Inheritance of Apospory in Bahiagrass, Paspalum Notatum

Abstract

Previous studies on the inheritance of aposporous apomixis in bahiagrass showed a wide range of segregation ratios in crosses involving sexual and aposporous apomictic plants. The F1 progenies were classified through a visual progeny test carried out on few F2 plants. The number of sexual F1s highly exceeded the apomictics leading to the conclusion that apomixis was controlled by a few recessive genes. The present study examines the inheritance of apospory in bahiagrass. A sexual plant was self-pollinated and crossed with an aposporous apomictic plant as pollen donor. Backcross and F2 progenies were obtained in several combinations. All self-pollinated sexual plants or sexual x sexual crosses produced progenies free of apospory. All crosses involving a sexual and an apomictic plant produced approximately three times more apospory-free plants than plants with apospory. Bahiagrass is of autotetraploid origin and hence is expected to display tetrasomic inheritance. The most widely accepted genetic model for inheritance of apospory in tropical grasses is a single dominant gene with tetrasomic inheritance. In the present experiments none of the apospory-free F1s segregated for the apospory trait indicating that it is most likely a dominant character. However, the observed results fit better a modified model: tetrasomic inheritance of a single dominant gene with pleiotropic effect and incomplete penetrance. The excess of apospory-free plants in the F1 progeny could be ascribed to some distortion in the segregation pattern due to a pleiotropic lethal effect of the dominant A allele with incomplete penetrance. Alternatively, partial lethality of factors linked to aposporous gene may account for segregation distortion against apospory.

Determination of the mode of reproduction of bahiagrass hybrids using cytoembryological analysis and molecular markers

“…The ratio of 1:2.6 (sexual plants:apomictic) was found; however, in studies conducted at IBONE, evaluating 44 hybrids, Martínez et al (2001) found a ratio of 4.5:1 (sexual:apomictic). This distorted segregation is possibly related to the lethal effect of the dominant pleiotropic locus or partial lethality factors linked to the aposporic gene.…”

“…Contrary to that found in this study, Fortes et al (2004) mentioned that this distortion had been found responsible for values of 4.3:1 (sexual:apomictic), differing from the expected 1:1. Martínez et al (2001) found values of 2.8:1 (sexual: apomictic), while the work of Stein et al (2004) found 6.5:1 (sexual:apomictic). All these studies were conducted with Paspalum notatum genotypes.…”

“…The genetic aposporic segregation was previously explained by a genetic model of simple Mendelian inheritance with dominance of apospory over sexual reproduction, but with a strong distortion of segregation (Martínez et al, 2001). Contrary to that found in this study, Fortes et al (2004) mentioned that this distortion had been found responsible for values of 4.3:1 (sexual:apomictic), differing from the expected 1:1.…”

“…Thus, the sexual process can coexist with unreduced embryo sacs, becoming initially aposporic in one embryo sac (Karasawa, 2009) frequency of incidences of sexual and apomictic embryos (Koltunow, 1993). The genetic control of apomixis in tetraploid P. notatum is by a single dominant locus and with Mendelian segregation, but in controlling the expression of apomixis, there is probably a pleiotropic lethal effect of the dominant locus or partial lethality factors linked to the aposporic gene, possibly causing segregation distortion in favor of plants with the sexual mode of reproduction (Martínez et al, 2001). Valle and Savidan (1996) reported that the occurrence of two types of sacs in the same embryonic egg in apomictic plants of Brachiaria is considered indicative of facultative apomixis.…”

Sequence Analysis of Bacterial Artificial Chromosome Clones from the Apospory-Specific Genomic Region ofPennisetumandCenchrus

“…A single dominant ''locus'' is required for apomeiosis and parthenogenesis in the aposporous grasses Pennisetum/Cenchrus (Sherwood et al, 1994;OziasAkins et al, 1998), Brachiaria (Pessino et al, 1997), and Paspalum (Martinez et al, 2001) and in the diplosporous grass Tripsacum (Grimanelli et al, 1998). In all cases, penetrance of the trait varied among the apomictic siblings.…”