PERCENT DRUPELET SET VARIES AMONG BLACKBERRY GENOTYPES

Twenty-one genotypes of blackberry (Rubus L. subgenus Rubus Watson) we re evaluated for percent drupelet set in 1993 and eleven genotypes wer e evaluated in 1994, Commercial cultivars were chosen to represent typ es (trailing, erect, and semi-erect) of blackberries grown in the Unit ed States. Secondary fruit were picked when green but developing a red blush during the early- and late-ripening season. Drupelets and pisti ls per fruit were counted to calculate percent set, In 1994, ripe frui t ranging in size were harvested for 'Boysen', 'Marion', 'Thornless Ev ergreen', and 'Chester Thornless' and drupelet per fruit were counted. Drupelet set among genotypes ranged from 40% to 86% in 1993 and 39% t o 78% in 1994. Most genotypes had a higher percent set on early flower s compared to later ones. Drupelet set and number were not correlated with fruit weight among genotypes. In 'Boysen', 'Marion', 'Thornless E vergreen', and 'Chester Thornless', drupelet number was correlated wit h fruit weight, although the relationship in 'Chester Thornless' was n ot as strong as the others, It is unclear what factors limit drupelet set in the genotypes studied.