Variabilidade para o momento de máximo acúmulo de matéria seca de grãos entre linhagens de feijoeiro do tipo carioca

Abstract

Grain productivity of a plant depends, in the last instance, on the accumulation of dry matter in the grain. This accumulation is higher when nearing physiological maturation. Given the importance of this information, this work was conducted with the objective of verifying if variability occurs between the lines of the Carioca group of beans, relative to the accumulation rate of grain dry matter at the end of the cycle. The implications of this rate in the anticipated harvest of the culture, which occurs with certain frequency, were also verified. For this, experiments were conducted with three harvests during the periods from July of 2016 to May of 2017, in the Center for Scientific and Technological Development of the Universidade Federal de Lavras, Minas Gerais, Brazil. Sixteen lines of the Carioca-type bean were evaluated in a randomized blocks design, with five replicates. Four lines of four meters each constituted a plot. Using one of the lines in a plot, five plants were continuously collected from 26 to 35 days after blooming (DAB), depending on the harvest. Sampling was repeated at intervals of 2 to 4 days until harvest. Grain dry matter (DM) was obtained at each sampling time. With the data of DM per grain, the maximum accumulation of dry matter was estimated as indicator of physiological maturation, and, subsequently, the percentage of accumulated dry matter per day in relation to the maximum obtained. Variability was observed during the period of dry matter accumulation in the grain, however, it was of small magnitude between the evaluated bean lines, discouraging the specific selection of this trait. It was proven that the ideal moment for harvest is when 100% of the grain present streaks typical of the Carioca bean. However, the occurrence of streaks ranges between the pods of a plant, and even between grains of a same pod. The reduction of dry matter accumulated in the grain and, consequently, in productivity in relation to the maximum of dry matter accumulation is, in average, of 2.75% per day, that is, each day of harvest anticipation before reaching total physiological maturation, grain productivity is reduced in 2.75% per day.