Floral biology and the effects of plant-pollinator interaction on pollination intensity, fruit and seed set in Solanum

Abstract

Reproductive biology and patterns of plant-pollinator interaction are fundamental to gene flow, diversity and evolutionary success of plants. Consequently, we examined the magnitude of insect-plant interaction based on the dynamics of breeding systems and floral biology and their effects on pollination intensity, fruit and seed set. Field and laboratory experiments covering stigma receptivity, anthesis, pollen shed, load and viability, pollinator watch vis-à-vis controlled self, cross and pollinator-exclusion experiments were performed on nine taxa of Solanum: Solanum aethiopicum L., Solanum anguivi Lam., Solanum gilo Raddi, Solanum erianthum Don, Solanum torvum SW, Solanum melongena L. (‘Melongena’ and ‘Golden’) and Solanum scabrum Mill. (‘Scabrum’ and ‘Erectum’). Pollen shed commenced 30 min before flower opening attaining peak at 20 to 30 min and continued until closure. Stigma was receptive 15 to 30 min before pollen release, making most species primary inbreeders (100% selfed) but facultatively outbreeding (12.5 to 75%) through insect pollinators such as Megachile latimanus, Diplolepis rosae and Bombus pennsylvanicus. S. scabrum ‘Scabrum’ was an obligate inbreeder, while S. scabrum ‘Erectum’ was facultatively outbreeding (12.5%). S. melongena ‘Melongena’ was strongly outcrossing (75%) than its relative ‘Golden’ (25%). Small pollen and anther assured high pollen load and pollination efficiency and vice versa, except S. torvum. Diploid species (2n = 24) received crossed pollen (25 to 53.9%) from related species than the tetraploid S. scabrum (2n = 48; 0 to 11%). We concluded that insect-pollinators complement self pollination in Solanum. They provide cross-pollen, which enhanced gene exchange and hybrids in natural population and lower inbreeding depression.

Key words: Breeding system, hybridization, insect pollinator, outcrossing, pollination, Solanum.