Optimizing breeding strategies in ruzigrass: shading effect and experimental planning

Abstract

Brazilian livestock farming is predominantly conducted on pastures, highlighting the importance of genetic breeding of forage species such as Urochloa ruziziensis. This species is a promising alternative for obtaining productive cultivars with high nutritional quality, adapted to integrated crop-livestock systems (ICLS). Increasing the efficiency of the U. ruziziensis breeding program depends on information that allows the optimization of available resources, such as plot size, the optimal number of replications and harvests, and the use of indirect selection for target environments, such as ICLS. Based on the above, the objectives of this study were to evaluate the performance of U. ruziziensis clones under full sun and 50% shading and verify the efficiency of indirect selection for shade tolerance; define the optimized number of replications and harvests in single-plant plot (SPP) trials; and compare the performance of clones under two types of plots: a single-plant plot and a plot formed from eight plants (SWARD). Greenhouse trials were conducted in Juiz de Fora, MG to evaluate U. ruziziensis clones under full sunlight and 50% shading. Additionally, two field experiments were conducted in Lavras, MG, one with single-plant plots (SPP) with 24 replications and another with eight plants forming a sward (SWARD) with three replications. Plant height (PH - cm), vigor scores (VS - score), fresh mass yield (FMY - g plot-1

), and regrowth capacity (RC - score) were evaluated. Data were analyzed using R software, and parameters such as variance components, accuracy, heritability, Spearman correlation, coincidence index, and relative genetic gain were estimated. It was concluded that indirect selection of U. ruziziensis clones for shading conditions based on full sun evaluation is feasible. To achieve high reliability in selection in SPP trials, at least five replications are recommended for evaluating PH, RC, and VS traits, and 10 replications for FMY. The minimum number of harvests needed to achieve high selective coincidence was five for the evaluated traits. The relative performance of the clones was not coincident in the SPP and SWARD trials. The efficiency of indirect selection of U. ruziziensis clones for larger plots based on single-plant plots was more pronounced for VS and RC traits.