Archivio Journal of Plant Pathology

Abstract:

In July 2014, symptoms of berry cracking and black rot were observed on bunches of vines grown in a vineyard in the province of Hamedan (Iran). A fungus was successfully isolated from symptomatic berries plated on potato dextrose agar (PDA) incubated at 23°C. Colonies were brownish green with concentric rings, hyphae had pale yellow to brown septa and conidiophores were golden-brown, short, geniculate and sympodial. Conidia (18-20×8-10 μm) were mostly broadly obovoid to subspherical with longitudinal septa, mature conidia were primarily subspherical with few diagnostic obovoid conidia (Woudenberg et al., 2013). Based on these morphological traits, the pathogen was identified as Alternaria cucurbitae. Molecular identification was based on amplification of the β-tubulin gene sequence (Woudenberg et al., 2013). The 550 bp product (GenBank accession No. KU324181), shared 99% similarity with the comparable sequence of A. cucurbitae [=Ulocladium cucurbitae (JQ67200101)]. A pathogenicity test was conducted on detached grapevine bunches (13-15 cm in length). Each sterile Petri dish contained 3 small clusters at the postveraison stage, each with 10 berries, which were sprayed with a spore suspension (1×106 spores/ml), while control samples were sprayed with sterile water. Bunch rot symptoms appeared after 7 days incubation at 25°C. A. cucurbitae was successfully re-isolated from artificially infected berries while the controls remained symptomless. A. cucurbitae has been previously reported as the agent of leaf spot on cucumber in California (Vakalounakis, 1990). To our knowledge, this is the first report of A. cucurbitae as a bunch rot agent on grape in Iran and possibly worldwide.