Seedless fruit production in 'Tosa Buntan' pummelo

Abstract

Effects of streptomycin (SM) spraying on seed production in open pollinated fruit and effects of thinning time and trunk girdling on the set, development and fruit quality were investigated to develop a practical technique for producing seedless 'Tosa Buntan' pummelo. Three spray application of 500 ppm SM to whole trees at 1-5%, 50% and 100% full bloom significantly decreased the number of perfect seeds to 4.5 seeds per fruit. Fruit thinning with leaf/fruit ratio of 90-100 in June 24 (6 weeks after full bloom) promoted the development of open pollinated fruit, yielding mature fruit weighing about 470 g with 5.7 seeds and the soluble solid and citric acid contents statistically the same as those of the hand pollinated control fruits. Trunk girdling on May 1 was ineffective. The combination of three, 500 ppm SM treatments and fruit thinning on June 24, yielded fruit averaging 464 g with 5.7 seeds. Our analysis of the relationship fruit size in June 24 to seed number and fruit size in harvest time, indicate that fruit weighing 450-530 g with about 4 seeds was possibly produced by keeping fruits large as 42-48 mm in diam. when thinning is done about June 24. Our results demonstrate that commercial production of near seedless 'Tosa Buntan' pummelo fruit is possible by 1) three spray treatments with 500 ppm SM at 1-5, 50 and 100% full bloom, 2) fruit thinning in late June, 3) retaining only fruits large as 42-48 mm in diam. and 4) maintaining a leaf/fruit ratio of 90 to 100.