Pollen presentation, pollen-ovule ratios, and other reproductive traits in Mediterranean Legumes (Fam. Fabaceae - Subfam. Faboideae)

We studied the allocation of reproductive resources in 32 Mediterranean legume species. Correlations between main parameters were analysed at interspecific level. For each species we described the type of pollen presentation and examined its systematic significance. The high P/O values observed reflect low pollen transfer efficiency, typical of xenogamous species. Lowest P/Os were found in species with brush or explosive tripping mechanism, while highest ones were associated to primary pollen presentation. No trade-off was observed between P/O and the volume of a single pollen grain, nor between pollen number and pollen grain volume. Perennials showed higher P/Os compared to annuals, in accordance with the assumption that annual species are often self-compatible while most perennials are outcrossers. Fruit and seed set, evaluated in eight species under different experimental conditions, showed a close dependence on insects, and the existence of self-compatibility in three species (Colutea arborescens, Coronilla emerus, Hedysarum coronarium). In Colutea arborescens and Coronilla emerus pollen-pistil interaction and pre-zygotic barriers to selfing were investigated through stigma receptivity tests and in-vivo pollen germination trials. Results demonstrated the importance of the stigmatic cuticle in reducing levels of autogamy. Productivity tests confirmed the utility of P/O ratio as indirect measure of species' breeding system.