Intra-regional diversity of rice bacterial blight pathogen,Xanthomonas oryzaepv.oryzae, in the Andaman Islands, India: revelation by pathotyping and multilocus sequence typing

Aim To investigate the genetic and pathogenic variability ofXanthomonas oryzaepv.oryzaecausing bacterial blight in rice on the remote Andaman Islands, India. Methods and Results A total of 27 yellow-pigmented bacterial isolates representing rice fields of Andaman Islands incited blight on the susceptible-rice cultivar, C14-8. Phenotypic, pathogenic traits and 16S rRNA gene sequences revealed their identity asX. oryzaepv.oryzae. Virulence profiling indicated the prevalence of seven pathotypes ofX. oryzaepv.oryzaeon the Islands. Pathotypes-VI and -VII were highly virulent, whereas the pathotype-I was less virulent. Multilocus sequence typing based on nucleotide sequence polymorphism in nine housekeeping genesdnaK;fyuA;gyrB (two loci):rpoD;fusA;gapA;gltA andlepA clustered 27 isolates into 17 sequence types (STs) segregated into two clonal-complexes (CC). While CC-I comprised of isolates from Andaman Island, the CC-II is a mixture of isolates representing mainland India and Andaman Island. The data revealed trans-boundary pathogen introduction and a consequent intra-regional diversification on these islands due to the deployment of different rice cultivars in different regions. Conclusions Genotyping and pathotyping of sland isolates revealed seven pathotypes distributed in two clonal complexes with strong indications for trans-boundary movement and consequent diversification of the bacterial pathogen. Highly virulent pathotypes ofX. oryzaepv.oryzaethat could overcome combinations of R-genes,xa13+Xa21 as well asxa5+xa13 were found prevalent in the Andaman Islands Significance and Impact of the Study Genetic and virulence analysis ofX. oryzaepv.oryzaein the Andaman Islands revealed introduction and host-mediated regional diversification and local adaptation ofX oryzaepv.oryzae. The study calls for the need of multi-gene pyramiding for durable disease resistance and establishing stringent quarantine measures for safeguarding island agricultural practices in the future.

Automated summary

This study investigated the genetic and pathogenic variability of Xanthomonas oryzae pv. oryzae causing bacterial blight in rice on the remote Andaman Islands. Results showed the presence of seven pathotypes distributed in two clonal complexes, indicating trans-boundary movement and consequent diversification of the bacterial pathogen. The study emphasizes the importance of multi-gene pyramiding for durable disease resistance and establishing stringent quarantine measures for safeguarding island agricultural practices in the future.