Abstract
Bacterial blight (BB) caused by X. oryzae pv. oryzae is one of the devastating diseases of rice mostly in Asia. Genomes of X. oryzae pv. oryzae is highly variable due to rearrangement of the large contents of transposable elements and dynamic changes of X. oryzae pv. oryzae population regulated efficiency of the control measures used for BB management of rice worldwide. In this study, genetic variation of X. oryzae pv. oryzae pathotypes of Bangladesh was studied using aviruelnce gene based RFLP and rep-PCR techniques aimed to formulate pathogen targeted effective control measures against BB of rice. Eight pathotypes of X. oryzae pv. oryzae field isolates were identified based on their reactions against 10 Near Isogenic Lines (NILs). Among eight pathotypes, pathotypes IV and V contained higher number of isolates which were 30.13% and 23.01% respectively while pathotype VIII revealed as minimum containing only 2.51% of total isolates. These eight pathotypes were studied for their genetic variation by RFLP using avrBs3 repeat domain as probe. The results conceded that Bangladeshi X. oryzae pv. oryzae strains seem carrying a minimum of two and maximum of nine avrBs3 family genes homologs. The resistance phenotype on IRBB7 and IRBB10 NILs also indicated presence of two major avrBs3 family genes viz. avrxa7 and avrXa10 in some pathotypes. Relationship of phylogenicity exhibited that X. oryzae pv. oryzae pathotypes assorted into two RFLP haplotypes as well as these haplotypes are largely distributed in Bangladesh. Phylogenetic analyses carried out by (REP, ERIC), rep-PCR and BOX depicted the presence of two main molecular haplotypes of X. oryzae pv. oryzae pathotypes. The relationship between pathotypes and molecular haplotypes of X. oryzae pv. oryzae in Bangladesh indicated that the same lineage possesses different pathotypes and different lineage possesses different pathotypes. The results indicated that eight different pathotypes might have originated from common inherited haplotypes with a wide genetic variation.
Highlights
Co-evolution of reciprocal, ‘‘arms race’’ like relationship between bacterial pathogens and their hosts for adaptation has been observed during plantmicrobe interactions (1, 2)
In different growth stages of rice plant BLB appears, disease symptoms predominantly exhibit on leafs showing leaf blight or revealing wilting symptoms of young plants which has been known as Kresek, to infect such way, wound or water pores are served as a prime invading option for the pathogen X. oryzae pv. oryzae lesions with wavy edges emerge from the leaf tip and margins and coalesce and enlarge in size, turn yellow, and dying of the plant (12). 20 to 40% reduction of yield was accounted when plants infected at tillering stage with the highest rate (13)
X. oryzae pv. oryzae isolates were confirmed by PCR EcoR1 genomic DNA fragments of these eight pathotypes of amplification of genomic DNA of the 8 representative pathotypes (I-VIII) and negative control was maintained with nuclease-free water
Summary
Co-evolution of reciprocal, ‘‘arms race’’ like relationship between bacterial pathogens and their hosts for adaptation has been observed during plantmicrobe interactions (1, 2). Bacterial pathogens overcome host defence or to establish successful infection in novel hosts through the development of new virulence factors such as effectors by maintaining a high level of ge-. Up to 50% yield reduction was manifested in the early detection of bacterial blight disease in rice (14). Throughout the last few years, a serious BB epidemic happened in many areas of Bangladesh with substantial yield losses of around 50-70% especially in irrigated hybrid varieties possibly due to the emergence of new races of its pathogen (15). It has been reported the pathogenic variability of X. oryzae pv. Damage due to BB increased significantly following the widespread cultivation of high yielding and nitrogen-responsive dwarf hybrid varieties of rice in the 1960s (20)
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