Highbush Blueberry Cultivars Differ in the Relationship between Seed Number and Berry Weight during the Harvest Season

Abstract

The relationship between individual berry weight and viable seed number of small- (<15 mm), medium- (15–19 mm), and large-diameter (>19 mm) berries was studied over 2 years in nine cultivars (Aurora, Bluecrop, Bluegold, Draper, Duke, Liberty, Legacy, Ozarkblue, and Reka) through their harvest seasons. Plants were grown with two different preplant amendment-mulch treatments, but this treatment had no effect on the variables measured, so data were pooled. The highest average seeds/berry was in ‘Bluecrop’ (55.5) and ‘Duke’ (50.0) and the lowest in ‘Bluegold’ (17.1), ‘Aurora’ (22.5), and ‘Liberty’ (23.5). Average berry weight over the fruiting season ranged from 1.79 and 1.80 g for ‘Liberty’ and ‘Reka’, respectively, to 2.30 and 2.44 g in ‘Ozarkblue’ and ‘Draper’, respectively. The average number of seeds/berry was higher in 2010 than in 2009 for all cultivars, ranging from 14% higher in ‘Reka’ to 96% higher in ‘Liberty’. The flowering period was earlier in 2010 than in 2009, but bloom was concentrated in 2009 (28 days) compared with 2010 (45 days), likely affecting pollinator success. In general, seeds/berry and berry weight declined through the harvest season. Some cultivars had a considerable difference in the number of seeds in large-sized than in small-sized berries (e.g., 89%, 107%, 108%, and 147% more seeds in ‘Aurora’, ‘Reka’, ‘Bluegold’, and ‘Liberty’, respectively), whereas others had relatively little difference (14% and 36% in ‘Draper’ and ‘Bluecrop’, respectively). There was a linear relationship between berry weight and viable seeds/berry. Cultivars did not differ in the berry weight per seed (slope of the line) between the 2 years, except for ‘Draper’ (only significant in 2009), ‘Legacy’, and ‘Reka’. ‘Bluegold’ had the greatest berry weight per seed and ‘Reka’ the lowest. The weakest relationship between berry weight and seed number was in ‘Draper’. Cultivars that produced parthenocarpic fruit of marketable size were ‘Aurora’, ‘Bluegold’, and ‘Liberty’. ‘Duke’, ‘Legacy’, ‘Reka’, and ‘Ozarkblue’ produced commercially acceptable fruit (0.75–1.0 g) with fewer than 7 seeds/berry. By contrast, some cultivars required a relatively large number of seeds to produce a berry including ‘Bluecrop’ (28–40 seeds), ‘Draper’ (15–23 seeds), and ‘Legacy’ in 2010 (20 seeds). The number of seeds per berry accounted for as much as 87% of the variability in berry weight indicating the importance of good pollination and seed set for berry weight and yield in these cultivars.