Detection and Induction of Unreduced Pollen in a Begonia Collection

Meiotic polyploidisation can be used to create genetic variation in plant breeding. To use 2n gametes in an efficient way, a reliable and easy screening method is necessary. In our research 4 main techniques for the detection of 2n pollen were compared on 70 different Begonia genotypes: pollen size measurements, flow cytometric screening of pollen DNA, evaluation of microsporogenesis and ploidy level of the progeny. Unreduced pollen could be detected in 10 genotypes, with frequencies depending on the genotype and the used method.
The major drawback to use 2n pollen in a breeding program, is that only the minority of the plants produce these gametes. And even if they are present, their frequency is usually too low to be of practical use. Therefore, different techniques (temperature stress, use of the cell cycle disruptor Trifluralin or N2O-treatment) were tested either to induce 2n pollen production or to raise their frequency in Begonia. Temperature stress only increased the frequency, while the two other methods induced aberrant pollen. Especially the use of N2O treatments looks promising as it could produce viable 2n pollen in male sterile interspecific genotypes.
The advantage of meiotic versus mitotic polyploidisation is now more studied by comparing crossing population resulting from crosses between Begonia soli-mutata x Begonia ‘Orococo’ (producer of unreduced gametes) and between Begonia soli-mutata x Begonia ‘Orococo’ (mitotically chromosome doubled).