Epidemiological studies on bacterial spot of bottle gourd and pumpkin caused by Xanthomonas cucurbitae

Bacterial leaf spot caused by Xanthomonas cucurbitae is a worldwide disease of cucurbits that leads to high crop losses mainly in bottle gourd and pumpkin under the sub-tropical zone of Himachal Pradesh. In plant disease development, temperature and relative humidity are two critical factors. We determine the impact of these variables on the development of the disease in order to know how specific environmental factors affect the bacterial spot of bottle gourd and pumpkin. About one month old seedlings were inoculated with bacterial suspension (1-10 cfu ml ) through pinprick spray inoculation and were firstly placed in the 8 -1 desiccators maintained at different relative humidity levels (80.5, 85.7, 89.9, 95.6 and 100.0%). Afterwards, they were kept in BOD incubators adjusted to different temperature regimes (20, 25, 30 and 35 C) to obtain the combined effect of various temperature and relative humidity regimes on the initiation and development of the disease. The mean incubation period in bottle gourd and pumpkin was maximum at 20 C with 80.50 per cent relative humidity and minimum (23.33 h and 25.33 h) at a combination of 35 C with 100 per cent relative humidity. The temperature range of 30-35 C and relative humidity of more than 80 per cent was favourable for bacterial spot of bottle gourd and pumpkin caused by X. cucurbitae.. KEYWORDS :Bottle gourd, disease severity, epidemiology, pumpkin, Xanthomonas cucurbitae