| dc.description.abstract | Field, laboratory, and greenhouse experiments
were carried out to study e££ect o£ nematicide
application on bean (Phaseolus vulgaris) yields in
Kenya; penetration o£ larvae ot:' Meloidogyne incognita
and M. javanica in 6 bean varieties, and the
subsequent development ot:' the nematode parasites
within the hosts; and histopathology o£ the roots ot:'
the hosts in£ected with the two parasites.
The nematicides were applied to a dark-red
t:'riablecLay soil heavily in:f'es ted with the two roo tknot
nematod'e species, at Kenya Canners Plantation
Ltd., and Kuraiha Estate, Thika. It was t:'oundthat,
in the t:'irstt:'ieldexperiment at Kenya Canners
Plantation Ltd., application ot:' D-D as a broadcast
(overall) and a row treatment, and EDB applied as
a broadcast treatment, signit:'icantlyreduced the
number ot:' M. incognita and~. javanica larvae in the
soil. EDB row treatment did not reduce larval
populations. Signit:'icantyield increases (45-60%)
were obtained with Kikara and Mexico 142 with broadcast
and row application ot:' D-D, and broadcast application
ot:' EDB. This is consistent with the larval population
decreases in these treated plots. Nematicides did not
increase the yield ot:' Marathon green bean. Yields ot:'
this variety were unit:'ormlylow, presumably because the
soil type was not conducive to good growth. In the
second field experiment at Kuraiha Estate, D-D in the
planting row did not significantly increase the yield
of Kikara but a significant yield increase (32%) was
obtained with Mexico 142. These results indicate that
root-knot nematodes, in large numbers can reduce bean
yields in Kenya by as much as 60%.
In the preliminary laboratory and greenhouse
experiments, non-freshly-hatched larvae of M. incognita
and M. javanica, at inoculum .levels of 100 larvae,
failed to penetrate root systems of Kikara, Mexico 142,
Canadian Wonder, Masterpiece, Marathon, and Premier
bean varieties after exposure periods of 12, 24, or
48 hours. When the exposure period was increased to
48 hours, penetration of 5 of the 6 bean varieties
by freshly-hatched larvae of the nematode parasites
occurred at inoculum .levels of 100, 150, 200 and
300. In Mexico 142, even at the inoculum level of
300 larvae, there was no penetration. Although larvae
of the nematode parasites penetrated root systems
in all 6 bean varieties, results showed that, when
the experiment was conducted under .lowand variable
room or greenhouse temperature conditions, no
significant differences in penetration percentage
existed between the varieties and the species. Results
of a similar experiment conducted under controlled
growth chamber conditions at higher temperatures
indicated that highly signiricant dirferences at 0.1%
level occurred between the two species. At temperatures
of 2Jo and 29°C ror night and day respectively, M.
incogni ta .larvae penetrated root systems in a.LL the
6 bean varieties in signiricantly greater numbers
than~. javanica larvae. When the temperatures were
raised to 250 and JOoC ror night and day r-e spect.Lve.Ly ,
significantly higher numbers or M. incognita larvae
penetrated root systems of Kikara, Canadian Wonder,
Masterpiece, Marathon, and Premier than M. javanica
larvae. There were no significant differences between
~. incognita and Mo javanica larvae in penetration of
root systems of Mexico 142.
Within the hosts, it was found that rates of
development rrom larvae to sexually dirferentiated
nematodes occurred more rapidly in Mexico 142 for
M. incognita and M. javanica, and in Masterpiece for
M. javanica only, than in other bean varieties
inoculated at the same time. However, the period
taken for larvae of both nematode species to develop
to the adult stage was identical in all 6 bean
varieties. At growth chamber ambient temperatures
of 25°C and JOoC night and day respectively, a high
percentage or both species developed into females
which laid eggs within 20 days after inoculation;
these females completed their life cycle and a second
generation was developing within 30 days in all
varieties. A low percentage or the nematode species
developed to males. It is concluded rrom this study
that M. incognita and M. javanica can develop and
reproduce rapidly on Kikara, Mexico 142, Canadian
Wonder, Masterpiece, Marathon, and Premier bean
varieties; hence, the varieties are highly suitable
hosts or both nematode species. Under optimum
temperature conditions ror rapid development or both
species, at least 3 generations are possible on these
bean varieties in any or the growing seasons in East
Af'rica.
-Results' or the histopathological studies revealed
extensive damage to the cortical and vascular tissue
or roots of' the 6 ,bean varieties inrected with M.
incognita and M. javanica. These studies showed that
all 6 bean varieties were highly susceptible to both
nematode species; the nematodes red in the vascular
area and caused the f'ormation or 3-20 multinucleate
giant cells around a single f'emale. It was also shown
that disruption of' the stele by the giant cells,
prolirerated parenchyma cells, and the parasites
themse.lves caused the conducting tissues to be
scattered, so that, in cross section, the phloem and
xylem occurred in irregular patches rather than in
one continuous column. While most or the giant cells
were f'ound in the vascular cylinder in all 6 bean
varieties, giant cells were also observed in the cortex
or between the pericycle and endodermis in Mexico 142,
Canadian Wonder, and Premier bean roots.
A type of' tissue designated "abnormal xylem",
.which is characterized by secondary wall thickenings
of annular, reticulate, or pitted types, was observed
associated with giant cells.
No nuclear division was observed in giant ce.lls
in ·this study in any roots of' the bean varieties; it
was assumed that nuclear division in giant cells was
either not occurring at the time the tissues were killed
and fixed, or did not exist in the root cells of' the bean
varieties. | en |
