Comparative analysis of leaf spot disease in Rice Belt of Punjab, Pakistan

Background: Brown leaf spot (BLS) caused by Bipolaris oryzae (Breda de Haan) Shoemaker, is a chronic disease of rice that infects millions of hectares worldwide each year. In this study, a total of 18 rice growing districts of Punjab, Pakistan were surveyed during cropping season in 2014-17 for the incidence of BLS disease. Methods: The survey method was used to gather the data of BLS incidence during 2014-2017 in 18 districts of rice growing areas of Punjab, Pakistan. Meteorological data was collected from the weather stations of each surveyed district and co-related with BLS incidence. Results: The findings of the study revealed that quantitative relationship exists between meteorological variables and BLS incidence. The incidence of disease in the field was at peak during the month of October. The disease incidence varied from 1.12% to 14.37% over a period of study i.e. from 2014-2017. However, the role of relative humidity (RH) was highly positively correlated with the incidence of disease. Relative humidity showed a positive correlation with the incidence of disease as indicated by the year in which it was towards the high values. The highest disease incidence was observed in district Sargodha whereas the minimum in district Okara. The highest incidence of BLS disease was found in variety Basmati Super (51.43%) and the minimum in Basmati 386 (6.57%). Conclusion: Our study revealed that the fluctuations in temperature did not depict an appreciable impact on the incidence of BLS as indicated by the statistical coefficient, whereas RH strongly influenced the incidence of BLS incidence