Variability in pathogen population and pyramiding of resistance genes against bacterial blight of rice caused by Xanthomonas oryzae pv oryzae

Abstract

Rice is the most important food crop in India and several other countries newlineespecially in Asia. Due to changes in cultivation practices there have been newlineincreased incidences of different pests and diseases. Many diseases earlier newlineconsidered as minor, are becoming serious ones over the years. Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo), remains a major production constraint in rice cultivation especially in irrigated and rainfed lowland ecosystems in India. The pathogen is highly dynamic in nature and many rice cultivars especially those carrying single resistance genes have become susceptible in different rice growing areas of India. Breeding for broad spectrum and durable resistance against BB by pyramiding multiple resistance genes is the most effective strategy for managing the disease. Based on the above information, present investigation entitled Variability in pathogen population and pyramiding of resistance genes against Bacterial blight of Rice caused by Xanthomonas oryzae pv. oryzae was designed. In the present study, a total of 400 isolates of Xoo collected from diverse rice growing regions of India were analyzed for pathogenic and genetic variability. These Xoo isolates were characterized for their virulence profile by inoculating them on a set of differentials consisting of 22 near isogenic lines (NILs) possessing different BB resistance genes either singly or in combinations in the background of rice variety IR24. The varieties like TN1 (susceptible check) and Improved Samba Mahsuri (resistant check) were also included in the experiment. Based on their reactions on the differentials, these isolates were categorized into 22 pathotypes. Among 22 pathotypes 1 and 2 were least virulent and 18-22 pathotypes were highly virulent. Molecular analysis was carried out using two primers complementary to sequence of IS1112, a newlinerepetitive element isolated from Xoo using PCR. A high level of genetic polymorphism was detected among these isolates and grouped into 9 major clusters.