EPIDEMIOLOGY OF RICE BLAST (PYRICULARIA ORYZAE) DISEASE IN CENTRAL PUNJAB, PAKISTAN

Rice blast disease (RBD) is mostly controlled by fungicides by the farmers of central Punjab, Pakistan. However, the use of fungicides by the farmers is excessive and ill-advised, resulting in the emergence of new resistant strains of Pyricularia oryzae. The ill-advised employment of fungicides can be timed exploring the role of environmental factors favorable for this disease. The objective of current study was to determine the most favorable weather conditions for RBD in central Punjab, Pakistan, where this crop is mostly cultivated. Environmental factors including maximum and minimum temperatures (max and min temp), rainfall (Rf), relative humidity (Rh) and wind speed (Ws) conducive for RBD were characterized during this study. For this purpose, eight years (2009-2016) RBD severity data of susceptible to highly susceptible genotypes together with environmental data (max and min temp, Rf, Rh and Ws) was collected from Kala Shah Kako (KSK), Rice Research Institute (RRI), Punjab, Pakistan. The genotypes were cultivated for eight years in randomized complete block design (RCBD), and data was kept on recording during the months of high disease pressure. Data was collected after a ten days interval using disease scoring scale developed by International Rice Research Institute (IRRI) during 1996. Simple linear regression models were used to determine the relationship of environmental factors with RBD severity. The variation in RBD severity due to environmental factors was determined using the coefficient of determination (R²). In the present study, the relationship of max temp, Rf, Rh and Ws with RBD severity was positive, significant and linear, however, the relationship of min temp with RBD severity was negative. Max temp 40-42°C, min temp 21-23°C, Rf 2-3mm, Rh 50-70% and Ws 9-11 Km/h were found to be most favorable environmental conditions for RBD severity. The current research disclosed the significant role of all five environmental factors in the spread of RBD. Thus, future predictive models could be established using these five environmental factors for more accurate prediction of this disease in rice belt of Punjab, Pakistan, to time the application of fungicides.