Estratégias para depleção do banco de sementes de azevém do solo

Abstract

The ryegrass (Lolium multiflorum Lam.), is one of the main weed species in regions of temperate and subtropical climate. The highly competitive nature, genetic variability, longevity and expressive seed production favor its rapid geographical expansion, as well as increasingly problematic infestations of winter cereal fields. Ryegrass seeds are often dormant and, when disseminated, can germinate gradually in the growing season. Weed persistence is dependent on the soil seed bank, so its depletion can be an excellent management strategy before weed species start to affect economic culture. Thus, the study aimed to evaluate practices for reducing seed return and the amount of ryegrass seeds present in the soil seed bank, in addition to knowing the dynamics of the ryegrass seed bank in the field. Therefore, three studies were carried out. The first aimed to evaluate the production and the physiological quality of ryegrass seeds, in response to the application of herbicides and plant growth regulators, in three stages of plant development. In the second study, the aim was to characterize the dynamics of the seed bank of two biotypes of L. multiflorum, one resistant and the other sensitive to glyphosate, under no-tillage system. Finally, the third experiment aimed to evaluate the performance of plant growth regulators and their interaction with potassium nitrate (KNO3), in inducing or releasing dormancy and germinating seeds of sensitive and glyphosate-resistant ryegrass biotypes. The production of ryegrass seeds has been reduced by up to 100% and this result is dependent on the product, dose and stage of the plant in which it is applied. In the field, ryegrass distributes germination over time and this behavior is equivalent in a sensitive and glyphosate resistant biotype. ABA and paclobutrazol inhibit the germination of ryegrass seeds and fluridone stimulates it, but the resulting seedlings are unable to continue their development by tissue bleaching. KNO3 stimulates germination in most cases and partially cancels the inhibitory effects of ABA. In conclusion, this research provides information on practices for reducing the quantity and replacement of ryegrass seeds in the soil seed bank, which can be implemented to prevent ryegrass competition with crops and the spread of ryegrass resistance to herbicides. In addition, knowledge of the germinative behavior of the ryegrass seed bank in the soil can help predict the time of seedling emergence and carry out appropriate control measures.