Interspecific hybridization between Banksia hookeriana Meisn. and Banksia prionotes Lindl (Proteaceae)

Abstract

Interspecific hybridization of Banksia hookeriana and Banksia prionotes was investigated via pollen tube growth, seed set, morphological measurements, and analysis of RAPD polymorphisms. Pollen tube growth to the ovary was observed following selfing and crossing pollination of each species and following interspecific hybridization to B. hookeriana as the female parent, but not in the reciprocal cross. All crosses resulted in seed set, except for self-pollination of B. prionotes and interspecific pollination to B. prionotes as the female parent. Mortality of hybrid seedlings was high RAPD analysis of hybrid seedlings from two families showed paternal B. prionotes bands in all 11 tested seedlings. Leaf length or width of nine hybrid seedlings that survived to the 10-leaf stage was intermediate between that of intraspecific seedlings of both parents at the same age. A mature natural interspecific hybrid was fertile following controlled selfing and backcrossing to each parental species, as well as following open pollination, but seed set was lower than for the parental species. It was concluded that hybridization between B. hookeriana and B. prionotes is unilateral, with interspecific seed set of B. hookeriana comparable to that following intraspecific pollination.