Pollen-pistil interactions between autotetraploid and diploid Acacia mangium and diploid A. auriculiformis

Development of sterile triploid (3x) planting stock could help manage the risk of invasivity of widely planted Acacia species. Triploids may be derived from crosses of diploid and tetraploid plants. This study investigated the effect of cytotype on pollen-pistil interaction following mating between colchicine-induced tetraploid A. mangium (AM-4x), diploid A. mangium (AM-2x) and A. auriculiformis (AA-2x). Following controlled pollinations, pollen tubes grew well in the style, entered the ovary and penetrated ovules within 72 hours, regardless of the mating type. However, mean number of penetrated ovules per ovary was lower for AM-4x than for AM-2x or AA-2x maternal parents for all cross combinations except for self-pollination. Considering crosses between cytotypes, interspecies had signifcantly greater number of ovules penetrated than intraspecies. However, yields of pods (1.03%) and filled seeds (5.3%) following all inter-cytotype crosses were extremely poor compared with intra-cytotype (7.59 and 76.3% respectively). Thus, there were strong barriers to production of viable 3x seeds, despite the demonstrated absence of pre-zygotic isolation.