Pistachio (Pistacia vera L.) canker caused by Pantoea agglomerans

Pistachio (Pistacia vera L.) is a perennial woody plant that produces edible seeds with a high nutritional value. Canker disease is one of the important diseases of pistachio, causing considerable loss globally. During 2019–2021, a series of symptoms, including tree weakness, brown to black lesions, canker, and exudation of black sap were observed on the trunk of pistachio trees from different regions of Lorestan province, western Iran. Bacterial isolation resulted in the development of uniform and yellow colonies on yeast-extract peptone glucose agar (YPGA) medium 24 h post-inoculation (hpi). The colonies were then purified on YPGA and yeast-extract-dextrose-calcium-carbonate agar (YDC). Based on the analysis of morphological, biochemical, and molecular characteristics using nucleotide sequences of the gyrB, infB, atpD, and 16S rRNA, a putative pathogen was identified as Pantoea agglomerans (formerly Enterobacter agglomerans). To fulfill Koch's postulates, bacterial suspensions (107 CFU/ml) were inoculated to one-year-old pistachio seedlings. Thirty days after inoculation, small necrotic lesions developed on the bark in the vicinity of inoculation sites, followed by brown necrotic streaks in the inner bark. Subsequently, the bacterial strains exhibiting the characteristic colony morphology were retrieved from lesions on inoculated pistachio seedlings and verified as P. agglomerans. To the best of our knowledge, this is the first report on the occurrence of pistachio canker caused by P. agglomerans.