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POSTERS: New and emerging diseases

Marssonina Blotch of Apple Caused by Marssonina coronaria in New York
Sr?an A?imovi? - Cornell University, Hudson Valley Research Laboratory. Fatemeh Khodadadi- Cornell University, Hudson Valley Research Laboratory, Daniel Donahue- Cornell Cooperative Extension, Eastern New York Commercial Horticulture Program, Kari Peter- Pennsylvania State University, Fruit Research and Extension Center

Marssonina blotch (MB) is a fungal disease of apple leaves and fruit caused by Marssonina coronaria (Ellis & Davis) Davis (teleomorph Diplocarpon mali Harada & Sawamura). Favored by excessive number of rain events in 2017 and 2018, MB is a rising problem in apple production of New York and eastern United States leading to premature tree defoliation and fruit infections at the end of summer. To identify the causal pathogen, we isolated fungi from symptomatic apple fruit of cultivar (cv.) ‘Rome’ on peptone potato dextrose agar at 25ºC in darkness. The five recovered isolates uniformly showed slow growing dark grey colonies after three weeks of incubation. The phylogenetic analysis by sequencing of the conserved regions of 5.8S rRNA and internal transcribed spacer (ITS) revealed that our isolates were 99% similar to Marssonina coronaria reference strains in NCBI GenBank. High sequence similarity (98~100%) among our isolates confirmed these results. Pathogenicity test on 4-month-old potted apple seedlings (cv. Rome) inoculated with suspension of 1 × 106 conidia ml ?1 and placed in humid conditions showed small dark brown to black spots developed on leaves 10 days after inoculation. Our results for the first time confirm the presence of MB caused by M. coronaria on apple in New York.