New insight into morphological and genetic diversity of Phlyctema vagabunda and Neofabraea kienholzii causing bull's eye rot on apple and pear

Fungi of genera Phlyctema and Neofabraea are the causal agents of bull's eye rot, a major postharvest disease of pome fruits. To investigate their morphological and genetic diversity, isolates obtained in Italy and Chile from decayed fruit and rainwater between 2014 and 2019 were grown on two agar media, inoculated onto four fruit cultivars and compared using four marker genes. Consistent intra- and interspecies phenotypic differences were recorded among isolates identified as P. vagabunda (two main morphotypes, PvM-I and PvM-II, were distinguished) and N. kienholzii. In particular, the Chilean isolates belonging to PvM-I showed low sporulation in vitro, while isolates belonging to PvM-II showed the most abundant sporulation and also formed conidiomata deep within fruit tissue. Host cultivar influenced the disease incidence in unwounded, inoculated fruit. Cripps Pink and Golden Delicious apples favoured the formation of P. vagabunda conidiomata and macroconidia, while Granny Smith apples and/or Kaiser pears restricted sporulation of some isolates of PvM-I. Mycelial cords of P. vagabunda and N. kienholzii were consistently recorded in inoculated fruit, suggesting their possible involvement as a source of inoculum. Propagules of P. vagabunda were present in rainwater collected from apple plants from September to October in Italy. According to sequence analysis of ITS, EF-1α, TUB2 and ACT1 regions of the fungi, 12 distinct sequence types were identified, three of which were characteristic of isolates from the Southern Hemisphere. The condensed maximum-likelihood phylogenetic tree separated the 50 P. vagabunda isolates into six phylogroups, suggesting a correlation with their geographical distribution.