 
enzymes were similar to those reported for 
other eukaryotic organisms. The specific 
activity of MDH remained constant in all 
stages of the nematode, whereas LDH activ- 
ity declined precipitously to very low levels 
in 21-day parasites and postparasites. This 
finding indicates that MDH is primarily 
responsible for maintenance of the cyto- 
plasmic redox state in maturing parasitic 
and postparasitic stages of M .  nigrescens. 
PK activity declined slightly during nema- 
tode development within the host, and 
upon emergence. PEPCK activity was not 
detectable in 14-day parasites, but it ap- 
peared by 19 days and remained at low 
levels in the parasitic and postparasitic 
stages. The low PEPCK activity suggests 
that CO, fixation is of little importance in 
M .  nigrescens, although further metabolic 
studies are necessary to substantiate the 
supposition.-Departm.en,t of Nematology, 
University of California, Riverside;. Cali- 
fornia 9252I. 
PROT, J.C., and S .  D. VAN GUNDY. The 
eflect of clay particles on the migration 
of  Meloidogyne incognita toward and 
into tomato roots. 
The effect of four soil types on the at- 
traction and migration of M .  incognita 
juveniles toward tomato roots was tested in 
20-cm PVC columns attached to Styrofoam 
cups and separated from the root system by 
a 35-pm screen. Only the juveniles that had 
migrated 20 cm and penetrated the roots in 
7 days were counted in roots stained with 
0.05% cotton blue. About 300 juveniles, 
not more than 24 li old, were introduced 
into the soil at the bottom of the column. 
The experiments were repeated three times, 
five replications per experiment, and main- 
tained at 26 C in a growth chamber with 
12-11 illumination. The percent juveniles 
found were respectively < I % ,  35%, 25%, 
and < I %  in roots grown in: a) silica sand 
composed of 250-pm particles; b) silica sand 
with 5% clay (modeling clay) added and 
thoroughly mixed; c) silica sand with 10% 
clay; and d) silica sand with 5% clay as a 
layer a t  the bottom of the cup but not be- 
tween the roots and the nematodes. If the 
juveniles were introduced directly around 
the roots growing in silica sand, about 70% 
of the juveniles penetrated the roots. It is 
hypothesized that the clay particles added 
to silica sand aid in the attraction of root- 
knot juveniles over long distances to plant 
roots by adsorbing and holding some root 
exudate, which helps the nematodes locate 
the roots by sensory perception.-De- 
partment of Nematology, University of 
California, Riverside, California 92521. 
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The effect of clay particles on the migration of Meloidogyne incognita toward and into tomato roots

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