Etiology of Leaf Spot and Fruit Canker Symptoms on Stone Fruits and Nut Trees in Iran

During July 2015 to June 2017, 63 walnut and 94 stone fruit orchards were surveyed in Iran to identify and characterize the causal agent of a disease inducing leaf spot and fruit canker symptoms. Altogether, 189 Prunus spp. and 141 walnut samples (i.e. leaves, branches and fruits) were collected from 10 Provinces in northern, northwestern, central and southern Iran. Forty-three yellow-pigmented Gram-negative bacterial isolates were recovered from symptomatic plants. Only seven bacterial strains isolated from walnut in Mazandaran and Golestan Provinces were identified as X. arboricola pv. juglandis based on pathogenicity assays, specific PCRs, and multilocus sequence analysis. Based on the phenotypic features and phylogenetic analysis of gyrB gene sequences, strains isolated from stone fruit trees were identified as multiple Pantoea species (i.e. P. agglomerans, P. ananatis, P. vagans and P. pleuroti). None of these strains caused symptoms on Prunus spp. plantlets tested under greenhouse conditions. Although the occurrence of bacterial blight of walnut in Iran was ascertained using molecular-phylogenetic analysis, no evidence was obtained that the observed disease was the same as the bacterial spot and canker of stone fruits caused by X. arboricola pv. pruni in the country.