95

and number of flowers, flowering peak and harvest peak, number of flowers and number of clusters, fruit set and yield, and number of flowers and yield. Due to year-to-year inconsistencies and variation among cultivars, no definitive conclusions could be reached concerning correlations between flower and fruiting characteristics in individual pawpaw cultivars.

The average temperature in April was similar in 2004 and 2005, and was warmer in April 2006 (Table 5). May 2005 and 2006 temperatures were similar, with May 2004 being warmer than the following years. GDDs from January 1 to first flower and from January 1 to flower peak, were higher each year of

Table 5. Monthly temperature summary during pawpaw flowering for 2004, 2005 and 2006.

the study (Table 6). GDDs from first flower to peak flower were similar in 2004 and 2006, and were lower in 2005. Flowering peak and duration were not correlated with GDD; in 2006, which had the largest GDDs before flowering and by flowering peak, did not display an earlier flowering peak or shorter duration for most cultivars. The GDDs from

Table 6. Growing degree days (GDDs) during pawpaw flowering across all cultivars calculated using a base temperature of 10circC for 2004, 2005 and 2006.

flower peak to harvest peak were fewer for 2004, than for 2005 and 2006, indicating that these later years had warmer temperatures than 2004. However, the number of days between flowering peak and harvest peak are similar for the tested cultivars.

Discussion

This is the first report of combined flowering and ripening characteristics of commercially available pawpaw cultivars. There was significant variation in year to year flowering and ripening characteristics among the cultivars examined. Mature trees of currently available commercial pawpaw cultivars did not display concentrated bloom periods or ripening periods; however, ‘Wells’ and ‘Middletown’ did have late flowering peaks that could allow a partial crop if early spring frosts destroy flowers around or at the flowering peak. However, the average fruit size of ‘Wells’ and ‘Middletown’ is small (about 100 g; Table 3) and undesirable for commercial production. Based on the data collected in this study, we reject the hypotheses that 1) an extended flowering period on the same tree will lead to greater fruit set and we do not reject hypothesis 2) that a larger number of flowers on a tree will result in a greater number of fruit on that tree. Pollinator limitation has often been suggested as an explanation for low fruit set (<0.5%) in wild patches (8). Fruit set here was greater (5.6%) than that reported in wild pawpaw patches (around 0.5%) (4, 8). Pollinator limitation may reduce fruit set in the wild compared to that in the orchard. Strategies to attract flies to flowering pawpaw orchards could increase fruit set further. Alternatively, pawpaw trees may be able to support a limited number of fruit per tree both in the wild and in orchards and pollinators may not be the limiting factor. Additionally, year to year fruit set may have been influenced by a 2003 frost event that destroyed the pawpaw crop. This likely has resulted in biennial bearing which led to high fruit set in 2004, low fruit set in 2005, and once again high fruit set in 2006. Fruit ripening duration was not related to bloom.