Relative success of self and outcross pollen after mixed- and single-donor pollinations in Eucalyptus grandis

Abstract

A previous observation that self-pollen tubes traversed the style at a slower rate than cross-pollen tubes in Eucalyptus grandis and E. urophylla suggested the presence of cryptic self-incompatibility (CSI) in these species. The aim of the present study was, with the help of molecular markers, to examine the siring ability of self- and cross-pollen in a single clone of E. grandis, after both mixed- and single-donor pollinations, in order to confirm the presence of CSI. Single-donor cross-pollinations set a significantly higher number of seeds per flower pollinated compared to those performed with self-pollen, while there were no significant differences between the open control and single-donor self-pollinations. Molecular markers revealed that 100% of the progeny from mixed-donor pollinations were outcrossed, confirming the competitive advantage of cross-pollen. In addition, there was a significant change in the self:outcross seed ratio between single- and mixed-donor pollinations, suggesting that the observed deficit of selfed seeds in mixed-donor fruits could be the result of differential pollen tube growth. From the extremely low seed yields following single-donor self-pollinations, it is clear that an additional incompatibility mechanism is operating in E. grandis, and this is suggested to be late-acting self-incompatibility, acting before fertilisation.