FIRST REPORT OF AUREOBASIDIUM PULLULANS AS A POSTHARVEST DISEASE OF 'ABATE FETEL' PEARS FROM AN ORGANIC ORCHARD IN RIO NEGRO, ARGENTINA

‘Abate Fetel’ pears harvested in the first week of February 2013 from an organic orchard in Rio Negro, Argentina, developed rot disease with particular characteristics 15 days after cold storage. The aim of this work was to isolate and identify the causal agent of this pathology. The pathogen was isolated from pears with symptoms and incubated in the dark at 22°C. Pathogenicity tests were done in ‘Abate Fetel’, ‘Packham’s Triumph’ and ‘Golden Russet Bosc’. The microorganism was identified by its morphological characteristics. 95% of the isolates were pink colonies with irregular margins, which in time turned dark, with mycelium submerged in the cultivation media, slow growth (20 mm in 7 days), smooth, flat, covered with slimy masses of conidia. Hyaline conidia of variable shape and size, 2-3 µm, were observed through a microscope. These characteristics coincide with the description of Aureobasidium pullulans (de Bary) Arnaud. In the fruit, symptoms began with small irregular brown spots of 2 to 3 mm, with a depressed, circular darker center that slowly increased in size, firm, developing into the pulp a few mm. Pathogenicity tests with Aureobasidium were only positive in ‘Abate Fetel’. Aureobasidium pullulans has been reported as a biocontrol agent. Generally, it is found in a saprophytic state and rarely as a pathogen. This is the first report as a pathogen in pears in the Río Negro Valley.