Pathogenicity of Pyricularia oryzae on elite rice cultivars and geographical distribution of avirulence genes causing blast disease in Thailand

Abstract

Pyricularia oryzae is a plant pathogenic fungus causing rice blast disease. In Thailand, there is very little information about pathogenicity and avirulence gene of rice blast pathogen. Each of the 50 blast isolates obtained from blast disease samples collected from 19 provinces was investigated for avirulence gene on 31 near isogenic lines (NILs) and their pathotype on elite rice cultivars was determined using 24 Thai elite rice cultivars. Among the 50 isolates, Avr-Pita-2 was discovered mostly in isolates from the North (83%), Avr-Pikp and Avr-Pi7(t) were discovered in isolates from the North East (94%), while 8 avirulence genes including Avr-Pikp, Avr-Pikh, Avr-Pi1, Avr-Pi7(t), Avr-Piz, Avr-Pi12, Avr-Pi19 and Avr-Pi20 were discovered in isolates from the South (88%) and Avr-Pi9 was discovered in isolates from the Central region of Thailand (71%). Isolates BRM60001 that carried the most numbers of Avr gene was unable to infect any elite rice cultivars, while isolates that carried as less as 2 Avr genes could infect few elite rice cultivars. Isolate CRI59004.1 carried Avr-Pik (Avr-Pikh, Avr-Pikm, Avr-Pi7(t)), Avr-Pi9, Avr-Pish, Avr-Pib, Avr-Piz-5, Avr-Pita, Avr-Pita-2 and Avr-Pi19, could infect the greatest numbers of elite rice cultivars. The information regarding the distribution of Avr gene in P. oryzae will be useful for forecasting rice blast and disease resistance breeding programs.