Effect of climatic variability and weather factors on development of tomato early blight in a hot semi-arid region of Southern India

Effect of cultivars, planting periods, weather and climatic variability on early blight (EB) severity was studied over six kharif seasons (2011–16) at Rajendranagar, Telangana. Wider seasonal variations in onset (July-September) and peak severity (September-November) of EB was noted coinciding with 1–7 and 9–14 weeks after transplanting, respectively. Mean EB severity was highest in 2012 on both calendar (47.8%) and crop age (64%) basis. EB severity on cultivars viz., US 3140 (20.8%) and Lakshmi (21.8%) was significantly lower over Heemsohna (24.2%) and DS 810 (25.8%). Plantings of June-July had higher severity (27.9%) over August-September (19.1%). Maximum and minimum temperature besides rainfall variability over long term normals for 2011–16 was 0.7°C, 0.8°C and 3.6 mm/week, respectively with their corresponding actuals of 31.8°C, 22.5°C and 28.3 mm/week. Negative impact of increasing minimum and maximum temperature and positive effect of increasing rainfall on EB severity was documented. Significant associations of EB severity with weather and climatic variability similar over seasons indicated evolving adaptations of early blight to climate change.