Bud pollination and other techniques are ineffective in breaking late-acting self-incompatibility in Ceiba chodatii (Malvaceae - Bombacoideae)

ABSTRACT There are two homomorphic self-incompatibility (SI) mechanisms among flowering plants - gametophytic self-incompatibility (GSI) and sporophytic self-incompatibility (SSI). Whilst SI has the advantage of promoting outbreeding in natural populations, it can also be a problem for horticulturists and agronomists. Thus, a number of techniques have been successfully employed to break both GSI and SSI, including bud pollination, saline pre-treatment of the stigmas and simply selfing ageing flowers. We applied these three techniques to determine whether they would be effective at breaking SI in Ceiba chodatii, a species with late-acting self-incompatibility (LSI). We self- or cross-pollinated buds ranging from 1-4 days prior to anthesis and checked ageing by selfing or crossing flowers at 1-4 days after the onset of anthesis, with those at four days showing petal wilt. None of the selfed buds or ageing flowers set fruit, unlike the majority of crossed flowers. Likewise, all flowers to which 1 % saline was applied to the stigmas prior to selfing failed to set fruit. We conclude that unlike GSI and SSI, which have pre-zygotic control of self-pollen function, LSI is likely to be immune to these techniques since the focus of rejection occurs after self pollen tubes have reached the ovary.