Sorghum Diseases in India

physiological maturity of the host and susceptibility
to rust. A reliable method to preserve
urediniospores for at least several months
would facilitate the development and implementation
of more reliable field, and possibly
greenhouse, identification of resistance. Almost
all disease rating scales now being used for
pearl millet rust are based on percentage leaf
area affected. Rating systems that assess pustule
type would also be useful. Evaluation of existing
breeding materials for reaction to rust is advisable
before launching into new, major programs
to identify rust resistance in accessions of germplasm.
With the development of more precise
screening techniques, studies should be undertaken
on the inheritance of resistances other
than those based on a hypersensitive reaction.
Virus and Virus-like Diseases
Virus-like symptoms on pearl millet have been
reported from western Africa, southern Africa,
the Indian subcontinent, and the USA. Symptoms
are of two types, streak and mosaic. Streak
at up to 80% frequency was noted in some pearl
millet lines at New Delhi, India, in the 1970 offseason
(Seth et al. 1972a). This disease was solely
vector-transmitted (Cicadulina mbila) and designated
as the Pennisetum strain of maize streak
virus. A similar disease characterized by intermittent
streaking, dwarfing, and sometimes excessive
tillering was observed in 50% of the
plants (estimated 30% yield loss) in a pearl millet
seed multiplication field in southern India
during the 1986 dry season (S.B. King, unpublished).
Similar symptoms have been observed
(S.B. King) in isolated pearl millet plants
at Patancheru, India, and in Mali, Nigeria, Niger,
and Zambia.
Mosaic symptoms associated with dwarfing
have been reported on pearl millet in northern
and southern C6te d'lvoire (Kukla et al. 1984).
The disease was called pearl millet mosaic;
based on host range, physiochemical properties,
and serology, it was closely related to the mechanically
transmissible, aphid-borne guinea
grass mosaic virus. Seth et al. (1972b) reported a
mosaic on pearl millet that was readily transmitted
mechanically and by Rhopalosiphum maidis.
The virus infected several other grass hosts. In
the USA, Jensen et al. (1983) greenhouse-tested
pearl millet genotypes for reaction to maize
dwarf mosaic virus strains A and B. Many pearl
millet lines were infected to at least a low frequency
by one or both strains. I have observed
mosaic incidence exceeding 80% in a late-sown
isolation of pearl millet near Lusaka, Zambia.
The whole area of virus and virus-like disease
in pearl millet requires sorting out. At
present these diseases appear not to be very important,
but our present lack of knowledge
places production of pearl millet in a rather vulnerable
position. Initially, research is needed on
virus identification and characterization, host
range, transmission, and potential damage to affected
plants. This should be followed by resistance
identification, and then perhaps breeding
for resistance.
Ergot
Ergot was first reported on pearl millet in the
early 1940s in India (Thomas et al. 1945). There
were epidemics in the late 1950s in the area now
known as Maharashtra state (Bhide and Hegde
1957; Shinde and Bhide 1958). However, ergot
did not draw serious attention in India until
after the release of the first hybrid in the mid-
1960s. Subsequent epidemics occurred, primarily
in the early 1970s (Thakur 1984). Epidemics
have not been reported in Africa. Ergot causes
losses in grain yield, because infected florets do
not produce grain. It reduces grain quality, because
ergot sclerotia contain several alkaloids
and contaminate grain. The alkaloids are generally
of the agroclavine group, and are toxic to
man and livestock.
The extent of pearl millet ergot toxicity in
man is not clearly understood. Symptoms include
nausea, vomiting, giddiness, and somnolence
(Krishnamachari and Bhat 1976; Bhat et
al. 1976). Although death of humans has been
reported in India, mainly in the popular press,
there seems to be some question whether sclerotial
ingestion at an expected level would in fact
cause death.
The ergot pathogen on pearl millet was generally
recognized as Claviceps microcephala, until
Loveless (1967) named it C. fusiformis, based on
assessment of specimens in Africa. C. fusiformis
was confirmed in India (Siddiqui and Khan
1973a) and is now the accepted nomenclature.
Many aspects of the disease cycle are well
understood (Thakur 1984;. Thakur et al. 1984).
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