Correlation between weather variables and ascochyta blight disease of chickpea

Abstract

Relationship of weather variables and chickpea ascochyta blight disease was studied using 24 years (1985-2008) data collected at Ludhiana, Punjab. Coefficients of correlation of ascochyta blight disease index (DI) were worked out with meteorological variables at weekly intervals starting from 5th SMW (standard meteorological weeks) to 17th SMW and utilized to develop regression model in disease forecasting. Minimum temperature (Tmin), morning relative humidity (RHmax), rainy days exhibited positive correlation with DI, however, (maximum temperature (Tmax) and the sunshine hours showed negative correlation. The relationship between DI and Tmin appeared to be exponential; DI sunshine hrs; DI rainfall appeared to be polynomial and regression lines explained 26%, 49% and 22% variation in disease respectively. The relationship between DI and afternoon relative humidity (RHmin); DI and humidity thermal ratio (HTR) appeared to be power function and regression line explained 34% and 35% variation in disease respectively. The favourable range of Tmin and weekly mean RHmin values were 12.5-14.5oC and 45-60%, these two variables were combined as HTR, the values of which ranged from 0.4-0.5 for disease occurrence in central plain region of Punjab. The study concluded for maximum probability of disease from 7th-10th SMW which is also the beginning of reproductive phase of chickpea.

Keywords

• Chickpea
• Ascochyta blight
• weather variables
• disease index