RA 00110.pdf - OAR@ICRISAT

The effects of different factors, i.e., temperature, relative humidity, spore drying, spore washing, p H , and
light on germination of urediniospores and teliospores were studied. The duration of incubation period
influenced the percentage spore germination.
The Pertinence of Gynoecial Structure and Pollination Dynamics to Ovary Infection of
Pearl Millet by Ergot
(Importance de la structure du gynecee et de la dynamique de pollinisation dans l'infection
des ovaires de mil par l'ergot)
J. Willingale
Biochemist, Imperial College of Science and Technology, London SW7 2AZ, UK
Ergot of millet is a floral disease in which the pathogen invades the host ovary and replaces plant tissue with a
mass of sphacelial hyphae. Fungal growth is supported by the endogenous gynoecial nutrient supply which
under normal circumstances would support ovule fertilization and subsequent grain development.
Successful establishment of the fungus depends on compatible entry into the ovary tissue without causing a
hypersensitive reaction by the host. The path of entry traced by invading hyphae is dictated by pistil
morphology. Penetration appears to be controlled by physiological and biochemical parameters associated
with pollination and fertilization. Hyphae penetrate and travel down the stylodia, closely following the path
taken by millet pollen thus providing direct entry into the upper ovary wall.
As host tissue is replaced, hyphae can no longer obtain sufficient nutrients for sphacelial growth from
adjacent islands of degenerating host cells, isolated from the main vascular supply. The fungus establishes a
host-parasite interface at the base of the ovary in close proximity to the main ovarian vascular trace, thus
allowing unrestricted nutrient flow into the fungal sink.
Damage to the stigmatic hairs, occupation of the pollen transmission tracts, and stylodial constriction
insure that the pathogen successfully isolates itself from pollen. It is evident that the phenomenon of stigma
constriction provides a basis for ergot resistance in selected lines of pearl millet.
It is known that fertilization imparts resistance in other ergot/host interactions, however elicitation of
stigma constriction in pearl millet, either by compatible host pollen or by ergot hyphae, appears to be a unique
phenomenon. Investigation of pollen and hyphal transmission down the stylodia of pearl millet provides a
novel model to investigate stigma interactions in Gramineae.
Screening Pearl Millet for Resistance to Striga hermonthica in West Africa
(Criblage du mil pour la resistance a Striga hermonthica en Afrique de l'Ouest)
K.V. Ramaiah
Cereals Breeder-Striga, I C R I S A T - U N D P Cooperative Program, B.P. 4881, Ouagadougou, Burkina Faso
and
J. Werder
Principal Millet Pathologist, ICRISAT Sahelian Center, B.P. 12404, Niamey, Niger
The importance of the root parasite Striga hermonthica as a major constraint to pearl millet production in
West Africa and the need for the breeding of host-plant resistance are discussed. Preliminary re-sults of
screening pearl millet for resistance in West Africa are included. Screening in pots led to the identification of
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