The 2012 ASHS Annual Conference

A leaf and fruit fungal spot has been observed in pawpaw consisting of a complex of Mycocentrospora asiminae, Rhopaloconidium asiminae Ellis and Morg., and Phyllosticta asiminae Ellis and Kellerm. Symptoms include tan spots with dark brown borders on leaves, and dark brown to black superficial spots on the fruit epidermis. Leaves displaying these symptoms were collected from plantings at the Kentucky State University Research Farm and positively identified as Phyllosticta leaf spot by the University of Kentucky Plant Diagnostic Lab. Cracking is occasionally observed on pawpaw fruit. It was hypothesized that there may be a correlation between incidence of Phyllosticta fruit spot on pawpaw and fruit cracking, due to epidermal damage by the fungus. The objective of this study was to determine if Phyllosticta fruit spot and cracking incidence varied by cultivar, and if there was any correlation between fruit spot occurrence and fruit cracking. Ripe fruit were harvested three times per week from a mature pawpaw planting consisting of two pawpaw cultivars (Sunflower and Susquehanna) grafted onto seedling rootstock. Percent coverage by Phyllosticta fruit spot was visually estimated, and fruit cracking was evaluated for each fruit harvested.  In 2010, a positive correlation was found between cracking and Phyllosticta coverage. However, in 2011, no correlation was seen. Susquehanna fruit exhibited more cracking than Sunflower in 2010. Susquehanna also had a larger fruit size than Sunflower, which could lead to greater tendency to crack. Other factors could also be related to fruit cracking, such as firmness and thickness of the epidermis. Sunflower was found to have greater Phyllosticta fruit spot damage in 2010, but not 2011. Future studies are needed to determine the relationship between Phyllosticta fungal fruit spot and fruit cracking in pawpaw, and to determine varietal resistance to this fungus and possible control measures.