PYRICULARIA ORYZAE: RACES DISTRIBUTION AND SCREENING OF FUNGAL ANTAGONISTS IN VITRO

Abstract

One of the suggested blast disease management approaches is integrated disease control, which combines cultivation practices, resistant cultivars, and fungicide applications as appropriate. Planting resistant varieties are the most cost-effective option, but the resistance is quickly broken down over seasons and areas due to the existence of many races. Planting resistant varieties should therefore be accompanied by other control methods like biological control techniques. Selecting varieties with resistant gene(s) that match the pathogen race in the field is recommended. It is therefore critical to monitor the race composition in the area. This study aimed to determine races of Pyricularia oryzae isolated from different subdistricts in Pinrang, Bone, Maros, and Gowa regencies and the potential of rhizosphere fungal isolates to inhibit the growth of three dominant fungal blast races. Pyricularia oryzae was isolated on rice that showed specific symptoms of blast disease. Blast pathogen was grouped into races using 7 rice differential variety sets: Asahan, Cisokan, IR64, Krueng Aceh, Cisadane, Cisanggarung, and Kencana Bali. Observations were carried out 7 days after inoculation based on the standard evaluation system according to IRRI. The antagonists were isolated from the rhizosphere of healthy rice plants, followed by the dual culture test on Potato Dextrose Agar (PDA). A total of 42 isolates were collected from blast-infected rice, and 14 isolates were obtained from the rice rhizosphere. Based on the reactions of 7 differential varieties, a total of 18 races were determined. Races 000 and 001 were dominated with every 6 isolates, followed by races 003 and 020 with 5 isolates each, and races 033 and 013 with 4 and 3 isolates respectively. The other races were found only every two or single isolate. Dual culture using fungal rhizosphere isolates revealed that five isolates had inhibition above 75% against 3 representative races of P. oryzae. Based on the findings, it is suggested that the variation of P. oryzae races in 4 regencies in South Sulawesi is significantly high, and dominated by 2 races. The five rhizosphere fungal isolates may be used as potential bioagents for the eco-friendly management of rice blast disease.