Sorghum Diseases in India

soil erosion is seldom controlled. The net result
of these practices adds up to a very low yield
average (1.5 t ha -1 ) for Central America and the
Caribbean.
In most countries of the Central American
region, there are current efforts underway to
increase sorghum yields. Improved cultivars,
mostly photoperiod-insensitive and early-maturing,
are available and recommended for cropping
under high-input systems. The farmer
must rely on the availability of credit and technical
help from extension agencies. Improved cultivars
do not function well in association with
maize.
In El Salvador and the Honduras, crop improvement
efforts also include the development
of higher-yielding, photoperiod-sensitive sorghums
that can be used in association with
maize. The practice of sowing maize with sorghum
is a risk-reducing strategy, especially in
areas where the maize may fail due to lack of
rains at critical growth stages. The sorghum crop
(maicillos) is more drought-resistant, but maize
(maize, or maize grueso) is the preferred crop.
Maize-sorghum intercropping, advantageous
as it is in these areas, can sometimes result in
more disease problems. Maize dwarf mosaic affects
maize and sorghum, and its incidence can
be higher in maize-sorghum fields than in sorghum
growing alone (Wall 1986).
Most of the diseases of sorghum are present
in Central America. Notable exceptions are
witchweed, long smut, and ergot.
Important Diseases
There are variations in the relative importance of
particular sorghum diseases from one area to
another, and from one season to the next. But
certain diseases, such as gray leaf spot, are widespread
and endemic; others are particularly important
in one area. Some diseases may become
important only in a particular year.
Sorghum diseases were surveyed in the Honduras
between 1983 and 1985. A disease inventory
was compiled, and the relative importance
of these diseases was estimated from their incidence
and severity. Finally, yield losses due to
the most important diseases were estimated
(Meckenstock and Wall 1987).
These studies show that, overall, the most important
diseases on the basis of incidence times
68
severity were gray leaf spot, oval leaf spot, rust,
ladder leaf spot, and zonate leaf spot, respectively.
On a regional basis, their importance varied.
Sorghum downy mildew, for instance, was
totally absent in Choluteca (southern the Honduras),
although it was the most important disease
in the Comayaguan area of the country.
Certain diseases, important at the beginning of
the season, were insignificant at the time of
harvest; such was the case with anthracnose. Improved
cultivars (photoperiod-insensitive),
which are not intercropped and are usually fertilized,
had stalk rot problems, while this disease
was hardly seen on intercropped, photoperiodsensitive
sorghum (maicillos). The fact that the
latter are normally not fertilized may indicate
that the stalk rot problem is induced; if so, it
would be expected to become more important
with increased use of fertilizers and improved
sorghum cultivars.
Foliar diseases
The most prevalent foliar disease in Guatemala,
the Honduras, and El Salvador, and perhaps in
all the other countries of the region, is gray leaf
spot (Cercospora sorghi Ellis and Everhart)
(Escobedo et al. 1979; Meckenstock and Wall
1987; Wall 1980). It can be found anywhere sorghum
is grown, and affects perennial weeds,
such as Sorghum halepense, that no doubt play an
important role in maintaining the inoculum of C.
sorghi and many other pathogens throughout the
year. Gray leaf spot affects sorghum plants early
in their development; on intercropped susceptible
varieties, young plants can be severely defoliated
while still in the shade of the maize crop
(Wall 1980). The fungus infects leaves and stems,
with yield losses up to 15% (Meckenstock and
Wall 1987).
Rust (Puccinia purpurea) is also found everywhere,
particularly towards the end of the rainy
season, becoming more severe with the onset of
the dry season. It is an important disease of sorghum
in Panama (Jimenez 1984). This disease
can cause defoliation on susceptible varieties. A
hyperparasitic fungus, Darluca filum, occurs on
rust of sorghum (Contreras and Barahona 1974),
attacking also maize rust (P. sorghi). Certain dipterous
larvae also feed on the pustules formed
by the rust fungus. Like Cercospora sorghi, P. purpurea
also infects johnsongrass.