Morphological and Molecular Variability among Rice Blast Pathogen (Magnaporthe oryzae) Isolates in Southern India

摘要

Rice is a staple food crop for majority of human population worldwide. Significant grain yield losses are reported due to blast disease caused by Magnaporthe oryzae across all crop growing areas of the world. Though, presently available blast management strategies reduce disease significantly, blast epidemics are still common, thereby causing devastating yield losses. Our present study therefore aimed at determining variability among blast pathogenic isolates that ultimately enables formulation of area-wise blast management strategies, besides preventing indiscriminate usage of chemical fungicides. Leaf blast samples were collected from crop growing areas of Telangana and Andhra Pradesh during kharif 2014 and 2015 and M. oryzae (n=20) isolates wereobtained using standard laboratory protocols. These isolates were further evaluated for their morphological and genetic characterization. In morphological studies, variability was determined based on colony diameter, color and shape of conidia under in vitro conditions. Genetic diversity was determined based on molecular methods using PCR with 3 MGM markers. Our results indicated that morphologically, the blastpathogenic isolates differed and their colony diameter ranged from 71.6 to 87.6 mm. On oat meal agar, colony color of the isolates was usually grey and greyish-white with good growth. Genetic diversity studies on M. oryzae isolates using 3 MGM markers indicated less polymorphism at DNA level. The cluster analysis of MGM data grouped the isolates on the basis of their origin with few exceptions. A total of seven amplicons were obtained from 20 M. oryzae isolates. Cluster analysis of the blast isolates revealed the average pair-wise similarities in the range of 0.08 to 1.0, thus suggesting variations among the isolates. Our research results on variability of blast pathogen will be useful in devising location specific disease management strategies for rice blast.