Sorghum Diseases in India

out-yield landraces, but they suffer higher disease
severities. Two questions arise: what happens
to improved cultivars if sown in the early
season, so as to obtain two crops in a single
year? The problem then is grain molds, rather
than foliar diseases; improved cultivars, almost
totally insensitive to photoperiod, are sown in
May or June and flower in July or August, normally
the period of heaviest rainfall. The second
question: what happens after several years of
sowing improved cultivars in a field? Less biomass,
but more inoculum is returned to the soil.
Will this combination of factors result in
higher disease severities? This needs study. It is
clear that the improved cultivars now in use are
subject to greater disease severities than are the
maicillos. If the former are to replace the latter,
their levels of disease resistance need to be improved
to prevent serious yield losses. Research
is also needed to explore cultural practices that
may reduce disease problems.
Conclusions and Recommendations
In the course of this study, 21 diseases were
identified on sorghum growing in different
areas of the Honduras during surveys from 1983
to 1985. Disease importance varied from region
to region. Cultivars intended mainly for use in
one of these regions need to be resistant only to
diseases important in that region. Those intended
for use in all of the sorghum-producing
regions should possess adequate levels of resistance
to the five diseases found to be important
at all locations in the Honduras: MDM, gray leaf
spot, rust, SDM, and AW. Although SDM was
not found in Choluteca, it has spread to new
areas since the studies began. SDM reduces
yields drastically, and occurs on maize as well as
sorghum.
Survey data were used in deciding upon the
priority diseases for yield-loss studies. These
were carried out for: AW, MDM, gray leaf spot,
oval leaf spot, rust, covered kernel smut, SDM,
and zonate leaf spot. All, except for covered
smut, were found to reduce yields on sorghum.
Experiments on AW and MDM permitted an
evaluation of the effect of these diseases on various
yield components. Acremonium-infected
maicillo plants yielded 33% less than healthy
ones. The more susceptible BTx 623 had a 36%
reduction in yield due to AW. MDM was found
to reduce yields by 52% on maicillos. It is still
necessary to study how different incidence
levels of each of these two diseases may affect
yield levels in a sorghum field.
Results from the SDM studies confirmed the
devastating nature of this disease. The highest
incidence, 42.9%, reduced yield by 43.3%. Results
of this study also show that disease resistance
is not necessarily obtained at a cost in
yield potential, as generally believed; yields in
the resistant and susceptible populations did not
differ at Choluteca, where no SDM occurred.
Yield loss studies with foliar diseases showed
that yields in farmers' fields are reduced by as
much as 15%.
Gray leaf spot severity was negatively correlated
with plant height and panicle length in
farmers' fields; the interaction of these three
variables produced a 14.6% reduction in yield.
The partial effect of gray leaf spot severity was a
7% yield reduction. This suggests that the disease
affected yield by reducing plant height and
panicle length, and that it had a separate effect,
in addition to these, as well.
In the survey conducted during 1985, the
overall severity mean for gray leaf spot was 17%.
This degree of disease severity on cultivar Tortillero
reduces yields by 13.3%. The overall mean
for SDM incidence (%) in the same survey produces
a 11% reduction in yield. In areas where
both diseases occur, this implies that yield losses
may well be more than 20%, although precise
yield-loss estimates in such a case would require
a simultaneous study of the two diseases.
Zonate leaf spot was an important disease in
Choluteca. Not only were its severity and prevalence
among the highest for that region, but it
was also shown to reduce yields by almost 14%
on improved and on landrace cultivars.
There is no doubt that sorghum production
requires effective disease-control strategies. Several
questions arose in the course of these
studies, which if addressed, could lead to the
development of practical means of control. The
roles of plant height, as well as those of related
traits, in disease development need to be clarified.
Plant height and disease severity were correlated
in several of the studies. Selection of the
right combination of morphological traits in a
cultivar could help keep disease levels low.
Plant density and its effect on disease development
likewise needs further study. Since it is
likely that different cultivars require different
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