Variabilidad inter poblacional en características asociadas a la capacidad de resiembra natural de raigrás: producción de semillas y dormancia

The study of variability in the viability and dormancy of ryegrass seeds (Lolium multiflorum var. Lam) would allow to know which genotype is best suited to different production systems. Ryegrass is an annual winter grass being one of the main species used for animal feed during the winter. It is chosen for its high forage production and good natural reseeding. Cultivars may have differences in traits associated with reseeding ability, including seed production and seed persistence in the soil. The seed persistence is achieved by maintaining dormancy and viability through summer. There are no previous reports in our country about cultivar differences regarding these traits, but regional and foreign information indicate that seed viability decreases with time lasting no more than two years in the soil, while dormancy disappears after 150 days of dispersion. The objective of this work was to evaluate the genetic variability in ryegrass in seed production, viability and dormancy in dry storage conditions and in the field. The effect of ploidy level was considered as a possible additional factor in variations of the parameters studied. The methodology consisted in the evaluation of seed production of 9 varieties of ryegrass (4 diploids and 5 tetraploids), estimating the seed yield components to know which was the best predictor of yield. The harvested seeds were used for two experiments, one was germination at 25ºC and 30ºC to evaluate dormancy and viability in three dry storage times (0, 39 and 67 days). In the other experiment the seeds of two contrasting genotypes (E284 and INIA Camaro) were buried in the soil to measure field germination, dormancy and viability every 30 days for approximately three months. There were differences between the genotypes for seed production, the most prominent being LExp2, Cambará and E284, with the number of seeds per spike being the characteristic best associated with seed production. As for the dormancy in dry storage there were differential behaviors in the dormancy and its evolution over time, allowing to group cultivars that quickly descend the dormancy within a month (p.j, E284) and others that took more time to descent (p.j, Bakarat) after two months. In the field there were differences in behavior, with interesting interactions observed, in which INIA Camaro maintained seed viability and seeds ready to germinate for a longer time than E284, showing a better persistence of the seed bank in the conditions of this experiment. Finally, it is concluded that there are differences in characteristics associated with the ability to reestablish and that these differences are better explained by the variation between cultivars than between ploidy levels and that there may be a group of cultivars that are better adapted than others to systems that include natural reseeding, depending on the environment and the management that is carried out. It is noteworthy that this species does not generate a persistent seed bank in the soil since the seeds at the end of the experiment, either germinated or lost viability.