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SPECIAL SESSION: Plant Pathologists of the Future: Showcasing Graduate Student Presentation Winners from APS Division Meetings

Moldy Core of Apple caused by Alternaria spp. in Chile: Identification, characterization and potential inoculum source
Karina Elfar - Pontificia Universidad Catolica de Chile. Juan P. Zoffoli- Pontificia Universidad Catolica de Chile, Bernardo Latorre- Pontificia Universidad Catolica de Chile

Apple (Malus domestica) is a major fruit crop in Chile. Among apple diseases, moldy core (MC) has a high prevalence (16 to 46%) in cultivars with an open sinus from the calyx to the core region in Chile. Infected fruits are characterized by the presence of a gray to dark olive-green mycelium restricted to the carpel without necessarily affecting the fruit flesh. This study aims to identify and characterize the major fungal pathogens associated with MC and to investigate the potential inoculum sources. In 2015-2017, 11 orchards were surveyed. Isolations revealed numerous fungal species associated with MC, being the Alternaria spp. the most frequently and consistently isolated fungi (67.7%), followed by Cladosporium, Penicillium, Stemphylium, Epicoccum, Botrytis, and Fusarium. Out of 330 isolates, six small-spored Alternaria species were identified morphologically and molecularly namely, in order of importance, A. tenuissima, A. arborescens, A. alternata, A. dumosa, A. frumenti and A. kordkuyana. These Alternaria spp. were pathogenic, producing a gray to dark olive-green mycelium over the carpel and seed of immature and mature apples. These isolates caused brown necrotic lesions with concentric rings on wounded apple leaves. Alternaria spp. were found colonizing sepals, stamens and carpels of apparently healthy flowers and fruits sampled, from pink bud to the mature fruit. This study demonstrated that at least six small-spored Alternaria spp. are the cause of apple MC in Chile and that apparently healthy flower and fruit may be important inoculum sources for MC infections.