Effect of nitrogen on development of alternaria blight caused by Alternaria solani of tomato (Lycopersicon esculentum) in rainy and winter seasons

Effect of nitrogen application in relations to concomitant weather factors was studied on the severity of the early blight [Alternaria solani (Ell. & Martin Jones & Grout)] disease of tomato (Lycopersicon esculentum Mill. nom. Cons) in a field experiment for 8 growing seasons. The weather factors recorded 10 days preceding the disease observations showed augmentation in the severity at almost all dosage of N applied (0-250 kg N/ha at 11 levels at an increment of 25 kg/ha). Temperature (maximum and minimum) and the total precipitation increased the disease severity most significantly both in the rainy and winter seasons. Mean maximum temperature of 29.65 degrees C, minimum of 22.09 degrees C and the percipitation of 128 mm in the rainy season and those of 23.40 degrees C, 8.69 degrees C and 7.16 mm, respectively in the winter season favoured the disease-development. Higher relative humidity and the frequency of rain indirectly favoured, the disease-development. The direct role of N levels in increasing the severity was not found significant. A dose of 150 kg N/ha in the rainy season and 175 kg N/ha in winter season was worked out to be optimum for the Alfisol of Chhotanagpur plateau of Bihar.