Influence of post-inoculation diurnal conditions on development of Ascochyta blight of peas

causes necrotic spots on all aerial parts of the pea plants including the pods. Disease was more severe on the lower parts of the plant. The pathogen is a necrotic and grows in the apoplast of the host cells (2). The disease developes rapidly under wet weather and moderate temperature due to fast growth of the pathogen and host growth. Precise data of disease during critical periods are lacking under Punjab conditions, therefore, parameters like diurnal variations in temperature and relative humidity were studied to see their effect on incubation period, per cent lesion area and disease severity due to Ascochyta blight. Five to six pea (Pisum sativum L.) seeds of variety Punjab-87 were sown and were thinned to 2 plants per pot. Plants were grown in a temperature controlled growth room at 20±2°C. Pycnidiospore suspensions were obtained by culturing the fungus on PDA (Potato Dextrose Agar) at 20±2°C for 8-10 days, flooding the cultures with distilled water, gently scraping the surface and filtering through cheese cloth to remove the mycelium. For each experiment, ten plants (5 pots) were incubated with 20 ml of the pycnidiospore suspension applied with a spray atomizer. The plants were covered with clear perforated polythene bags immediately after inoculation. One month old plants were inoculated with 1 x 106 pycnidiospores per ml providing 24h wetness period for better disease development. These plants were shifted to glass house and in the field to observe the effect of diurnal temperature conditions on disease development. Each experiment was repeated six times and disease was observed on a 0-5 scale (6) during the month of November-December 2000 an