<b>Repeatability, number of harvests, and phenotypic stability of dry matter yield and quality traits of Panicum maximum jacq.

Abstract

ABSTRACT. Selection of superior forage genotypes is based on agronomic traits assayed in repeated measures. The questions are how repeatable the performance of individual genotypes is and how many harvests are needed to select the best genotypes. The objectives were to estimate repeatability coefficients of dry matter yield (DMY) and forage quality, their phenotypic stability and the number of harvests needed for an accurate selection. Two randomized complete block design experiments data with 24 genotypes each, undergoing 12 and 16 harvests, over a period of 2 and 3 years, respectively, were used. The DMY repeatability estimates ranged from 0.42 to 0.55, suggesting a low heritability. The mean numbers of repeated measures were 5 and 7 harvests for 0.80 and 0.85 accuracy, respectively. The inclusion of the first two harvests negatively affects the estimates. Repeatability for quality traits ranged from 0.30 to 0.69, indicating low to moderate heritability.Keywords: repeated measures, selection efficiency, selection effectiveness.Repetibilidade, número de colheitas e estabilidade fenotípica da produção de matérica seca e de características de qualidade de Panicum maximum jacq. RESUMO.A seleção de genótipos superiores em forrageiras é feita para características agronômicas analisadas em medições repetidas no tempo. As questões estão relacionadas à repetibilidade do desempenho dos genótipos e ao número necessário de colheitas para selecionar aqueles superiores. Os objetivos foram estimar coeficientes de repetibilidade da produção de matéria seca (PMS) e de características de qualidade da forragem, a estabilidade fenotípica e o número de colheitas necessárias para uma seleção mais precisa. Dois experimentos em blocos casualizados com 24 genótipos cada um, submetidos a 12 e 16 colheitas, durante um período de dois e três anos, respectivamente, foram utilizados para o estudo. As estimativas de repetibilidade de PMS variaram de 0,42 a 0,55, sugerindo baixa herdabilidade. Os números de colheitas foram cinco e sete para 0,80 e 0,85 de acurácia, respectivamente. A inclusão das duas primeiras colheitas afeta negativamente as estimativas de PMS. A repetibilidade para as características de qualidade variou de 0,30 a 0,69, indicando baixa à moderada herdabilidade.Palavras-chave: medidas repetidas, eficiência de seleção, eficácia de seleção.

High-Resolution Linkage Map With Allele Dosage Allows the Identification of Regions Governing Complex Traits and Apospory in Guinea Grass (Megathyrsus maximus)

“…The heritability of the nutritional traits varied from low (0.06), obtained for SIL_S, to moderate (0.32), obtained for OM_L. This result also reinforces the necessity of more harvests for the efficient selection of superior genotypes for nutritional traits (Fernandes et al, 2017). Traits IVD_L and IVD_S presented the same standard as the crude protein, with the H² of the stem being higher than that of the leaf (Table 1).…”

“…In a selection study of U. decumbens and U. humidicola, Figueiredo et al (2019) identified a significant Genotype x Harvest Interaction (GHI) effect (p<0.05) for different agronomic and nutritional traits, which reflect differences in the relative performances of genotypes across harvests. GHI also has been reported as significant in M. maximus, and the average number of harvests needed for a reliable selection of nutritional traits, such as OM and CP, would be 3 and 5 at accuracy levels of 0.80 and 0.85, respectively (Fernandes et al, 2017). Thus, GHI directly affects the selection of the genotypes and further studies with more harvests are needed to consolidate our results about putative QTLs to nutritional traits.…”

“…The selection of a superior genotype of perennial tropical forages is based on the analysis of traits through repeated measures over a number of harvests, seasons, and years (Fernandes et al, 2017). The nutritional QTLs found in our study need further investigation because only one harvest was analyzed and interactions could not be measured.…”

Repeatability and genotypic stability of agronomic characteristics in Panicum maximum Jacq.

“…According to the authors, in general, variations in the estimate of the repeatability coefficient indicate the need to use the several methods available to obtain an accurate range within which, more likely, the actual value for this parameter is found. The same response was also observed by Cargnelutti Filho et al (2004), Braz et al (2015b) and Fernandes et al (2017) in P. maximum. Braz et al (2015b) highlighted a large discrepancy between methods, which was attributed to the bias of the principal component analysis methods when the actual value of the coefficient approaches zero (Mansour et al, 1981).…”

“…These results indicate that TDM evaluation requires a smaller number of repeated measures for a good level of reliability in the prediction of the response and identification of superior genotypes. Fernandes et al (2017), estimating repeatability coefficients of TDM production in 24 genotypes of P. maximum, in 12 harvests, observed values varying from 0.259 to 0.413, by the ANOVA and PCCOV methods, respectively. This amplitude was greater than that observed in this paper.…”