Abstract
Bacterial leaf blight (BLB) of rice is a very destructive disease worldwide and is caused by Xanthomonas oryzae pv. oryzae (Xoo). 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 genotypes (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. Xoo virulence genotypes were known to exist within country and there was evidence of Xoo pathogen migration between 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.
Highlights
Rice is perhaps the most widely cultivated food crop world over, but its production is constrained by diseases of fungal, bacterial, and viral origins
The main goal of this study is to determine Xanthomonas oryzae pv. oryzae (Xoo) virulence genotypes using the characterized Xoo isolates virulence pathotypes identified by Onasanya et al [4] using random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) assays
After screening of 60 Operon primers with genomic DNA of two Xoo isolates, only 12 primers gave reproducible polymorphism and useful genetic information that differentiated the fifty Xoo isolates
Summary
Rice is perhaps the most widely cultivated food crop world over, but its production is constrained by diseases of fungal, bacterial, and viral origins. The disease is known to occur in epidemic proportions in many parts of the world, incurring severe crop loss of up to 50% [1, 2, 4]. Crop loss assessment studies have revealed that this disease reduces grain yield to varying levels, depending on the stage of the crop, degree of cultivar susceptibility, and, to a great extent, the conduciveness of the environment in which it occurs [6]. The severity and significance of damage caused by infection have necessitated the development of strategies to control and manage the disease, so as to reduce crop loss and to avert an epidemic. 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 [9]
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