Abstract
Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo), is a very destructive rice disease worldwide. The aim of the present study was to examine if the Xoo virulence pathotypes obtained using phenotypic pathotyping could be confirmed using molecular approach. After screening of 60 Operon primers with genomic DNA of two Xoo isolates (virulent pathotype, Vr and mildly virulent pathotype, MVr), 12 Operon primers that gave reproducible and useful genetic information were selected and used to analyze 50 Xoo isolates from 7 West African countries. Genetic analysis revealed two major Xoo virulence molecular type (Mt) which were Mta and Mtb with Mta having two subgroups (Mta1 and Mta2). Mta1 (Vr1) subgroup genotype has occurrence in six countries and Mta2 (Vr2) in three countries while Mtb genotype characterized mildly virulence (MVr) Xoo isolates present in five countries. The study revealed possible linkage and correlation between phenotypic pathotyping and molecular typing of Xoo virulence. Durable resistance rice cultivars would need to overcome both Mta and Mtb Xoo virulence genotypes in order to survive after their deployment into different rice ecologies in West Africa. Key words: Bacterial leaf blight, Xanthomonas oryzae pv. oryzae (Xoo), Xoo virulence pathotype, molecular typing, genomic DNA, Operon primer, Xoo virulence genotype, Xoo pathogen migration, West Africa.
Highlights
Rice is one of the most widely cultivated food crop worldwide, but its production is constrained by fungal, bacterial and viral diseases
After screening of 60 Operon primers with genomic DNA of two Xanthomonas oryzae pv. oryzae (Xoo) isolates, 12 Operon primers that gave reproducible and useful genetic information were selected and used to analyze 50 Xoo isolates from 7 West African countries
Durable resistance rice cultivars would need to overcome both Mta and Mtb Xoo virulence genotypes in order to survive after their deployment into different rice ecologies in West Africa
Summary
Rice is one of the most widely cultivated food crop worldwide, but its production is constrained by fungal, bacterial and viral diseases. Some selected Xoo isolates have shown high level of pathogenicity and virulence on the cultivated rice varieties (Sere et al, 2005; Onasanya et al, 2009; Dewa et al, 2011). Recent research has provided considerable evidence that the deployment of bacterial antagonists to Xoo might be an effective strategy, bringing about disease suppression by biological control (Gnanamanickam, 2009).To understand the epidemiology and ecology of Xoo pathogens and their potential for virulence change, various phenotypic characters as well as molecular markers have been used in studies of Xoo pathogen population structure (Jiang et al, 2006). PCR is increasingly becoming an important tool in population biology, because of its simplicity and potential to rapidly screen a large number of samples with a minimal amount of DNA
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