Department of Plant Pathology, Punjab Agricultural University, Ludhiana-141004
National Symposium on “Plant Pathology in the Changing Global Scenario” held at National Bureau of Plant Genetic Resources, New Delhi on February 27–28, 2009
Anthracnose of guava caused by Colletotrichum gloeosporioides is one of major constraints in successful cultivation of guava. The disease produces brown to dark spots on the fruits affecting their quality. The weather variables such as temperature, relative humidity, rainfall and number of rainy days greatly influence the development of disease. In order to ascertain the impact of weather parameters on disease development, observations on disease severity were recorded during 2004 and 2005 in the orchard. Efforts were made to develop correlation coefficient between disease severity and weather parameters. It was observed that disease initiated in the field during the second week of July and per cent disease index reached maximum in September. The mean maximum and minimum atmospheric temperature were negatively correlated with the disease development during the critical period (from 1st July to 9th October) having r values of -0.762 and -0.827, respectively during 2004 but in the year 2005, the correlation was positive (0.258) with the mean maximum temperature, however, the mean minimum temperature exhibited a negative correlation (r=-0.621). A significant correlation between disease severity and relative humidity was also recorded during both the years of observations. Per cent disease index also exhibited a positive correlation between rainfall as well as number of rainy days during 2004. Regression analysis of disease index as an independent variable with weather parameters were analyzed by using Microsoft Excel. These parameters follow a linear equation of:
PDI(2004) = -29.1+0.18Tmax-0.13Tmin+0.315Rhmax+0.044Rhmin-0.010Rain-0.221Rainy days—1
PDI(2005) = -51.9+1.71Tmax-1.30Tmin+0.211Rhmax+0.186Rhmin-0.003Rain-0.084 Rainy days—2
The R2 value (coefficient of determination) for the year 2004 and 2005 indicated 98.9 per cent and 83.1 per cent variation, respectively in anthracnose of guava, monitored by providing temperature, relative humidity, rainfall and number of rainy day.
