Lignina no tegumento de semente de soja: deterioração por umidade e dano mecânico e tamanho de amostra para o teste de tetrazólio

Abstract

Soybeans are the main oilseed grown in the world, and among the factors that hinder the production of high-quality soybeans, is the frequent rainfall during periods of maturation and preharvest. Characteristics of seeds as the seed coat lignin content may reflect a greater or lesser susceptibility to deterioration from humidity and mechanical damage. Thus, although there are data and evidence that the lignin content confers resistance to deterioration from humidity, there is a lack of experiments with methods which are similar to the adverse weather conditions that the seeds remain exposed in the field. Therefore, this study was developed in order to evaluate the relationship between the lignin content of soybean seed coat, with tolerance to deterioration from humidity and mechanical damage. The work primarily consists of a brief literature review, Chapter I, and two more chapters. Chapter II contains the work that evaluates the relationship between seed coat lignin content of soybean seeds with tolerance to deterioration from humidity and mechanical damage. Chapter III, to qualify the experiments in the area, is aimed to estimate the ideal sample size, in number of seeds required for the tetrazolium test for soybean seeds. The CD 208 and CD 215 cultivars, with higher lignin content in seed coat, 4.19% and 2.64%, respectively, had higher vigor after stress with simulated rainfall. Furthermore, the cultivar CD 208, was also less susceptible to damage from humidity and mechanical damage. Oxidative stress in shoots and roots of the seedlings was demonstrated by the enzyme peroxidase activity Guaiacol, which increased the cultivars CD 215, CD 202 and BRS 184, with lower lignin content in seed coat than 3%. About the seeds, the cultivar BRS 184 with lower lignin content, 1.69%, showed a higher oxidative stress due to increased activity of the enzyme Guaiacol Peroxidase and lipid peroxidation. The sample size in number of seeds, to assess humidity damage through the tetrazolium test in soybean seeds is dependent on the physiological quality of cultivars, recommending to the highest level of precision 200 seeds per lot, and for a below level and acceptable accuracy, 0.5% CI, 121 seeds.