Abstract

16 isolates of Phomopsis azadirachtae, causing die-back of neem were isolated from 16 different geographical regions of Tamil Nadu. Their growth response to physical (temperature and pH) and chemical (carbon and nitrogen sources) factors were investigated. The toxicity of culture filtrate of each isolate on neem seed germination was also studied. Several isolates exhibited maximum growth at 35°C. Maximum growth of all the isolates was observed at pH 6.0. Many isolates preferred starch and a few, sucrose, as carbon sources. Ammonium sulphate formed the good nitrogen source for most of the isolates. However, all the isolates displayed significant differences among themselves in their growth response to each treatment. The culture filtrate of each isolate inhibited the germination of neem seeds but exhibited varying degree of toxicity. The results obtained suggest the existence of physiological variability within P. azadirachtae.

Key words: Die-back of neem, carbon source, culture filtrate, isolates, nitrogen source, pH,Phomopsis azadirachtae, temperature, variation.