also differed between populations, with accessions from Washington Co., Indiana, West Virginia, and Kentucky exhibiting a later harvest peak than trees from New York or Decatur Co., Indiana. Growing degree days varied significantly between accessions, with trees from New York requiring the fewest GDDs to ripen, 2262, and the other 5 populations requiring a similar number of GDDs (2400-2500) for ripening.
A correlation was found in 2004 between the total number of flowers produced by a tree and the total number of fruit clusters produced by that tree (r=0.39, Table 5.11). Trees which flowered for a longer period of time did not produce more clusters per tree or a higher yield by weight. An earlier flower peak led to an earlier harvest peak (r=0.26), but there was no correlation between length of flowering and length of harvest. Neither longer flowering time nor total number of flowers led to a higher percentage of fruit set on trees. A larger trunk cross sectional area did positively affect the total number of flowers per tree (r=0.60), total yield by weight (r=0.29) and total number of fruit per tree (r=0.33), but did not affect percentage fruit set or yield efficiency. Again, correlations by individual state varied greatly (Table 5.12), with few correlations that were significant across all populations being significant by individual population.
This study is the first of its kind to characterize vegetative and reproductive traits in pawpaw populations from various geographic regions under the same environmental conditions. Trees possessing desirable traits such as large fruit size, good flavor, texture, storability, color break at ripening, early and/or late ripening, late flowering to avoid spring frosts, concentrated flowering time, concentrated ripening time, high fruit set, more single fruited clusters, and high fruit yields could be used in breeding efforts in the development of new pawpaw cultivars by the KSU USDA-NCGR for Asimina species. Developing new pawpaw cultivars with these features is key to the growth and development of a commercial pawpaw industry (Peterson 1991; Peterson, 2003).
Pawpaw seedlings normally begin to flower when the trees reach about 1.8 m, but may not set fruit; cropping is achieved at five to eight years (Pomper et al., 2003). Grafted pawpaw trees often flower within 3 years after planting, but fail to set fruit (Pomper et al. 2003; Bratsch et al. 2003; Merwin et al. 2003). Failure of trees to set fruit could be due to inadequate pollination or inadequate canopy development to support fruit