First Report of Bacterial Apical Necrosis of Mango Caused by Pseudomonas syringae pv. syringae in Greece

The mango, Mangifera indica L., native to India and Southeast Asia, is grown throughout the tropics and subtropics and marketed as fresh or processed fruit contributing greatly to those countries’ income. According to FAO database, from 2007 to 2012, mango production in Greece reached 438 tonnes, an increase of 338% indicating a strong economic potential for the cultivation (FAO 2017). During spring of 2014 and 2015, symptoms similar to those of bacterial apical necrosis disease caused by Pseudomonas syringae pv. syringae (Pss) were observed on commercial mango orchards planted with cv. Irwin throughout two growing areas in Chania, Crete, Greece. The disease was characterized by rapidly expanding necrotic lesions on leaves, buds, stems, and floral panicles, whereas fruits were unaffected. Lesions on leaves started as interveinal, angular, water soaked spots that may coalesce, becoming black and slightly raised. Isolations were made from affected buds, leaf petioles, and necrotic lesions on the leaf and stem. Isolations were made from surface-disinfested symptomatic tissues macerated in sterile phosphate buffered saline (PBS). Cream colored and fluorescent bacterial colonies were consistently isolated from the buds, stem tips, leaf petioles, and leaf tissues adjacent to midribs and interveinal lesions. Ten isolates causing positive hypersensitivity reaction on tobacco plants (Nicotiana tabacum cv. Xanthi) were used for further characterization. The isolates from mango were identified based on their biochemical phenotypic profile, molecular analysis of gyrB gene, and by pathogenicity tests. Isolates were Gram-negative, fluorescent on King’s medium B, catalase positive, levan positive, oxidase negative, potato soft rot negative, and arginine dihydrolase negative. Thus, their profile in LOPAT tests were (+ - - - +), classifying them as belonging to P. syringae LOPAT group Ia. Similar classification was affirmed also with the biochemical tests according to Schaad et al. (2001). Genomic DNA was extracted from the three isolates and amplification of partial gyrase subunit B (gyrB) was performed as described by Trantas et al. (2013). The gyrB DNA sequences of the three isolates TEI277, TEIC279, and TEIC281 (GenBank accession nos. KY091661, KY091662, and KY091663) phylogenetically located them among other strains identified as Pss isolated from Mango (strains UMAF2026, UMAF9981, DAR77787, homologies >99% and 99%, respectively) but partially diverged from the species type strain, which showed ∼94% identity to the type strain of Pss (CFBP1392). Pathogenicity tests were performed on young mango detached leaves, bean pods, immature lemons, and tomato seedlings. Inoculations were made by placing 15 μl drops of bacterial suspension (106CFU ml–1in PBS) on freshly wounded tissues with disease symptoms been observed within 10 days. Controls were treated with sterile PBS. Koch’s postulates were fulfilled and bacteria were reisolated from infected necrotic tissues stably identified as Pss. To our knowledge, this is the first report of P. syringae pv. syringae strains causing bacterial apical necrosis on mango in Greece. © 2017, American Phytopathological Society. All rights reserved.