Exigência térmica e fotoperiódica de cultivares de soja em função do grupo de maturação

Abstract

Soybean is a thermo-photoperiodic plant, in which the transition from one development stage to the other occurs as a function of temperature, and floral induction occurs as a result of the photoperiod, being considered a kind of short days. Both factors can have different responses between cultivars, which allows advancing studies to improve the positioning of materials in the field. The aim of the work was to evaluate whether soybean cultivars belonging to close maturation groups have similar requirements, in relation to the photoperiod, for flowering, and to the thermal sum, for the transition between stages and the total cycle. The experiment was conducted at the Experimental Station of the Universidade Tecnológica Federal do Paraná, Câmpus Dois Vizinhos, in the 2017/18 and 2018/19 crop seasons. Thirty-six cultivars, sown in mid-October, were evaluated for the accumulation of heat units between the Emergence (VE) stages - beginning of flowering (R1), R1- beginning of pod formation (R3), R3 – noticeable grain to touch (R5), R5 - physiological maturity (R7) and R7 - harvest maturation (R8). The photoperiod was determined at the stage of R1 of the cultivars. Yield components and grain yield were also evaluated. The experimental design used was randomized blocks (DBA), with three replicates. The data were submitted to analysis of variance, and then to Pearson's correlation. Larger GMR soybean cultivars accumulate more heat units to complete their cycle. Soybean cultivars that have greater heat accumulation in the vegetative phase, flower later, with no relationship between this characteristic and the GMR of the cultivars.