Elephant grass is a plant of tropical origin with high biomass-production potential that stands out today as an alternative energy source. The potential of its genotypes depends on the genotype × environment interaction. The objective of this study was to estimate the genotype × environment interaction and compare stability methods in elephant grass for biomass production in a biannual cutting regime. The experiment was conducted in a randomized block design with two replicates and evaluations of 73 elephant-grass genotypes in six cuts. The trait dry matter yield was utilized for the analysis of the genotype × environment interaction and the stability. The stability analysis methods employed were those of Yates and Cochran, Plaisted and Peterson, Wricke, Annicchiarico, Lin and Binns, and Huehn. Kang and Phan's ranking was adopted for all the methods. Spearman's coefficient was utilized to evaluate the degree of agreement between the different methods employed. Significant differences were observed for the genotype × environment interaction. Non-parametric Lin and Binns' and Annicchiarico's methods were more discriminating than the analysis of variance methods in the evaluation of stability and productivity of the tested genotypes.

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ABSTRACT. Elephant grass is a tropical forage plant widely distributed throughout Brazil. It was first exclusively used in the livestock sector as cattle feed. The grass is characterized by its high productivity and photosynthetic capacity and is considered as an alternative source of renewable energy. Here, we estimated the general combining ability of the parents and specific combining ability of the hybrids based on morpho-agronomic biomass-quality traits. The experiment was conducted in a randomized block design with 3 replicates. The diallel was composed of 16 hybrids and 2 groups of genitors. In the diallel analysis of variance, we observed a significant difference among treatments. A significant difference was observed among genitors for dry matter production (DMP). For the general combining ability of group 1, the traits leaf blade width, DMP, height, percentage of neutral detergent fiber, percentage of hemicellulose, percentage of lignin, percentage of acid detergent fiber, and percentage of cellulose were significant. For the estimates of general combining ability of DMP, parents Porto Rico

In forage-plants breeding, the selection of superior genotypes has been undertaken through successive harvests in previously established intervals. However, this process involves many steps, the evaluation of many traits, and a great spending with costs and labor. Thus the estimate of the repeatability is essential in improvement of perennials, it allows predicting genotypic value of the individual, the minimum number of evaluations in the selection of genotypes and minimizes resources and time in the selection of promising individuals. The objective of this study was to estimate the repeatability coefficient for morphological traits in elephant grass and determine the number of evaluations needed for phenotypic selection more efficient. The experimental randomized block design with 53 genotypes and two replications. The repeatability coefficients were estimated for variables plant height, number of tillers, stem diameter and dry matter yield, using the methods of Anova, Principal Components and Structural Analysis. We observed significant differences between genotypes (P <0.01) for all variables. The main components provide larger estimates of repeatability when compared to other methods. Estimates of the repeatability coefficients are of high magnitude average for the variables plant height (0.44) number of tillers (0.44) and stem diameter (0.63) and low magnitude for dry matter production (0.27). The Principal Components method requires five, five, two and eleven measurements for plant height, number of tillers, stem diameter and dry matter yield, respectively, with 80% reliability.

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