Widening the Gene Pool of Sexual Tetraploid Bahiagrass: Generation and Reproductive Characterization of a Sexual Synthetic Tetraploid Population

The improvement of bahiagrass, Paspalum notatum Flugge, has been inhibited by reduced levels of genetic diversity in sexual tetraploid germplasm. A few experimental sexual tetraploid genotypes (ESTGs) have been generated by chromosome doubling, but these plants typically exhibit low vigor. The objectives of this work were to generate and characterize the ploidy level, mode of reproduction, and fertility of a novel 308 individual sexual synthetic tetraploid population (SSTP) developed by intercrossing 29 sexual F-1 hybrids originated by hybridizing several naturally occurring apomictic tetraploids from diverse origin with a few ESTGs. Ploidy levels were determined using flow cytometry, and reproductive modes were evaluated by a molecular assay with aposporylinked markers and embryo sac observations. The tetraploid level and the sexual mode of reproduction remained stable after two cycles of recombination during the generation of the SSTP. Fertility was evaluated based on seed set under self-and open pollination during 3 yr. The SSTP exhibited in average 30.2 and 15.2% seed set under open and self-pollination, respectively, showing a predominantly cross-pollination behavior with variable levels of self-fertility. There were no differences in terms of fertility between the SSTP and the ESTG. The novel tetraploid population behaves as sexual and cross-pollinated, and it is expected to allow a more efficient genetic improvement under the proposed breeding approaches.