Virulence analysis of Magnaporthe oryzae for resistance gene deployment in northwestern Himalayas

Virulence structure of 122 Magnaporthe oryzae isolates originating from north-western Himalayan states was deciphered using 26 international monogenic differentials representing 23 blast resistance genes in the susceptible genetic background ‘Lijiangxintuanheigu’ (LTH). The pathogen populations from Himachal and Uttarakhand exhibited exceptionally high pathotypic diversity as each of the tested isolates from these regions represented a unique race. The pathogen populations from J&K showed comparatively lower level of pathotypic diversity with 23 races detected amongst the 34 isolates analyzed from the region. The overall highest frequency of virulence was recorded on blast resistance gene Pi-19 followed by Pi-k^s, Pi-7, Pi-k^p, Pi-k, Pi-a, Pi-k^m and Pi-1 on which 50.82 to 87.70% of the isolates were virulent. Although compatibility with most of the rice genotypes tested was observed in the pathogen population, none exhibited susceptibility to all the isolates. LTH, the presumed universal susceptible background used for developing monogenic differentials, showed resistance to 11.61% of the tested isolates. The results suggest that LTH harbours some unknown blast resistance gene(s) that are effective against a subset of virulences prevalent in the region. The matching virulences appropriate to all the rice genotypes except Tetep (Pi-l, Pi-k^h, Pi-ta,) were observed in the pathogen population. A low frequency of virulence (10 to 17.21%) was recorded on blast resistance genes Pi-9, Pi-z, Pi-2, Pi-ta² and Pi-12. Based on present study, various combinations of blast resistance gene(s) have been identified for deployment in different north-western Himalayan states.