Sorghum Diseases in India

hybrids will probably always lag behind those
of other hybrids in a breeding program. Will
farmers accept resistance with lower yield in a
situation where epidemics are generally infrequent?
Seed producers are not likely to be interested
in producing seed of hybrids that may not
sell well or that have a very limited market.
Another question requiring clarification is the
actual seriousness of ergot toxicity. Finding answers
to these questions is critical, because any
program for breeding of ergot-resistant hybrids
or even one for breeding ergot-resistant varieties
is very resource consuming. For areas where ergot
is a likely problem perhaps other methods,
such as pollen management or using existing
resistant lines directly as varieties, should be
considered before additional resources are expended
in breeding for resistance. Breeding for
ergot resistance from scratch is not practical for
a resource-limited program; it would be better to
examine the direct use of already identified resistances
as varieties.
There is some need to determine if genotype
x environment x pathogen interactions affect
quantitative or qualitative differences in the alkaloid
content of ergot sclerotia. Host reaction to
ergot depends considerably on speed of flowering
events, and these are influenced, likely,
considerably by temperature, with cooler temperatures
generally prolonging the protogyny
period.
Smut
Smut was first reported on pearl millet in the
early 1930s in Senegal (Chevalier 1931) and India
(Ajrekar and Likhite 1933). As with downy mildew
and ergot, smut gained greater significance
as a pearl millet disease in India, especially in
northern India, with the adoption of hybrids. In
the Sahelian Zone of western Africa, smut is generally
considered to be more important than ergot.
Tolyposporium penicillariae Bref. seems well
accepted as the name of the causal organism,
although Moesziomyces has been suggested as a
more appropriate genus name (Knower 1977).
Like ergot, infection is believed to be through
stigmas (Nary 1946); however, unlike ergot,
highest levels of smut infection are obtained if
inoculation is done before newer (boot-leaf
stage) rather than at newer (Thakur et al. 1983b).
Infected florets produce sori that are usually
top-shaped and somewhat larger than grain.
They are at first green, but as panicles mature
they turn brown and by harvest rupture relatively
easily.' Sori contain teliospores in aggregates
called 'sporeballs', each consisting of up to
several hundred teliospores (Subba Rao and
Thakur 1983). Soilborne teliospores germinate
and produce windborne sporidia that infect florets.
It is possible that teliospores also become
windborne and germinate to produce sporidia
on the pearl millet plant. Secondary spread of
inoculum may also occur from early-flowering
panicles to late-flowering ones (Vasudeva and
Iyengar 1950).
Tarr (1962) reports having observed sori on
pearl millet that were typically cylindrical and
elongate, resembling sori of long smut of
sorghum. The fungus concerned was morphologically
identical with Tolyposporium ehrenbergii,
the sorghum long smut pathogen.
Teliospores of pearl millet smut have been
observed to germinate only at a low frequency
on artificial media and in water (Bhatt 1946;
Subba Rao and Thakur 1983). The fungus can be
readily cultured on several media, including potato
dextrose agar, potato agar, and carrot agar.
Growth is by budding. Precise information on
environmental conditions associated with natural
infection has not been reported, although it is
generally believed that a warm, humid environment
accompanied by some wind promotes the
disease.
Some fungicides have been found to reduce
smut infection when sprayed onto panicles at
the boot stage or shortly thereafter. However,
this is not considered to be a practical method of
control for pearl millet farmers. Little information
is available on effective control through cultural
practices.
An effective screening technique to identify
smut resistance has been developed (Thakur et
al. 1983b). It involves inoculating panicles with a
sporidial suspension at the boot-leaf stage, covering
the boot with parchment paper bags, and
maintaining high relative humidity with some
sprinkler irrigation on rain-free days.
Many resistant lines have been bred, and
many of these have shown stable resistance to
smut in multilocational testing in India and
western Africa (Thakur et al. 1986). In limited
testing, resistance identified in India is effective
in western Africa (ICRISAT, unpublished). Smut
resistance is more readily available and more
101