ORIGINAL ARTICLE Alternaria spp. on apparently healthy apples as a potential inoculum source for moldy core development and the effect of resistant and susceptible apple cultivars Karina Elfar & Juan P. Zoffoli & Bernardo A. Latorre Accepted: 8 July 2019 # Koninklijke Nederlandse Planteziektenkundige Vereniging 2019 Abstract 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 gen- era 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, sta- mens 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 ob- served between susceptible and resistant apples, with 55% and 1%, respectively. At least five Alternaria spp. were identified at the species level using plasma mem- brane 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 appar- ently 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. Keywords Apple diseases . Core rot . Malus domestica . Epidemiology Apple (Malus domestica Borkh) is commercially impor- tant crop, being the second most planted fruit crop tree, at present with 35,937 ha, representing 11% of the total fruit crops in Chile. Among apple diseases, moldy core disease is an economically important disease that occurs primary in open sinus apple cultivars such us ‘Oregon Spur’,’ Red Chief ’ and ‘Scarlet’. The symptoms are characterized by the presence of a gray to dark olive green cottony mycelium that grows in the carpels and over the apple seeds. Prevalences from 16 to 46% were estimated at harvest in the 2015–2017 growing seasons in Chile. Moldy core is more difficult to find in close sinus cultivars such as ‘Granny Smith’ and ‘Golden Deli- cious’ (Elfar et al. 2018b; Niem et al. 2007; Serdani et al. 1998). At least six small-spored Alternaria spp. have been associated with moldy core in Chile, namely, A. alternata, A. arborescens, A. dumosa, A. frumenti, A. kordkuyana and A. tenuissima, with the latter species being the most frequently isolated species (Elfar et al. 2018b). Eur J Plant Pathol https://doi.org/10.1007/s10658-019-01802-2 K. Elfar (*) : J. P. Zoffoli : B. A. Latorre Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Casilla, 306-22 Santiago, Chile e-mail: kdelfar@uc.cl