Physiological and genetic implications to consider in tetraploid bahiagrass breeding

Bahiagrass, Paspalum notatum Flüggé, is a warm-season, perennial grass extensively cultivated as forage and utility turf in southeastern USA. The tetraploid germplasm of this species constitutes an underexploited source of genetic variation. This variation has great potential for bahiagrass improvement because of the possibility of fixing superior hybrids by manipulating apomixis. Physiological and genetic variables that might have a major impact on the process of improving this species were studied. The objectives of this research were to evaluate the transmission of apomixis through generations, and estimate the genetic variability for growth habit, cool-season growth, and freeze resistance resulting from hybridization of sexual and apomictic F₁ clones. Additionally, estimates were made on the seasonal biomass yields and nitrogen and phosphorus accumulation and the genetic variability for the rate of root depth development, root mass and root length density among these novel F₁ hybrids. The relationship between root development and nitrogen uptake from deep soil layers, and the relationship between biomass yields and root characteristics were also determined.;Approximately 20% of the F₁ and F₂ were classified as apomictic. Eleven percent of the F₁₁ but only 3% of the F₂ were classified as highly apomictic. This variable expressivity might be caused by the genetic background or epigenetic variation. The genetic variation observed for growth habit, cool-season growth, and freeze resistance remained relatively constant between the F₁ and F₂. Apomicitc F₁ hybrids accumulated more nitrogen and phosphorus in spring and produced higher cool-season and annual biomass yields compared to common bahiagrass cultivars. Little genetic variation was observed for nitrogen and phosphorus concentrations in foliage among these hybrids. Genetic variation for rate of root depth development was observed among hybrids. Higher rates of root depth development resulted in faster access and uptake of nitrogen, and higher root and shoot mass. Variation for root length density was found among apomictic hybrids during the second growing season. No relationship was found between root length density or root mass, and above-ground biomass production. The fertilization rate did not affect root mass or root length density. Root activity might play an important role in nutrient uptake and biomass production.