Enhancement of downy mildew of sorghum by some organic soil amendments: a caution to organic farmers.

Matured botanical compost ofCroton sparsiflorusandAzadirachta indicawere evaluated for promotion of sorghum downy mildew at the rate of 0.5% (w/w). Exceptionally high promotional rates of 26.9% (C. sparsiflorus)and 30.1% (A. indica)were observed as compared to negative control (8.8%). The enhancement of disease was higher than that obtained by the supply of recommended dose of urea (13.3%). As the pathogen (Peronosclerospora sorghi) is a biotroph and cannot multiply by using organics as nutrient source in the absence of a host, the mechanism of disease enhancement is inferred to be through stimulation of oospore germination by organic compounds. [ABSTRACT FROM PUBLISHER]