Single-plant selection at ultra-low density to improve stability of a bread wheat cultivar

The goal of the study was to assess within bread wheat (Triticum aestivum L.) cultivar variation through honeycomb selection, under the ultra-low density (ULD) of 1.2 plants/m(2). Divergent selection of individual plants characterized as providing high (H) and low (L) yield led to 10 H and 10 L first generation families, respectively. Further selection of high yielding plants within H families resulted in 20 second generation families. Progeny evaluation was conducted in two locations, under ULD and the typical crop density (TCD) of 500 plants/m(2). Six of the first generation families were also tested, in two locations for two years, across four densities (100, 300, 500, and 700 plants/m(2)). Intra-cultivar selection improved yield potential per plant (i.e., expressed under low competition conditions), and there was an indication of overall crop yield potential improvement (i.e., maximum yield per unit area). Compared to the original cultivar at ULD conditions, five of the H first generation and 15 of the second generation families had significantly higher grain yield per plant (by 18 to 53%). Two of the H first generation and four of the second generation families significantly outperformed the original cultivar by 17 to 22% under TCD. Experimentation across the four densities showed that derived families exhibited less density dependence than their original cultivar, a determinant parameter for stability of performance. Results constituted evidence of low densities being more suitable for breeder's seed maintenance, so that any existing or newly developed variation is beneficially exploited.