found in the understory of hardwood forests and low fruit set has been reported in wild patches (4, 8). Low light levels in the understory may limit flower bud formation during the previous summer. If flowers are formed and successfully pollinated, low light levels may also reduce photosynthate partitioning to fruit and reduce fruit set. Pawpaws in the wild often produce many root suckers, forming large clonal patches, thus leading to poor fruit set within a patch due to flower self-incompatibility. Pollinator limitation may also lead to low fruit set in wild patches (8). Because the pawpaw flowers are protogynous (8), lack of pollen availability from other pawpaw genotypes may also limit pollination. Pollinizer relationships among pawpaw cultivars have not been examined. Fruit set can be enhanced by hand cross-pollination (5).

We tested a number of hypotheses during this study concerning pawpaw fruit production and flowering, including: 1) an extended flowering period on the same tree will lead to greater fruit set, 2) a larger number of flowers on a tree will result in a greater number of fruit on that tree, and 3) fruit set is low in pawpaw. The objectives of this study were to determine if mature trees of commercially available pawpaw cultivars display: 1) concentrated bloom periods, 2) late flowering characteristics, 3) high fruit set, and 4) concentrated fruit ripening characteristics that were related to concentrated bloom periods.

Materials and Methods

In 2004, 2005, and 2006, flowering and fruit set characteristics were evaluated for the commercially available cultivars ‘Middletown’, ‘Overleese’, ‘PA-Golden’, ‘Sunflower’, ‘Wells’, and ‘Wilson’ (Table 1). In 2005 and 2006 the cultivar ‘NC-1’ and the Paw-Paw Foundation (PPF) advanced selection 2-54 were also evaluated. The trees used in this study were part of a pawpaw regional variety trial (PRVT) that was planted in late March, 1998 in a Lowell silt loam soil (pH 6.9) at the KSU Research Farm in Frankfort, KY (7). The PRVT planting consists of about 300 trees, with five to eight replications (blocks) of 28 grafted scion varieties per block in a randomized complete block design (10 commercially available cultivars and 18 clones selected in the PPF orchards at the University of Maryland Experiment Stations at Queenstown, Md. and Keedysville, Md.). Seedlings from native Kentucky trees serve as border row trees. Trees were fertilized with Peters 20-20-20 (20 N-8.7 P-16.6 K) water-soluble fertilizer four times each year, in May, June, July, and August, for a total of 12.1 kg N •ha-1 (10.8 lbs N/ac). Supplemental irrigation was provided as needed via drip irrigation.

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fruit set characteristics were evaluated for the commercially available cultivars ‘Middletown’, ‘Overleese’, ‘PA-Golden’, ‘Sunflower’, ‘Wells’, and ‘Wilson’ (Table 1). In 2005 and 2006 the cultivar ‘NC-1’ and the Paw-Paw Foundation (PPF) advanced selection 2-54 were also evaluated. The trees used in this study were part of a pawpaw regional variety trial (PRVT) that was planted in late March, 1998 in a Lowell silt loam soil (pH 6.9) at the KSU Research Farm in Frankfort, KY (7). The PRVT planting consists of about 300 trees, with five to eight replications (blocks) of 28 grafted scion varieties per block in a randomized complete block design (10 commercially available cultivars and 18 clones selected in the PPF orchards at the University of Maryland Experiment Stations at Queenstown, Md. and Keedysville, Md.). Seedlings from native Kentucky trees serve as border row trees. Trees were fertigated with Peters 20-20-20 (20 N-8.7 P-16.6 K) water-soluble fertilizer four times each year, in May, June, July, and August, for a total of 12.1 kg N •ha-1 (10.8 lbs N/ac). Supplemental irrigation was provided as needed via drip irrigation.

Flowers were counted on individual trees for the selected varieties three times a week during April and May in 2004, 2005, and 2006. Fruit clusters were counted in June and late July. Fruit were harvested from individual trees three times a week as they ripened during the harvest season of mid-August to late September. Trunk diameters were measured at 30 cm from ground level in March of each year prior to bloom. The graft union

Table 1. Genetic background of pawpaw clones examined in this study.