Etiology and epidemiology of collar rot complex of cowpea.
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Date
2019-09-30
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CSK HPKV,Palampur
Abstract
The present investigation entitled “Etiology and epidemiology of collar rot complex of cowpea” was undertaken to identify the associated pathogen(s), factors affecting the pathogen & disease development and effect of weather variables on the diseases development. Collar rot of cowpea is known to be caused by number of pathogens and is one of the most destructive disease in Himachal Pradesh. Isolation was taken from the diseased samples and three fungal pathogen were isolated among which pathogenecity was established only with Sclerotium sp. On the basis of symptological and morpho-cultural characteristics of test pathogen, the pathogen was ascertained as Sclerotium rolfsii. Maximum mycelial growth and sclerotial production was observed on potato dextrose agar and oat meal agar at 30°C to 25°C, respectively. Incubation and latent period of S. rolfsii was observed to be 7 and 13 days respectively. Inoculum load of pathogen was tested between 1g-5g/kg of soil and 2g/kg of soil was found optimum, which gave 86.66 percent disease incidence. Young and early generation of cultures gave maximum disease incidence of collar rot. Significant decrease in the disease incidence was observed with increase in age and sub-culturing of pathogen. The disease incidence was observed maximum at low soil moisture and disease incidence was decreased with increase in soil moisture. Sandy clay loam soil gave the maximum per cent incidence of disease and minimum was observed with silty clay loam. The disease incidence was observed minimum in early sown crop as compared to normal and late sown crop. The minimum disease incidence was also observed at wider spacing (60 cm), as compared to normal (45 cm) and closer (30 cm) spacings. Maximum disease incidence 76.53 per cent was observed on late sown and narrow spaced crop (30 cm) as compared to timely and normal sowing and wider spacing. Disease incidence was highly positively correlated with temperature (minimum, maximum and average) and relative humidity (minimum, maximum and average) on all the dates and sowing. The coefficient of determination revealed that the temperature and relative humidity contributed 97.8, 90.06 and 97.1 per cent towards incidence of collar rot on crop sown at 7th June, 22nd June and 8th July, respectively. AUDPC and infection rate (r) followed the similar trend of disease incidence with respect to 7th June, 22nd June and 8th July date of sowing.
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