Sorghum Diseases in India

population densities for optimum yields, disease
and yield levels could be simultaneously
studied with density traits on all cultivars.
There is a high degree of heterogeneity for a
number of traits in maicillos. This gives maicillos
the stability that allows production of some
grain, even under quite unfavorable conditions.
With respect to disease reaction, heterogeneity
in a population can slow down epidemic development
(Robinson 1975). As changes are made
in maicillos through breeding programs, sufficient
heterogeneity should be maintained. The
more susceptible genotypes can be eliminated,
replacing them with new sources of resistance.
The resulting plant population would then have
the original sources of resistance (if any), plus
the new ones, and fewer or no extremely susceptible
types.
The intercropping of sorghum with maize
seems to reduce the severity of certain foliar diseases;
however, MDM had higher incidence under
maize-sorghum intercropping than under
sorghum monoculture (Table 7). Cultivars of either
species intended for use in intercropping
should have a high degree of resistance to
MDM. Sources of inoculum, vectors, and the
disease cycle should be studied to develop effective
control strategies.
Sorghum-bean intercropping has been studied
and recommended, based on socioeconomic
and human nutrition considerations (De Walt
and De Wait 1984; McCulloch and Futreil 1983).
There are no known phytopathological reasons
why sorghum-bean intercropping should not be
encouraged. With nutritional, social, and cropprotection
recommendations in agreement, it
should prove an exciting system to promote.
Central Americans have practiced intercropping
for many years (Moreno 1985), so adoption
should not be a problem.
Improved cultivars had fewer disease problems
than maicillos when sown in postrera, the
last season. In other experiments in this study,
maicillos had lower disease severities than improved
cultivars (Fig. 3). Improved cultivars
showed no AW or leaf spot incidence; landrace
cultivars did. In the case of AW, it is likely that
among the improved cvs sown, AW resistance is
the rule rather than the exception. Apparently,
Iandrace cultivars have lower levels of resistance
to this disease; though it is clear that they
can be improved and AW incidence could be
reduced through genetic resistance, much like in
the improved cultivars.
In the experimental plots mentioned above,
plant densities were higher than in farmers'
fields surveyed, and fertilizer application was
almost certainly higher as well. Those farmers
who adopt the improved varieties in place of the
landraces they now use will have to sow at
Table 7. Mean severity of oval and gray leaf spot diseases and incidence (%) of MDMV on sole
sorghum and on sorghum/maize intercrop at Sta. Irene and Sn. Francisco, the Honduras, 1984, and
mean severity of zonate leaf spot at Sta. Irene, the Honduras, 1984.
Mean severity
Sorghum/
maize Sole
Sorghum/ intercrop Standard sorghum Standard
Location variety Disease (%) deviation (%) deviation
Santa Irene,
Choluteca Peloton Oval 15.6 6.18 29.7 7.12
Gray 5.0 3.88 5.0 2.48
MDMV 1
7.6 7.61 1.7 0.82
Sn. Francisco
Zonate 2.0 2.28 5.5 6.44
1984 Gigante Oval 10.0 7.22 15.1 7.77
Gray 6.8 4.06 7.1 1.88
MDMV 1
25.0 8.86 5.0 7.07
1. Incidence (%).
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