In warm‐temperate regions, the adoption of warm‐season forage grasses has been hindered by low and unpredictable seedling emergence because of seed dormancy. Developing models driven by temperature (T) and soil water potential (Ψ) may provide tools for choosing adequate sowing conditions. Models are usually developed with controlled chamber germination data, but they can be built using field emergence and weather station data. Seedling emergence data of four Paspalum populations (two dallisgrass subspecies, bahiagrass and vaseygrass) were gathered from five experiments in three Campos locations (Buenos Aires, Montevideo and Salto) during two years, with fall and spring sowing dates and irrigated and non‐irrigated plots. Thermal and hydrothermal time models were used for emergence timing. The predictions were better for irrigated plots and fall sowings. For maximum emergence proportion (MEP), a mixed linear model was adjusted. Within a non‐irrigated treatment, the higher MEP was for early‐spring sowings, but the lowest for late‐spring ones. Additionally, a thermal time index (TTI) was modified to model MEP. A coefficient which weighs degree‐days accumulation according to the hydrothermal range (HTR) of each day was set. The HTRs were defined by T and Ψ thresholds. Thresholds and coefficient values were optimized by genotype until linear regressions between MEP and modified TTI achieved higher fit. Days with high temperature (>18°C or 20°C according to genotype) accumulated half or none of degree‐days when high‐ or mid‐soil water content was available, respectively. Differences among Paspalum genotypes, sowing date recommendations and modified TTI usefulness were discussed.
Melilotus albus is recognised as an important source of forage for ruminant animals in rangelands, particularly some of the germplasm of Melilotus collected in Argentina. This study was designed to evaluate the effects of 2 years of selection in M. albus for late flowering and branching on forage yield in a 2-year field plot experiment and to evaluate the effects of selection for late flowering on photoperiodic requirements in a 1-year pot experiment under natural and artificial lighting conditions. Three populations were evaluated, namely original population (T), a population selected for late flowering and greater number of basal branches (ET1), and a population selected only for late-flowering plants (ET2). The field plot experiment showed that total DM yield per year was higher for ET1 and T than for ET2 in Year 1 and higher for ET1 than T and ET2 in Year 2. Relative leaf yield was higher for ET1 and ET2 than for T in both years. Leaf number was greater for ET1 than for ET2 and T in both years. The number of new basal and total branches was greater in ET1 than in ET2 and T for both years. The pot experiment showed that days to flowering, calculated as the average of natural and artificial lighting treatments, were higher in ET2 and ET1 (83.4 days ± 15 and 72.8 days ± 19, respectively), than in T (61.2 days ± 21). Supplementary lighting reduced days to flowering compared with natural lighting conditions for all populations (58.7 days ± 13 v. 86.1 days ± 12). Results showed that 2 years of selection proved to be efficient in breeding for late flowering and greater number of basal branches in M. albus. The longer vegetative stage observed in the improved populations can be explained by the selection of plants which require a longer photoperiod to flower. Selection for late flowering and greater number of basal branches resulted in a population with more leaves and higher relative leaf yield.
Paspalum dilatatum (common name dallisgrass), a productive C4 grass native to South America, is an important pasture grass found throughout the temperate warm regions of the world. It is characterized by its tolerance to frost and water stress and a higher forage quality than other C4 forage grasses. P. dilatatum includes tetraploid (2n = 40), sexual, and pentaploid (2n = 50) apomictic forms, but is predominantly cultivated in an apomictic monoculture, which implies a high risk that biotic and abiotic stresses could seriously affect the grass productivity. The obtention of reproducible and efficient protocols of regeneration and transformation are valuable tools to obtain genetic modified grasses with improved agronomics traits. In this review, we present the current regeneration and transformation methods of both apomictic and sexual cultivars of P. dilatatum, discuss their strengths and limitations, and focus on the perspectives of genetic modification for producing new generation of forages. The advances in this area of research lead us to consider Paspalum dilatatum as a model species for the molecular improvement of C4 perennial forage species.
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