Heterosis and Expressivity of Apospory in Tetraploid Bahiagrass Hybrids

Abstract

Breeding procedures developed for apomictic species are based on the idea of fixing superior hybrids by apomixis. However, scarce information is available about the occurrence of heterosis in apomictic hybrids. The objective was to generate a group of apomixis‐segregating tetraploid bahiagrass (Paspalum notatum Flüggé) families, evaluate the occurrence of heterosis for a series of agronomic and morphological traits, determine the level of apospory expressivity among hybrids, and estimate the genetic distance among parents and its relationship to heterosis and apospory expressivity. In total, 11 tetraploid families were generated by crossing sexual and apomitic genotypes. The segregation for mode of reproduction was analyzed using a random amplified polymorphic DNA (RAPD) marker linked to apospory in bahiagrass, and the level of apospory expressivity was determined using embryo sac observations. The genetic distances between parents were determined using inter‐simple sequence repeat (ISSR) markers. The ratio between sexual and aposporic hybrids varied from 1:1 to 7:1 among families. Discontinuous variation for apospory expressivity was observed in the hybrids, with either low or high levels being exhibited. Midparent, high‐parent, and standard heterosis was observed for all evaluated characteristics. The level of heterosis was dependent on the combination of parents involved and also on the specific trait. There was a low correlation between genetic distances among parents and initial growth and the level of apospory expressivity. The occurrence of heterosis and the segregation and expressivity for apospory were highly dependent on the combination of sexual and apomictic parents.

Breeding apomictic bahiagrass (Paspalum notatum Flügge) with improved turf traits

“…, , Zilli et al. ). The average segregation ratios for mode of reproduction reported in bahiagrass (sexual:aposporic) 4:1 (Acuña et al.…”

“…) and 3.2:1 (Zilli et al. ) indicate that a very low proportion of obligate apomictic hybrids are recovered in the progeny of such crosses, limiting the applicability of this approach in bahiagrass breeding. Additionally, the potential for sexuality found in facultative apomictic bahiagrass (Martínez et al.…”

“…Obligate apomictic ecotypes have been introduced into the United States, including the cultivar 'Argentine' . In order to overcome the barrier to recombination imposed by apomixis, sexual tetraploid plants were created by chromosome doubling (Forbes and Burton 1961, Quarin et al 2001) and used as females in crosses to produce tetraploid hybrids , Zilli et al 2015. The average segregation ratios for mode of reproduction reported in bahiagrass (sexual:aposporic) 4:1 (Acuña et al 2011) and 3.2:1 (Zilli et al 2015) indicate that a very low proportion of obligate apomictic hybrids are recovered in the progeny of such crosses, limiting the applicability of this approach in bahiagrass breeding.…”

Mode of reproduction and meiotic chromosome behavior in Acroceras macrum

“…Pistils at immature stages came from florets on branches below the source of mature pistils and above the source of young pistils. Pistils were clarified following the instructions described in Zilli et al (2015) with some modifications, and embryo structures were observed. Modifications were as follows: pistils were kept 30 min in a 10% H 2 O 2 solution for a first bleaching.…”

Breeding Tetraploid Paspalum simplex: Hybridization, Early Identification of Apomicts, and Impact of Apomixis on Hybrid Performance

“…The progeny resulting from crosses between compatible sexual and apomictic genotypes is usually highly diverse for agronomic traits (Acuña et al, 2011; Zilli et al, 2015; Weiler et al, 2018). The primary advantage of crossing sexual and apomictic strains is that the hybrid progenies segregate for mode of reproduction and traits of interest are fixed over generations (Hanna, 1995).…”