Sorghum Diseases in India

easily identified than ergot resistance. Resistance
is probably dominant and probably controlled
largely by one or a few genes (Yadav
1974; Phookan 1987). The tr gene that removes
styler branches is reported to confer a high level
of resistance to smut (Wells et al. 1987), but the
same gene apparently confers greater susceptibility
to rust- At ICRISAT Center, several
composites have moderate to high levels of resistance,
and success has been achieved in
breeding smut-resistant varieties and synthetics.
There is a high probability for success in the
breeding of smut-resistant hybrids (Thakur and
Chahal 1987). Under experimental field conditions,
dwarfs seem to have more smut than do
the tall or medium-tall types, and panicles with
good exertion generally have less smut than
those with poor exertion. Ergot resistance almost
assures smut resistance, but the reverse is not true.
A pollen-based mechanism is reported to be operative
for smut resistance (Thakur et al. 1983b), but it
appears that in comparison with ergot, the smut
fungus requires more time from inoculation to infection
of the ovary. Therefore, smut-resistant genotypes
can probably tolerate a longer protogyny
period than can ergot-resistant genotypes. Multilocational
testing in India and western Africa, and
additional tests at ICRISAT SAT Center, have not
given evidence for the existence of pathotype differences
in T. penicillariae.
More research is needed to clarify the infection
process, including the nuclear status of infective
mycelium, and to precisely understand
the environmental conditions that favor the disease.
Additional information on the inheritance
of resistance would be useful, although current
breeding for resistance stands a reasonable
chance of success without this knowledge. Because
of the lack of evidence for pathotype differences,
resistances identified at one location
are likely to be effective at other locations. A
screening technique that reduces the amount of
labor required would be useful. In this regard, at
Samaru, Nigeria, and Bengou, Niger, simply
bagging heads, without inoculation, generally
gives at least moderate levels of disease pressure
for screening.
Nematodes
Although the more commonly reported genera
of nematodes that attack pearl millet are Melo-
102
idogyne, Pratylenchus, and Tylenchorhnchus, at
least 25 genera of plant parasitic nematodes are
reported to be associated with pearl millet
(Sharma 1985). However, the extent of damage
caused by nematodes in pearl millet is not well
documented. In Senegal studies conducted in
farmers' pearl millet fields demonstrated yield
reduction due to nematodes to be as high as 40%
(J.D. Prot, personal communication). Surveys
and related research are needed to better document
the importance of nematodes in reducing
pearl millet yields.
Striga spp
Striga hermonthica is a very important problem
on pearl millet in Sahelian and sub-Sahelian Africa.
5. asiatica occurs on pearl millet in India and
southern Africa, and to some extent in eastern
Africa, but it is of far less importance than S. hermonthica.
Very little has been reported with respect
to these parasites on pearl millet, although
both attack sorghum and maize on which three
has been considerabe research. Studies in Africa
indicate that there are strains of S. hermonthica
that are more or less specific to pearl millet or
sorghum, and possibly also to maize (Jones 1955;
King and Zummo 1977). Resistance to S. hermonthica
or S. asiatica in pearl millet has not been
confirmed. Although relatively little resistanceidentification
work has been conducted on pearl
millet, it may be that high levels of resistance do
not exist in this crop. Local varieties in western
Africa generally show some tolerance to S. hermonthica.
However, tolerance is not a very useful
strategy for handling the Striga problem, because
tolerant lines support the growth of relatively
large numbers of Striga plants that in turn
produce considerable quantities of Striga seed
that remain in the soil and become troublesome
in succeeding years.
A concerted effort should be made to determine
if resistance to Striga occurs in pearl millet.
However, an improvement in the reliability of
screening techniques may be necessary before
successful resistance identification is achieved.
It is likely that control of Striga in pearl millet
will depend heavily on cultural practices, but
resistance, if found, could play an important role
in an integrated approach to the control of this
important parasite,