Sorghum Diseases in India

Cultivar CS 3541 is not.resistant to SDM in
Comayagua. This cultivar is the genetic base for
most, if not all, improved varieties and hybrids
produced to date by the Honduran sorghum
project. This is risky, because crop-threatening
SDM epidemics could occur due to the lack of
resistance in the improved cultivars. To prevent
this situation, it is important that more genetic
diversity be used in the formation of future releases
in the country.
Disease Severities Under Different
Cropping Systems
Many cropping systems are used by sorghum
producers in the Honduras. It is not uncommon
to find several species intercropped in small
fields, because this permits more efficient use of
land, labor, and other resources. Land resources
are scarce for subsistence farmers in the Honduras.
Microclimate is thought to be an important
factor in host-parasite interactions, and in epidemic
development (Wiese 1980). The cropping
systems practiced by subsistence farmers in producing
sorghum in the Honduras may have important
microclimatic and various other differences
associated with them. These could have
viable effects on plant health in the course of one
cropping season, particularly in the case of polycyclic
diseases.
Several cropping systems involving sorghum
are found in other American tropical areas (Rao
1985; SRRNN 1984). The most widely practiced
sorghum cropping system in Central America is
that of sorghum-maize intercropping. This is the
most popular cropping system in both El Salvador
and the Honduras, accounting for more
than 90% of the sorghum production in these
two countries. Other systems include sorghum
sown alone or intercropped with maize and
beans, beans, cowpeas, 'ayote' (Cucurbita sp),
sesame, and cassava.
Sorghum-maize intercropping is popular as a
risk-reducing system where there is danger of
droughts. From a standpoint of human nutrition,
sorghum-bean is a desirable farming system,
as noted by De Wait and De Walt (1984).
McCulloch and Futrell (1983), in a socioeconomic
and nutritional study in southern
Honduras, concluded that the most nutritionally
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efficient cropping systems were those with the
highest yields of sorghum and beans. In both of
these studies, the term 'beans' is used to mean
any of several Phaseolus and Vigna species. Beans
are an important part of the diet in the Honduras
and in southern Honduras; so is sorghum.
However, national production has been insufficient
to meet demand for either commodity, and
importation has become necessary (SRRNN
1984). Seeing this need, in addition to sorghummaize
and sole sorghum, the sorghum-bean
cropping system was also studied with respect
to disease development.
Results and discussion
Sorghum-bean intercropping showed no increase
in incidence of sorghum disease. Landraces
yielded more than improved cultivars in
this system. This was not the case in sole sorghum
plots in other studies (Fig. 3). The advantage
of the improved cultivars is manifested at
higher plant densities. Landrace cultivars or
maicillos are better adapted at lower plant densities
because they tiller profusely; when intercropping,
plant density for any of the component
species is less, so it is not surprising that
landraces adapt better to such systems. Plant
height may also contribute, as the taller maicillos
suffer no competition for light from the beans.
Oval leaf spot was more severe in sorghum
alone than in the sorghum-maize system. This
was not the case for gray leaf spot. One difference
may lie in the dispersal mechanisms. Gray
leaf spot is more widespread than oval leaf spot
although, where it occurs, the latter can be more
severe. This may be due to a more pronounced
influence of inoculum originating outside of the
field in question for gray leaf spot, and a larger
dependence of inoculum originating within the
field for oval spot. Sorghum-maize intercrop
ping imposes greater distances between sorghum
plants and fewer sorghum plants per unit
area.
Improved cultivars appeared to have fewer
foliar diseases, but not lower severities, than
maicillos when sown in postrera (second sowing
season) under subsistance farmers' conditions,
i.e., with little or no fertilization. Yield levels of
the farmers' sowings, however, were quite low;
panicle size was very small. With sufficient fertilizer,
improved cvs sown at higher densities