Within-cluster hand-thinning increases fruit Weight in north American pawpaw [Asimina triloba (l.) Dunal]

1 Co-Investigator of Horticulture, Atwood Research Facility, Kentucky State University, Frankfort, KY 40601-2355 2 Principal Investigator of Horticulture and Curator, USDA National Clonal Germplasm Repository for Asimina species, Atwood Research Facility, Kentucky State University, Frankfort, KY 40601-2355. To whom reprint requests should be addressed. Abstract Pawpaw [Asimina triloba (L.) Dunal] is a tree fruit native to the Eastern United States with increasing popularity as a high-value niche crop. Two undesirable characteristics of pawpaw are great variation in fruit size and short shelf-life, caused in part by a small tear in the skin created when fruit are harvested from the cluster, allowing pathogens to enter the fruit. Within-cluster thinning of pawpaw to one fruit could increase fruit size and improve shelf-life by allowing the peduncle to be cut at harvest, maintaining an intact epidermis. The objectives of this study were to determine if hand thinning of multi-fruit clusters to one fruit could be accomplished without causing abortion of the remaining fruit and to determine if within-cluster thinning would increase average fruit size. In a preliminary experiment with seedling trees in 2004, hand thinning of clusters to a single fruit did not lead to cluster abortion or greater drop rates than unthinned clusters. Mature trees of four pawpaw cultivars were utilized in a fruit thinning study in 2006 and 2008. Trees were hand thinned in early-June, and fruit were harvested from mid-August through late-September. Fruit from hand-thinned trees weighed significantly more than those from control trees (47% and 23% greater weight in 2006 and 2008, respectively). Crop density, yield efficiency, and fruit number per tree tended to be or were significantly higher for unthinned trees. Number of clusters per tree, trunk cross-sectional area, yield, and the percent cluster drop and fruit drop, were not significantly different for thinned and unthinned trees. In pawpaw, as in other tree fruits, fruit thinning increases fruit size by reducing competition among and within clusters.