Sorghum Diseases in India

Ergot Disease of Pearl Millet: Toxicological Significance
and a Mechanism for Disease Escape
P.G. Mantle 1
Abstract
Ergot disease of pearl millet, caused by Claviceps fusiformis, not only causes crop losses but
potentially adds a toxic component. Extensive reproductive failure in pigs fed ergotised millet in
southern Rhodesia in the 1950s was manifest, in the absence of any other symptom, as agalactia.
This was subsequently shown in the mouse to be due to the central stimulatory action of the
principal ergot alkaloids agroclavine and elymoclavine. The peripheral pharmacology of the classical
C purpurea alkaloids that cause gangmtous ergotism is absent in the C fusiformis alkaloids,
rendering the millet ergot sclerotia a less toxic hazard to man and farm animals than might be
assumed.
Millet disease is exacerbated by pronounced protogyny that is common in some commercial
hybrids. Ergot-resistant pearl millets selected at ICRISAT Center have very short protogyny and
escape infection as rapid pollination quickly precludes the pathogen's entry via the stigma by the
constriction of a region of the fused stylodia. Control of ergot disease in pearl millet can thus be
achieved directly by efficient pollen management exploiting postpollination stigmatic constriction.
Introduction
Ergot disease is one of the two ovary diseases of
pearl millet, the other being the smut caused by
Tolyposporium penicillariae. Ergot is prevalent in
parts of western and eastern Africa and in India.
It became particularly recognized in both continents
during the 1950s as a significant cause of
reduced grain yield. The loss of photosynthate
in the release of honeydew and associated encouragement
of grain molds are factors which
compound the simple loss of potential grain by
ergot pathogen substitution. It is reasonable to
suppose that the disease is much more ancient,
in keeping with the crop plant itself. It is not
clear whether the fungus arose separately in the
two continents or has spread from a single
source as pearl millet has been grown more
widely in the semi-arid tropics. Ergot became
even more significant as a disease with the intro­
duction of high-yielding hybrid millets in India
in the 1960s (Thakur and Chahal 1987).
In spite of some initial controversy, it appears
that the fungi-causing ergot disease of pearl millet
can be classified within the description of
Claviceps fusiformis made by Loveless (1967). The
only important omission in Loveless' description
concerns recognition of two types of asexual
conidia, which occur usually as a mixture of
the fusiform macrospores and the much smaller
spherical microspores.
Toxicology
1. Professor, Biochemistry Department, Imperial College, London, SW7 2AY, UK.
Interest in defining this plant pathogen was also
stimulated in southern Rhodesia concomitantly
in the 1950s following several extensive outbreaks
of agalactia in sows fed rations containing
ergotized millet (Shone et al. 1959).
Mantle, P.G. 1992. Ergot disease of pearl millet: toxicological significance and a mechanism for disease escape. Pages 129-132 in
Sorghum and millets diseases: a second world review, (de Milliano, W.A.J., Frederiksen, R.A., and Bengston, G.D., eds). Patancheru,
A.P. 502 324, India: International Crops Research Institute for the Semi-Arid Tropics.
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