Pollinator limitation and late-acting self-incompatibility mechanism as causes of low fruit set in two sympatric species of Inga (Fabaceae - Mimosoideae) in the Central Amazon

Abstract

The breeding system of Inga edulis Mart. and Inga stipularis D.C. was studied in an area of forest, located in the UFAM Experimental Farm, Manaus, AM, from November/2006 to November/2007. The results showed that both species do not set fruit from self-pollination and that the percentage of fruit set proceeding from cross-pollination in I. edulis (5%) and I. stipularis (21%) is superior to the natural pollination (control), 1% and 7%, respectively. The analyses of pollen tube, originating from self-pollination and cross-pollination, reveal that a small fraction reaches the ovules of I. edulis after 8 and 12 hours, and in I. stipularis 24 hours after pollinations. In addition there is a greater percentile of tubes penetrating in the ovules of I. edulis. The arrival speed of the tubes in the ovules deriving from self-pollination and cross-pollination is similar in both species. The low indices of fruit set in I. edulis and I. stipularis probably is a result from the raised index of geitonogamy promoted by the pollinators and the late-acting self-incompatibility.