RA 00110.pdf - OAR@ICRISAT

Biology and Epidemiology of Downy Mildew
of Pearl Millet
H. S. Shetty 1
Abstract
Sclerospora graminicola is an important pathogen on pearl millet, prevalent wherever the crop is
cultivated in the semi-arid tropics. The primary inoculum source is seed or soil, but the secondary spread is
by airborne sporangia. Sexually produced oospores can survive under dry conditions for more than 5 years.
Asexual propagules are ephemeral and fragile. Their production, liberation, deposition, and germination
are greatly influenced by environmental factors, as are penetration, infection, and disease development.
Epidemiological studies indicate that dew formation is the most important factor that governs disease
development. In addition, disease incidence positively correlates with relative humidity and maximum
temperature.
S. graminicola is an obligate parasite. Axenic growth (culture in artificial medium) of the fungus has
not been possible thus far. The fungus was cultured in association with its host tissue callus (dual culture)
and the life cycle was completed successfully in vitro. Inoculated seeds and systemically infected shoot tips
of the host are good source materials to establish the dual culture on a semi-synthetic medium. The dual
culture technique can be utilized to screen host cultivars against downy mildew reaction. Vegetative
mycelium of S. graminicola is coenocytic. During sporogenesis nuclei migrate to sporangiophores and
sporangia to form multinucleate structures. Zoospores formed from sporangia are uninucleated. There is no
nuclear division in the zoospores, sporangia, and sporangiophores. However, nuclear divisions are common
in the germ tubes of zoospores during germination.
1. Plant Pathologist, Downy Mildew Research Laboratory, Department of Applied Botany and Seed Pathology, University of Mysore,
Manasagangotri, Mysore, Karnataka 570006, India.
ICRISAT (International Crops Research Institute for the Semi-Arid Tropics). 1987. Proceedings of the International Pearl Millet
Workshop, 7-11 April 1986, ICRISAT Center, India. Patancheru, A.P. 502324, India: ICRISAT.
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