Seasonal expression of apospory in bahiagrass

Abstract

Flowering plants can reproduce sexually (outcrossing and/or selfing) and/or asexually. Sexual reproduction implies the successful completion of meiosis and double fertilization for the formation of both the embryo and the endosperm. In contrast, gametophytic apomixis is an asexual mode of reproduction through seeds, that in-volves parthenogenetic embryo development from a cytologically unreduced egg cell (2n). Apospory is the process by which unreduced gametophytes are formed after a series of mitotic divisions of somatic cells (2n) in the ovary. This occurs independently from the sexual meiotic process; and therefore, both sexual and apomic-tic pathways may coexist simultaneously. Apospory is inherited in bahiagrass (Paspalum notatum Flugge) as a single dominant Mendelian factor with distorted segregation (Martinez et al. 2001), and its degree of expression was reported to vary throughout the flowering season in P. cromyorrhizon, a close relative of bahiagrass (Quarin1986). Bahiagrass is a perennial warm-season grass widely used for forage and utility turf in the south-eastern US due to its persistence in sandy, infertile soils. Diploid races reproduce sexually and are highly self-incompatible (Acuna et al. 2007), while polyploids are classified as pseudogamous apomicts (pollination is required) (Quarin 1999). Sexual tetraploid genotypes have been experimentally created (Quesen-berry and Smith 2003; Quesenberry et al. 2010) and suc-cessfully used in crosses (Acuna et al. 2009). Cyto-embryological analysis has been used to determine the mode of reproduction in bahiagrass (Martinez et al. 2001; Acuna et al. 2007). At anthesis, sexual plants pro-duce spikelets having only a single Polygonum type