Understanding leaf generation dynamics, their seasonal changes, and their responses to nitrogen fertilization (NF) is key to improving pasture utilization efficiency. The objectives of this research were to determine structural and morphogenetic variables underlying changes in herbage mass on a set of Paspalum notatum genotypes. Ten P. notatum genotypes were evaluated in experimental plots following a completely randomized block design under a split-plot arrangement for two N-rates during four periods. Increased herbage mass (HM) after N-fertilization was explained by a higher tiller density (TD) (41.8%) and tiller weight (TW) (22.1%). The increment of TW after NF was due to the increase in leaf blade length (LBL) and width (LBW). During the flowering season, NF increases the reproductive tiller density by 262.5%. Seasonal variation in HM was mainly explained by changes in LBL that modified TW. Morphogenetic traits differed between genotypes of different growth habits; therefore, different management practices are suggested. The average increase in leaf elongation rate in response to NF was about 36.7%, generating longer leaves despite reductions in leaf elongation time (LET). The depletion in LBL and consequently in TW and HM during the autumn was attributed to the reduction in LET.

The genetic systems of Paspalum species have not been extensively studied. We analyzed the ploidy, reproductive mode, mating system, and fertility of four Paspalum species—Paspalum durifolium, Paspalum ionanthum, Paspalum regnellii, and Paspalum urvillei. An analysis of 378 individuals from 20 populations of northeastern Argentina was conducted. All populations of the four Paspalum species were pure tetraploid and had a sexual and stable reproductive mode. However, some populations of P. durifolium and P. ionanthum showed low levels of apospory. Populations of P. durifolium and P. ionanthum had low seed sets under self-pollination but were fertile under open pollination, showing that self-incompatibility likely caused self-sterility. In contrast, populations of P. regnellii or P. urvillei showed no evidence of apospory, and seed sets in both self- and open pollination conditions were high, suggesting that they are self-compatible due to the absence of pollen–pistil molecular incompatibility mechanisms. The evolutionary origin of the four Paspalum species could explain these differences. This study supplies valuable insights into the genetic systems of Paspalum species, which could have implications for their conservation and management.

The tetraploid germplasm of Paspalum contains a large diversity that can be used to generate better forages. The objective was to evaluate a group of Paspalum notatum and Paspalum simplex apomictic hybrids for a set of agronomic traits and apomixis expressivity. Forage yield, cold tolerance, winter regrowth, and seed yield were evaluated. The expressivity of apomixis was evaluated in P. simplex hybrids by flow cytometry. Progeny testing with molecular markers was used to determine the genotypic variability in the progeny. Differences within P. notatum and P. simplex hybrids were observed for all traits, and some of them were superior in comparison with the controls. The accumulated forage yield during three years was 988 g m⁻² in the P. notatum hybrids, whereas, in P. simplex, the average forage yield per harvest (40 days of regrowth) was 180 g m⁻². In P. simplex, the apomixis expressivity varied between 0 and 100%, and 65% of the hybrids showed high apomixis expressivity (superior to 70%). The genotypic mean homogeneity in the progeny was 76% and 85% in P. notatum and P. simplex, respectively. The generation of hybrids with high apomixis expressivity that combine good agronomic performance and homogeneity in the offspring is possible in tetraploid P. notatum and P. simplex.

Exploring the genetic diversity and reproductive strategies of Paspalum species is essential for advancing forage grass improvement. We compared morpho-phenological, molecular, and genotypic variation in five tetraploid Paspalum species with contrasting mating systems and reproductive modes. Contrary to previous findings, selfing (Paspalum regnellii and P. urvillei) and outcrossing (P. durifolium and P. ionanthum) species exhibited similar phenotypic diversity patterns, with low intrapopulation variability and no morphological differentiation among populations. The apomictic species (P. intermedium) exhibited low intrapopulation phenotypic variation but high population differentiation, indicative of genetic drift and local adaptation. Outcrossing species showed greater intrapopulation genotypic variation than selfing species, which displayed a high population structure due to restricted pollen migration. The apomictic species exhibited the lowest intrapopulation molecular diversity, forming uniclonal populations with high interpopulation differentiation, highlighting the fixation of distinct gene pools via apomixis. This is the first report about genetic diversity in populations of sexual allopolyploid species of Paspalum. Population structure in these allotetraploid Paspalum species is primarily shaped by how reproductive modes, mating systems, and geographic distribution influence gene flow via pollen and seeds. Our findings contribute significantly to the conservation and genetic improvement of forage grasses, particularly for developing cultivars with enhanced adaptability and productivity.