First report of stem-end russeting in apple fruits caused by the yeast-like fungus of Aureobasidium pullulans in Iran

A tan colored, corky tissue was appeared on the skin of the fruit surface in the stem-end cavity, approximately 30 days after full blooming stage at the same time of rapid growth of epidermal cells in fruits and continued until the fruits fully grown. 30 samples with symptoms were brought to the laboratory during the growing season. For pathogenicity, conidial suspension was prepared in sterile distilled water with an approximate concentration of 1010 spores per ml of the single spores colonies and one ml of the above suspension was poured onto stem-end cavity of the scraped and non-scraped fruits, 4 fruits for each group. In the cavity of 4 fruits, distilled water without spores was poured, and in the cavity of 4 other fruits, no solution was poured. Fruits were kept in humid environment for 40 days. All fruits inoculated with spore suspension showed symptoms similar to orchard conditions whereas, in other fruits no symptoms were observed. The hyphae were transparent, with transverse walls and 2–10 μm thick. The single-celled conidia were transparent, smooth, and elliptical and varied in shape and size. Their size ranged 7.3 4 4.8 × 4.8–7 μm, similar to range reported by Zalar et al. (2008). The two-celled conidia were translucent to dark brown and their size ranged 15-24 × 6–10 μm. Comparing morphological characteristics of colonies, hyphae and conidia with literaturea yeast-like fungi, Aureobasidium pullulans, was detected as The causative agent of the stem-end russeting on golden delicious and red delicious fruits.