Staphylococcus warneri, an unconventional plant pathogen involved in canker disease of almond and other Prunus species

Bacterial canker disease of stone fruits is a major concern in stone fruit‐growing countries worldwide. Pseudomonas spp. and Xanthomonas arboricola pv. pruni (Xap) are the primary pathogens involved in this disease. In spring, summer and autumn 2016, symptoms like those produced by Pseudomonas spp. and Xap were observed in almond, apricot, peach and nectarine orchards in central provinces of Iran (Qom, Isfahan, and Chaharmahal and Bakhtiari). Gram‐positive cocci bacterial isolates were obtained from symptomatic trees. Following hypersensitivity and pathogenicity tests, isolates were divided into pathogenic and nonpathogenic groups, demonstrating the pathogenicity of some isolates on saplings of almond, peach and apricot. Multilocus sequence analysis was performed using the partial sequence of 16S rRNA region and four housekeeping genes, namely tuf, gap, dnaJ and rpoB, to determine the taxonomic classification of isolates, and revealed that pathogenic isolates identified as Staphylococcus warneri, while nonpathogenic isolates identified as S. warneri, S. epidermidis, S. hominis and S. saprophyticus. The isolates were further characterized by phenotypic and biochemical tests as well as by antibiotics assays. The unusual nature of the identified microorganism in the present study lies in the fact that, unlike most plant‐pathogenic agents, S. warneri is recognized worldwide as a cause of bacterial infections in humans and animals. Taken together, the bacterial canker disease caused by S. warneri appears to be a newly emerging disease of apricot, peach and almond trees.