English

Abstract

We investigated the distribution of Xanthomonas citri subsp. citri (Xcc) pathotypes in south-western region of Saudi Arabia. A total of 76 Xanthomonas like strains were isolated from different citrus species showing bacterial canker symptoms from citrus commercial farms, backyard orchards and nurseries. These strains were subjected to biochemical, molecular and pathogenicity tests on leaves of grapefruit (Citrus paradisi). Based on symptoms induced on leaves of grapefruit, these strains were divided into two groups. There were 21 strains that induced typical erumpent canker lesions with water-soaked margin, belonging to Xcc type A. On the other hand, strains that produced flat necrotic lesions with water-soaked margin on grapefruit leaves belonged to Xcc A* type (55 strains). The physiological and biochemical tests, ImmuneStrip ® assays and 16S rDNA analysis confirmed the identity of the two Xcc pathotypes: A and A*. Our results indicate that, the two pathogenic variants co-exist in south-western region of Saudi Arabia and this could further favour the generation of new genetic variants through recombination and horizontal genetic exchange. The generation of new aggressive pathotypes may threaten the citrus plantation in Saudi Arabia. Key words: Disease diagnosis, pathogenicity, citrus bacterial canker.