Dialelo completo e associação entre caracteres de rendimento em trigo (Triticum aestivum L.)

Abstract

The aim of this work was to evaluate the combining ability of a wheat F2 generation through a full diallel, as a criterion for selecting promising genitors, as well as to reveal the associations of cause and effect between components and grain yield as function of different nitrogen management. Two experiments were carried out in the experimental field of the Federal University of Santa Maria, Campus Frederico Westphalen. Five wheat genotypes (Tbio Mestre, Mirante, Quartzo, Pampeano e Fundacep Horizonte) were used in the first experiment, which were subjected to artificial crosses in the year of 2013, according to the full diallel model. In 2015, the twenty F2 populations and the five genitors were conducted in Federer´s augmented blocks, with genitors arranged in four repetitions. The evaluated traits were: mass of grains per plant, spike insertion height, plant height, number of fertile tillers, spikelets spacing in the spike, number of spikelets and spike length. There were performed the analyses of general and specific combining ability, maternal and non-maternal reciprocal effects. The second experiment was conducted in randomized blocks, under subdivided plots, with three genotypes (Fundacep 52, TBIO Mestre and TBIO Itaipu), two nitrogen sources (urea and ammonium nitrate) and four nitrogen managements (I: absence of nitrogen, II: 100% at tilling stage, III: 50% at tilling stage, and 50% at booting stage, VI: 33.3% at tilling, 33.3% at booting and 33.3% at flowering. The evaluated traits were: mass of a thousand grains, number of grains per spike, mass of grains in the main spike, grain yield, plant height, number of fertile tillers and spike length. It was performed the analysis of joint variance followed by Pearson´s linear correlation and individual path analysis for each nitrogen management. The genitor Cep Horizonte presents high combining ability for mass of grains per plant. Quartzo and Mirante maximized the number of spikelets per spike and spike length, respectively, and Tbio Mestre presented itself promising for reduction of spike insertion height, plant height and spikelet spacing in the spike. Regarding the crosses performed, there are favorable hybrid combinations for at least one of the evaluated traits based on the specific combining ability. The reciprocal effect is present in the evaluated traits. Nitrogen management alters the relation of cause and effect among grain yield and its components. The adoption of no nitrogen on topdressing (management I) indicates the cause and effect relationship between number of fertile tillers and grain yield of wheat. The adoption of any other nitrogen managements reveals that mass of grains in the main spike and number of fertile tillers present cause and effect relationship with grain yield.