Host Dependent and Geographical Structuring of Citrus Canker Bacteria at Peshawar, Pakistan

摘要

Citrus canker disease, caused by Xanthomonas axonopodis pv. Citri (Xac) induces huge losses to citrus, particularly in nurseries. This study assessed the level of genetic diversity and divergence in Xac population prevalent in district Peshawar on various host species, based on isolates collected from different fruit nurseries of Peshawar. Surveillance resulted in collection of 80 samples, out of which 50 bacterial samples were isolated. Genotyping of the isolates using RAPD markers amplified 35 scorable loci with an average of 8.7 loci per primers and level of polymorphism was 100%, i.e., almost all of the isolates genotyped had a different multilocus genotype. The loci GLA-031000 was recorded with the highest gene diversity (0.51) followed by GLB-05_1000 and GLA-03_1100 (0.49). The maximum diversity index (0.50) was recorded for loci GLA- 031000, followed by GLB-051000 and GLA-03_1100 (0.48). A high diversity was observed across all locations, with the range of genotypic diversity from 0.778 (detected at Malakandair) to 0.955 (detected at Hayatabad and Tarnab). Divergence between samples collected from different locations was limited as revealed by the PCA, PCoA, phylogenetic tree and network analyses. Samples originated from various hosts also revealed a high diversity across host types with the minimum genotype diversity observed for Eureka Lemon (0.750) and the maximum for sweet lemon (0.966). The divergence for samples collected on various citrus host types was absent. The very small linkage disequilibrium (0.006–0.159) reflected on the potential recombination in the population, which must have direct implications to disease management and resistance exploitation.