Pollen tube growth and seed set of Banksia coccinea R.Br. (Proteaceae)

Abstract

Controlled hand pollinations and field observations were used in conjunction with fluorescence and scanning electron microscopy and fruit and seed set to investigate the timing of stigma receptivity, pollen tube growth and self-incompatibility in relation to fertility in B. coccinea. The species showed both protandry and partial self-incompatibility. Peak stigma receptivity as measured by pollen germination was recorded at 3 d after anthesis and maximum production of stigmatic exudate at 6 d. Pollen tubes reached the base of the style by 6 d after pollination. A 5 × 5 diallel experiment was conducted and the results measured by pollen tube growth. Self-pollinations generally resulted in poorer tube growth than crosses and there was significant specific and general combining ability as well as reciprocal effects. Cross-pollination resulted in improved fruit set and seed to flower ratio over both selfing and open pollination. Spatial limitations to fertility due to infructescence size were also recorded, but the combination of outcrossing mechanisms and spatial limitation did not entirely account for the low fertility. It is suggested that environmental conditions and the availability of resources may also exert an influence. © 1991 Annals of Botany Company.