Serratia marcescens associated with squash leaf chlorosis and necrotic spots in Iran

Abstract

In autumn 2011, a survey was conducted for the identification of plant pathogenic bacteria affecting Cucurbitaceae grown in southwestern Iran. Squash (Cucurbita pepo var. styriaca) plants with suspected bacterial symptoms, i.e. necrotic spots surrounded by chlorotic haloes, were collected and brought to the laboratory for further analysis. Two Gram-negative, red-pigmented bacterial strains were isolated from squash leaves in Shushtar county, Khuzestan province. The isolates induced hypersensitive reaction (HR) on tobacco plants 24 h post-inoculation. A pathogenicity test on 25-day-old squash plants yielded symptoms consisting of necrotic spots surrounded by chlorotic haloes that appeared 5–10 days post-inoculation. The causal agent was identified as Serratia marcescens based on biochemical and phylogenetic analyses. Phylogenetic analysis of 16S rRNA, gyrB and groE genes sequences showed that the isolates have 99–100% similarity with S. marcescens strains previously described as pathogenic to bell pepper and corn plants. Although non-pigmented strains of S. marcescens have previously been described as the causal agents of cucurbit yellow vine disease, this is the first report of a HR-inducing red-pigmented strain of the bacterium associated with squash leaf chlorosis and necrosis.