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was at a height of 15 cm from the soil line. Values for trunk diameters were converted to trunk cross-sectional area [TCA (cm2)]. The number of fruit on each tree was counted in late July each year following the normal fruit drop period. Growing degree days (GDDs) were calculated using a base temperature of 10circC (University of Kentucky Agricultural Weather Center calculator, http://wwwagwx.ca.uky.edu/calculators.html). Temperature data were obtained from the University of Kentucky Agricultural Weather Center's monthly climate summary (http://wwwagwx.ca.uky.edu/cgi-public/climsum2.ehtml), from temperatures recorded at Lexington.

Data on trunk cross-sectional area, flower number per tree, flower density (number of flowers per tree/TCA), flowering peak (date at which the greatest number of flowers were fully open; when flowers are maroon in color), fruit set, days between flower and harvest peak, duration of flowering, duration of harvest, and yield by cultivar or advanced selection were subjected to GLM analysis of variance, LSD mean separation, and regression analysis using the statistical program Costat (CoHort Software, Monterey, Calif.).

Results

In 2004, 2005, and 2006, TCA differed significantly among cultivars, reflecting variation in vigor among the cultivars (Table 2). Flower number per tree varied among cultivars in each of the three years. There was variation among cultivars in flower density, with ‘Middletown’ tending to produce the most flowers per unit TCA in 2005 and 2006. Significant cultivar differences in fruit set were observed each year. For example, ‘Middletown’ displayed the highest flower density in 2005 and 2006, but the highest fruit set was not observed in this cultivar in either year (Table 2). Yield varied by cultivar in each year. No crop occurred in 2003 due to an April frost event. This likely resulted in a heavy crop for each cultivar in 2004, lower yields in 2005, and high yields again in 2006. ‘PA-Golden’ was the highest yielding cultivar in each year of the study. Peak flowering date, bloom duration period, days between flower peak and harvest peak varied among cultivars during each year of the study (Table 3). Late-flowering cultivars were ‘Middletown’ and ‘Wells’, which were about 8 to 10 days later than the early flowering cultivars ‘NC-1’ and ‘Overleese’, and the advanced selection 2-54 (Table 3). Bloom duration varied among cultivars in all years ranging from 23-36 days (Table 3 and Fig. 1). Significant differences in harvest duration were only found in 2006, and harvest duration varied from 15 to 31 days across all years (Table 3). ‘Middletown’, ‘Wilson’, ‘Overleese’, ‘NC-1’ and ‘Sunflower’, and the advanced selection 2-54 had the longest number of days between flowering peak and harvest peak. ‘PA-Golden’ (New York), ‘Taytwo’ (Michigan), and ‘Taylor’ (Michigan) were selected in the most northern regions and had the fewest days between flowering peak and harvest peak. Fruit weight varied (65 to 189 g) with cultivar and year (Table 3). ‘NC-1’, ‘Overleese’ and ‘Sunflower’ had the largest fruit, averaging over 150 g, and ‘Middletown’, ‘Wilson’, ‘PA-Golden’, ‘Wells’ and the advanced selection 2-54 had fruit weights that averaged less than 150 g.

Peak flowering date, bloom duration period, days between flower peak and harvest peak varied among cultivars during each year of the study (Table 3). Late-flowering cultivars were ‘Middletown’ and ‘Wells’, which were about 8 to 10 days later than the early flowering cultivars ‘NC-1’ and ‘Overleese’, and the advanced selection 2-54 (Table 3). Bloom duration varied among cultivars in all years ranging from 23-36 days (Table 3 and Fig. 1). Significant differences in harvest duration were only found in 2006, and harvest duration varied from 15 to 31 days across all years (Table 3). ‘Middletown’, ‘Wilson’, ‘Overleese’, ‘NC-1’ and ‘Sunflower’, and the advanced selection 2-54 had the longest number of days between flowering peak and harvest peak. ‘PA-Golden’ (New York), ‘Taytwo’ (Michigan), and ‘Taylor’ (Michigan) were selected in the most northern regions and had the fewest days between flowering peak and harvest peak. Fruit weight varied (65 to 189 g) with cultivar and year (Table 3). ‘NC-1’, ‘Overleese’ and ‘Sunflower’ had the largest fruit, averaging over 150 g, and ‘Middletown’, ‘Wilson’, ‘PA-Golden’, ‘Wells’ and the advanced selection 2-54 had fruit weights that averaged less than 150 g.

Correlation analyses performed on all cultivars combined (Table 4) showed a positive linear relationship between TCA and number of clusters, TCA and number of flowers, flower peak and harvest peak, number of flowers and number of fruit clusters, number of flowers and yield, and a negative linear relationship between number of flowers and fruit set in 2004; TCA and number of clusters, TCA and number of flowers, fruit set and yield, and number of flowers and yield in 2005; and TCA and number of flowers, number of flowers and number of clusters, fruit set and yield, and number of flowers and yield in 2006. Using regression analysis, a positive binomial relationship was also found between flower peak and harvest peak in 2006. When combining all data and using regression analysis on the averages of all years, there was a positive linear relationship between TCA and number of clusters, TCA