ASSESSMENT OF MOSTLY CULTIVATED BORO RICE VARIETIES AGAINST RICE BLAST CAUSED BY MAGNAPORTHE ORYZAE AND ESTABLISHMENT OF KOCH’S POSTULATE THROUGH PATHOGENESIS

Abstract

In Bangladesh last few years, Rice blast caused by fungus, Magnaporthe oryzae played vital role in reducing the yield. In the current study, a field, lab and cup tray experiment was carried out in the Department of Plant Pathology, Sher-e-Bangla Agricultural University (SAU), Dhaka-1207 during the period October, 2018 to May, 2019. The field experiment was conducted in central farm of SAU for the evaluation of the mostly cultivated boro rice varieties viz. BRRI dhan 28, BRRI dhan 29, BRRI dhan 58, BINA dhan 8 and BINA dhan 10, two high yielding varieties viz. BRRI dhan 74 and BRRI dhan 81 and one wild variety against rice blast pathogen. The lab experiment was done in Molecular Biology and Plant Virology Lab for the etiology study of rice blast pathogen. Potato sucrose agar (PSA) media was used to isolate the blast pathogen and identification was done on the basis of cultural and morphological structures of Magnaporthe oryzae. A cup tray experiment was also carried out to establish the Koch’s postulate through pathogenicity test. From the field experiment, it was found that the disease incidence and severity of rice blast was showed significant variants among the tested varieties and ranged from 0.00 to 21.48 and 0.00 to 60.48% respectively. The highest disease incidence and severity was recorded in BRRI dhan 58. There was no disease incidence (0.00%) and severity (0.00%) was found in selected wild variety throughout the growing season. Other varieties showed moderate disease incidence and severity that was statistically not significant each and other. From the study, it was noted that the disease severity of rice blast in tested varieties was showed moderately resistant to susceptible and the selected wild variety showed tolerance/highly resistance to blast pathogen. From the cultural and morphological study of the derived isolate from the field samples, it was evident that the disease was caused by Magnaporthe oryzae, as the isolate produced hyaline, pyriform three celled conidia from leaf sample and media respectively. The etiology of rice blast pathogen was also studied through establishment of the Koch’s postulate. In the study, yield and yield contributing characters of selected boro rice varieties against blast disease was also studied, and it showed statistically non-significant. However from the study it may be concluded that wild cultivar can be alternative of BRRI dhan 28 and BRRI dhan 58, but it needs further more trial. This wild variety can also be used in resistance breeding program to develop the induced resistance system in rice plant.