PHENYLALANINE AMMONIA-LYASE ACTIVITY IN PEARL-MILLET SEEDLINGS AND ITS RELATION TO DOWNY MILDEW DISEASE RESISTANCE

Phenylalanine ammonia lyase (PAL) activity was studied in different ge notypes of pearl millet with varying degrees of susceptibility to down y mildew disease, after inoculating with Pathotype 1 of Sclerospora gr aminicola. In resistant genotypes, the enzyme activity significantly i ncreased 24 h after fungal inoculation while in the susceptible genoty pes, the activity decreased. The increase or decrease in enzyme activi ty was well-correlated with the degree of host resistance to the patho gen. A time-course of change in activity of PAL after inoculation show ed a considerable difference between resistant and susceptible genotyp es. Studies on the activity of PAL in different parts of pearl millet seedlings revealed that in the resistant genotype, enzyme activity sig nificantly increased at 24 h post-inoculation only in the shoot portio n, whereas in mesocotyl and root the activity decreased. In susceptibl e seedlings, enzyme activity decreased at 24 h post-inoculation in sho ot, mesocotyl and root. The activity of PAL was also found to be patho type-specific. Histochemical tests for lignin were positive in infecte d cells in the resistant genotypes. The role of PAL in imparting resis tance to pearl millet against downy mildew disease is discussed.