Epidemiology and spread of potato early blight in West Bengal

Studies were undertaken for two consecutive cropping seasons on prevalence of air horne conidia of Alternaria solani in relation to weather conditions. Counts of conidia trapped on slides on aeroscopes exposed for 12 hours were made twice daily once at 5 p.m. and another at 7 a.m. Daily records of maximum and minimum temperature, maximum and mimmum relative humidity, wind velocity, dew deposition and sunshine hours were kept. Conidia could be detected from the third week of December till end of March with perceptible increase from third week of January to end of February. Highly significant positive correlation was found between maximum and minimum temperature, maximum relative humidity, wind velocity and dew deposition. Partial regression showed maximum temperature to play the major role and wind velocity to some extent.

Study on progress of infection of early blight of potato in the field and individual plant for two consecutive years on cultivar Kufri Chandramukhi was made. In the first year of study, disease appeared early in the first week of Janury and progress was comparatively slow in the initial stages. A typical logarithmic curve of progress of infection could be made out. In the second year, diseases appeared in the third week of January and progress was very rapid and almost linear. Spread was local and limited to surrounding plants Disease in an individual plant was found to be located more on the leaves near the base and intensity gradually decreased on the leaves towards the apical region.