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 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 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 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. Mid-parent, high-parent, and standard-heterosis was observed for all evaluated agronomic 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.