Mechanisms Of Sorghum Resistance To The Spotted Stalkborer, Chilo Partellus ( Swinhoe) Lepidoptera Pyralidae
Abstract
Stalkborers are some of the most important pests
of cereal crops in the tropics and in particular the
semi-arid areas. Chilo partellus, the spotted
stalkborer, is one of the most notorious pests of
sorghum in that it occurs in almost all the areas
where sorghum is grpwn in the semi-arid regions of
Asia and Africa. Lately it has been found that this
pest is gradually increasing its range and importance.
Of the various sorghum pest control methods
available in the semi-arid regions none holds better
prospects than the use of resistant varieties. In this
study several experiments were conducted to elucidate
the mechanisms of resistance of different sorghum
cultivars and also to propose ~he methodology for
mechanisms of resistance studies. Accordingly five
criteria were used - for explaining these mechanisms.
These criteria were : Ca) Preference or Non-preference
for oviposition of the moth on different sorghum
cultivars, Cb) Larval establishment of Chilo partellus
larvae
first instarl on different sorghum cultivars,
Cc) Relative leaf damage and stem tunnelling in
different sorghum cultivars by C. partellus larvae,
Cd) Biophysical and preJimary biochemical studies
that elucidate the differences in cultivar
susceptibility to partellus, and (e) studies on
different cultivar tolerances to C. partellus damage.
The oviposition preference studies revealed that
sorghum cultivars differedm their suitability as a
C. partellus oviposition substrate. Cultivar IS 2205
was the least preferred while IS 18363 was the most
preferred. Experiments to identify the factors
responsible were inconclusive. Evidence pointed to
both biochemical and biophysical factors.
First instar larval establishment studies were
also inconclusive even though it was d~mostrated that
larval establishment was different among the cultivars
used. The only definit€ evIdence for poor establishment
in-some cultivars was biophys-ical.
Different cultivars were significantly different
in their susceptibility to leaf damage. The tendency
to form deadheirts was also significantly different.
But reasons for these differences were not apparent.
Cultivars were not significantly different in their
susceptibility to tunnelling even though they had
different amounts of fibre, lignin and sucrose.
The single most important factor for the different
cultivar susceptibilities was in their different
tolerances to C. partellus attack. Tillering, in
particular, was demonstrated to play an important role
in compensation for damage. The ability to flower and
to produce seed inspite of having a high infestation
were also very significant. Susceptible cultivars
dried up before they had flowered. Others still,
flowered but could not form seed. Using tolerance as
a criterion for resistance showed IS 18520 to be the
most resistant. Formation of multiple heads was also
shown to be an important factor.
Different cultivars had varying effects on the
development of f.. p.arte:!)us(ant ibiosis) . However, the
antibiotic effect was either insignificant or only just
significant statistically
Citation
Greenman Themba Masina (1980). Mechanisms Of Sorghum Resistance To The Spotted Stalkborer, Chilo Partellus ( Swinhoe) Lepidoptera Pyralidae). A thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy in the University of Nairobi, Department of Zoology.Publisher
University of Nairobi School of Biological Sciences,