RESUMO
Objetivou-se, neste trabalho, avaliar a variabilidade genética de alguns caracteres da planta e o desempenho agroindustrial em cultivares de cana-de-açúcar. O delineamento experimental foi o de blocos casualizados, com quatro blocos e dezesseis cultivares. As parcelas foram formadas por cinco sulcos de 8,0 m de comprimento, espaçados de 1,0 m, caracterizando uma área útil de 40 m². Foram avaliadas as variáveis toneladas de cana por hectare (TCH), toneladas de pol por hectare (TPH), pol na cana (PC), fibra por cento cana (FIB), brix na cana (BC) e pureza na cana (PUR). O TCH é o componente mais influenciado pelos ciclos de colheita da lavoura de cana-de-açúcar e o menos expressivo para os demais caracteres estudados. As variáveis TCH e TPH refletiram a maior parte da variação fenotípica observada devida às causas genéticas, indicando êxito na seleção no melhoramento desses caracteres. Os genótipos SP78-4764, SP86-0621 e SP86-127 demonstraram potencial produtivo do ponto de vista agroindustrial. O efeito de ciclo de colheita da cana foi altamente significativo indicando o comportamento específico entre as cultivares durante os cortes da cana.
The aim of this work was to evaluate the genetic variability of some characters of the plant and the agroindustrial performance of sugar cane cultivars. The experimental design was the complete randomized blocks with four replications and 16 cultivars, being four of them used as check varieties. The plots were formed by five furrows of 8.0 m length, spaced 1.0 m, characterizing a useful area of 40 m². The variables evaluated were the tons of cane per hectare (TCH), tons of pol per hectare (TPH), pol in the cane (PC), percent cane fiber (FIB), brix in the cane (BC) and purity in the cane (PUR). The TCH is the component most influenced by the harvest cycles of the sugar cane farming and the least expressive for the other studied characters. The variables TCH and TPH reflected most of the phenotypic variation observed due to genetic causes, indicating success in the selection for the improvement of these characters. The genotypes SP78-4764, SP86-0621, and SP86-127 demonstrated productive potential from the agroindustrial point of view. The effect of the cane cut cycle was highly significant, indicating specific behaviors among the cultivars during the cane harvest.
RESUMO
We used deterministic simulation of four alternative multiple ovulation and embryo manipulation (MOET) closed nucleus schemes to investigate the benefits of using marker-assisted selection (MAS) of Nellore (Bos indicus) beef cattle embryos prior to transplantation to reduce the age at first calving (AFC). We found that MAS resulted in increased genetic gain as compared to selection without AFC quantitative trait loci (AFC-QTL) information. With single-stage selection the genetic response (GR) increased as follows: GR = 0.68 percent when the AFC-QTL explained 0.02 of the AFC additive genetic variance (sigma2A); GR = 1.76 percent for AFC-QTL explaining 0.05 sigma2A; GR = 3.7 percent for AFC-QTL explaining 0.1 sigma2A; and GR = 55.76 percent for AFC-QTL explaining 0.95 sigma2A. At the same total selected proportion, two-stage selection resulted in less genetic gain than single stage MAS at two-years of age. A single stage selection responses of > 95 percent occurred with pre-selected proportions of 0.4 (0.1 sigma2A explained by AFC-QTL), 0.2 (0.3 sigma2A explained by AFC-QTL) and 0.1 (0.5 sigma2A explained by AFC-QTL), indicating that the combined use of MAS and pre-selection can substantially reduce the cost of keeping recipient heifers in MOET breeding schemes. When the number of recipients was kept constant, the benefit of increasing embryo production was greater for the QTL explaining a higher proportion of the additive genetic variance. However this advantage had a diminishing return especially for QTL explaining a small proportion of the additive genetic variance. Thus, marker assisted selection of embryos can be used to achieve increased genetic gain or a similar genetic response at reduced expense by decreasing the number of recipient cows and number of offspring raised to two-years of age.