Alternaria spp. on apparently healthy apples as a potential inoculum source for moldy core development and the effect of resistant and susceptible apple cultivars

Apple ( Malus domestica Borkh) is a major fruit crop in Chile. Among apple diseases, moldy core (MC) in the fruit has a high prevalence (16 to 46%) in susceptible cultivars. Apparently healthy flowers and fruit were sampled at six growth stages, from the pink bud to the mature fruit, from the susceptible ‘Oregon Spur’ and from the resistant ‘Granny Smith’ apples during two growing seasons. At least seven fungal genera were detected colonizing flowers and the fruit of both cultivars. Small-spored Alternaria spp. were the primary species identified throughout all the growing stages. Independently of the growth stages, sepals, stamens and carpels of flowers were similarly colonized by Alternaria spp. in the susceptible (‘Oregon Spur’) and resistant (‘Granny Smith’) apple cultivars. However, in fruits of 4–6 cm in diameter, big differences in the frequency of Alternaria spp. in fruit carpels were observed between susceptible and resistant apples, with 55% and 1%, respectively. At least five Alternaria spp. were identified at the species level using plasma membrane ATPase, namely, A. alternata , A. arborescens , A. limoniasperae , A. tenuissima in sect Alternaria , A. kordkuyana in sect. Pseudoalternaria and Alternaria sp. in sect. Infectoriae . All Alternaria isolates, from sepals, stamens and carpels, from apparently healthy flowers and fruits were pathogenic, producing MC symptoms in apples. These results suggest that apparently healthy flowers and fruits may act as an important inoculum source of Alternaria spp. for MC infections and also suggest that control strategies against MC using fungicide applications should be carried at flowering, from pink bud onwards.