MALE-FERTILITY OF DERIVED TETRAPLOIDS OF SOLANUM-TUBEROSUM FROM GROUPS TUBERSOSUM-X PHUREJA-STENOTOMUM

Four plants of each of 15 derived tetraploids from a cross of B0749-2F (2n=4x=48) and DM91-5 (2n=2x=24) were planted in the greenhouse at Be ltsville, Maryland, in January 1992. The female tetraploid parent is a late blight resistant selection from the Tuberosum germplasm base. Th e male diploid parent is a high dry matter selection from the Group Ph ureja-Stenotomum germplasm base. For each derived tetraploid, the perc ent normal, abnormal, and total pollen germination in vitro were deter mined on 2-4 flowers per derived tetraploid harvested 3-4 times during a three-week period in April. The percent normal, abnormal, and total pollen germination ranged from 0.6 to 27.5, 0.1 to 7.6, and 1.4 to 36 .6, respectively. Pollen tube growth, measured 2 hours from initiation of germination, ranged from 22 to 130 nm. Four general types of abnor malities in the pollen were identified: a) stunted and curly pollen tu bes; b) damaged membranes allowing leakage of cytoplasmic contents; c) pollen grains with two or more pollen tubes; and d) split pollen tube s. In hybridizations with Atlantic as the female parent, 11 out of 15 of these derived tetraploids produced viable seeds. All 15 derived tet raploids were female fertile. These results suggest that utilizing der ived tetraploids from the Tuberosum and Phureja-Stenotomum germplasm b ases in future breeding efforts should not present any great difficult y. However, hybridizations involving these derived tetraploids were mo re successful when the derived tetraploids were the female parent.