Induction of 2n pollen formation in Begonia by trifluralin and N2O treatments

In this study, treatments of both trifluralin (at 10, 100 and 1000 μM) and N₂O (in the form of gas under pressure) were applied to Begonia flower buds to induce the formation of 2n pollen. Three male fertile species (B. cucullata, B. subvillosa var. leptotricha and B. fischeri) and two male sterile hybrids (B. schmidtiana × B. cucullata and B. subvillosa var. leptotricha × B. cucullata) were treated. Pollen size, which is related to pollen DNA content, increased after both N₂O and trifluralin treatments, but the induction of large pollen was genotype dependent. Trifluralin induced large pollen only in the male fertile species, while N₂O treatments induced fertile 2n pollen in the male sterile B. schmidtiana × B. cucullata. Cytological studies showed that trifluralin induced multinuclear monads that resulted in 4n gametes in stead of 2n gametes. In general, large pollen obtained after trifluralin treatments showed low germination capability, while large pollen obtained after N₂O treatments retained high germination capability. Seedlings with raised ploidy level could only be obtained after crosses were performed with large pollen obtained from N₂O treatments. Hence, N₂O treatments are preferable to the use of trifluralin to induce 2n gametes in Begonia.