Preferential outcrossing in the complex species Persoonia mollis R. Br. (Proteaceae)

The breeding system of the extremely diverse species Persoonia mollis (Proteaceae) was characterized to, firstly, assess its importance as a mechanism promoting diversity and, secondly, to investigate the mode of control over selective fruit abortion. Fruit quantity and quality was assessed following self-and outcross-pollination manipulations. Twenty percent of outcrossed flowers set fruit, compared to only 1% of flowers fertilized with self-pollen. Fruits produced by self-fertilization were 72% of the weight of cross-fertilized fruits. Fruits produced by self-fertilization were significantly fewer in number and lighter than fruits following natural pollination of unmanipulated flowers (17% fruit set), but outcrossed and naturally pollinated fruits were equivalent. Flower to fruit demography suggested that a post-zygotic mechanism may be preferentially selecting the most vigorous zygote genotypes, as ovary abscission occurs mostly between 4 and 30 weeks after pollination, regardless of pollen source. Self-pollen tube growth was found to be inhibited within the styly, while pollen tubes were found in the ovary for 50% of all outcrossed flowers. These data suggest that a pre-zygotic "pseudo" self-incompatibility mechanism is the cause of low fruit set following self-pollination. The breeding system of P. mollis was found to promote outbreeding, with an emphasis on flexibility and post-zygotic choice following pre-zygotic "pseudo" self-incompatibility.