POLLEN-OVULE RATIOS AND BREEDING SYSTEM EVOLUTION IN SOLANUM SECTION BASARTHRUM (SOLANACEAE)

Pollen-ovule ratio, pollen grains per flower, pollen grain volume, pol len biomass, ovules per ovary, seeds per fruit, seed volume, seed biom ass, and corolla size were studied to reveal patterns of variation wit hin a monophyletic group. Solanum sect. Basarthrum includes 22 neotrop ical species of two clades, one having small, few-seeded red fruits, a nd the other having larger, many-seeded green fruits. The former inclu des self-incompatible species and a dioecious species, while the latte r includes self-incompatible species, self-compatible (and autogamous) species, and a domesticate (the "pepino"). Although the pollen quanti ty and ovule quantity of the self-incompatible species are significant ly higher in the green-fruited subgroup than in the red-fruited subgro up, the pollen-ovule ratios of the self-incompatible species are not s ignificantly different between the two subgroups, suggesting parallel evolution of the pollen-ovule ratio. Furthermore, the pollen-ovule rat io tracks the breeding system: self-incompatible species have signific antly higher pollen-ovule ratios than self-compatible species, resulti ng both from fewer pollen grains and more ovules of the latter. The po llen-ovule ratio of the dioecious species is among the highest of all, resulting only from fewer ovules. The pepino is self-compatible but h as a pollen-ovule ratio like its wild self-incompatible progenitors an d shows wide variation in seed production and pollen quality, but not in pollen quantity. Among all species, pollen size and quantity are in versely proportional, as are seed size and quantity.