Bull's eye rot of apple fruit caused by Neofabraea alba

Abstract

Bull's eye rot caused by Neofabraea spp. is an important postharvest disease of apple fruit worldwide. Four species of the genus are known to cause this disease among which Neofabraea alba is the main pathogen causing bull's eye rot in continental Europe. Typical symptoms of the disease were observed in a local market in Belgrade, Serbia in March 2015. Circular lesions, slightly sunken light brown to dark brown with a lighter brown to tan center and a darker outer ring were present on 'Golden Delicious' apples. Decayed tissue was firm. The aim of this study was to identify the causal agent of bull's eye rot of apple fruit based on morphological and molecular characteristics of the pathogen. Two fungal isolates were obtained using standard laboratory procedure and their pathogenicity was tested by wound inoculation of healthy 'Idared' apple fruit. Seven days post inoculation lesions up to 23 cm in diameter developed on inoculated fruit while control fruit remained healthy. The isolates were preliminary identified based on colony morphology. They formed round, slow growing colonies on potato dextrose agar (PDA) with initially white mycelium which turned pinkish-brown with time. Cylindrical to curved-fusiform macroconidia were formed. Microconidia were not observed. Species level identification was completed by sequence analysis of the partial beta-tubulin gene. MegaBLAST analysis of the obtained nucleotide sequences (622 nt) revealed 100% and 99% similarity with several Neofabraea alba sequences deposited in GenBank. Based on morphological characteristics and the partial sequence analysis of p-tubulin gene, Neofabraea alba (Guthrie) Verkley was identified as the causal agent of bull's eye rot of apple fruit in Serbia.