Phenotypic and genetic characteristics of Xanthomonas citri subsp malvacearum, causal agent of cotton blight, and identification of races in Iran

Bacterial blight was first reported on cotton (Gossypium hirsutum) in Iran in 1972 and has been observed in cotton fields in several provinces with outbreaks occurring in 2004 and 2005. This study was initiated to determine phenotypic characteristics of isolates obtained from diseased cotton plants in two different regions of Iran, discriminate pathogen races and assess the genetic diversity of the pathogen using repetitive-PCR. Thirty-seven isolates were identified as Xanthomonas citri subsp. malvacearum from biochemical and physiological tests. Repetitive-PCR genomic fingerprinting revealed two distinct groups with some variation detected within subgroups. Four different pathogen races were discriminated in pathogenicity tests: race 1 (16%), race 2 (8%), race 6 (57%) and race 18 (19%). There was no genetic distinction between isolates from the two regions suggesting a common inoculum source such as seed.