Characterization of Alternaria alternata Isolates from Tangerine Hybrids Affected by Brown Spot in Italy

Alternaria brown spot, caused by Alternaria alternata, is the most important disease of tangerines and their hybrids worldwide, including Italy. The disease represents, for some susceptible citrus cultivar, a limiting factor in profitable cultivation. The results of the characterization of A. alternata isolates obtained from lesions on leaves and fruits of Fortune, Nova and Winola hybrids and Valencia sweet orange, collected in two groves located in Calabria and Sicily, is reported. An endopolygalacturonase gene (endoPG) was sequenced from five representative strains and a phylogenetic tree based on endoPG sequence data of Italian isolates and those of citrus associated Alternaria species deposited in Genbank was constructed. Italian brown spot isolates were grouped both in clusters with brown spot isolates from different countries and in clusters with A. alternata isolates associated with other diseases of citrus. Intra-population variability was demonstrated by a fAFLP protocol. A primer pair combination was selected amongst four primer combinations and tested on 18 A. alternata isolates. Mixed populations of A. alternata were recovered in a single citrus grove in Calabria. No correlation was found among geographical origin, host, and year of isolation.