Percent drupelet set varies among blackberry genotypes

Twenty-one genotypes of blackberry (Rubus L. subgenus Rubus Watson) were evaluated for percent drupelet set in 1993 and eleven genotypes were evaluated in 1994, Commercial cultivars were chosen to represent types (trailing, erect, and semi-erect) of blackberries grown in the United States. Secondary fruit were picked when green but developing a red blush during the early- and late-ripening season. Drupelets and pistils per fruit were counted to calculate percent set, In 1994, ripe fruit ranging in size were harvested for 'Boysen', 'Marion', 'Thornless Evergreen', and 'Chester Thornless' and drupelet per fruit were counted. Drupelet set among genotypes ranged from 40% to 86% in 1993 and 39% to 78% in 1994. Most genotypes had a higher percent set on early flowers compared to later ones. Drupelet set and number were not correlated with fruit weight among genotypes. In 'Boysen', 'Marion', 'Thornless Evergreen', and 'Chester Thornless', drupelet number was correlated with fruit weight, although the relationship in 'Chester Thornless' was not as strong as the others, It is unclear what factors limit drupelet set in the genotypes studied.