Farhat F. Jamil

Phytoalexin synthesis in the juvenile sorghum leaf

Abstract Infection of the juvenile sorghum leaf by Colletotrichum graminicola (a pathogen) and Helminthosporium maydis (a non-pathogen) resulted in the rapid accumulation of a phytoalexin pigment complex previously identified from the sorghum mesocotyl. The principal pigments have been identified as the 3-deoxyanthocyanidins, apigeninidin and luteolinidin, but the complex includes several as yet unidentified pigment components. After the onset of penetration, components of the complex rapidly accumulated to nanogram levels within a highly restricted area at the infection site. Because of the speed of synthesis, occurrence in response to attempted infection, and previously reported fungitoxicity of the components, we propose that synthesis of the pigment complex constitutes a defense response in the juvenile sorghum leaf. The results show that the preformed cyanogenic glycoside, dhurrin, is not the only source of resistance of sorghum seedlings to fungal infection.

Cultural studies on Colletotrichum graminicola isolates from shattercane, sorghum and corn.

Cultural studies were undertaken on three isolates of Coletotrichum graminicola obtained from anthracnose infected sorghum ( Sorghum vulgare ), shattercane ( Sorghum bicolor ) and corn ( Zea mays ). Radial growth and sporulation of these isolates were compared on 7 culture media. The effect of culture age on germination of the spores was also determined. Oatmeal agar was found to be a good medium for vegetative growth and sporulation. Better sporulation was obtained on media containing sucrose as a carbon source.