Impact of Self- and Cross-pollination on Fruit and Seed Set in Pawpaw in Kentucky

Pawpaw (Asimina triloba) is a native tree fruit that is in small-scale production across much of the eastern and southern portions of the United States. There is some evidence that pawpaw requires cross-pollination; however, there is also evidence of self-compatibility or self-fruitfulness in some cultivars. The objective of this study was to determine the incidence of self-compatibility and its impact on fruit and seed set in pawpaw. Two pawpaw cultivars, Sunflower and Susquehanna, were examined in this study at the Kentucky State University Harold R. Benson Research and Demonstration Farm. Approximately 1000 crosses, including 250 self- and cross-pollinations for each cultivar, were carried out with open flowers in Apr 2016 and 2017. Competing flowers were removed after pollination, and the number of fruit clusters and fruit number within each cluster were recorded three times a year during May, July, and August. The fruit were harvested in August, followed by seed extraction. After stratification, the seeds were sown in a greenhouse. The leaves of parent material and the newly germinated seedlings from the seeds in each treatment were collected and DNA was extracted. Primers for three pawpaw simple sequence repeats (SSRs) for the loci Pp-B3, Pp-B103, and Pp-G124 were selected. These primers generated unique SSR fingerprint patterns for each parent and allowed the determination of whether a seedling was the result of selfing or crossing between the two parents. This study is the first to report that selfing can occur in pawpaw. The DNA fingerprinting results confirmed some self-fruit set in ‘Sunflower’ in 2016 and 2017. Both cultivars served as pollinizers for the other; however, genetic yield potential by the maternal tree could be more important for determining the ultimate fruit set than outcrossing between genotypes.