Resistance mechanisms of sugarcane cultivars to spittlebug Mahanarva fimbriolata

The spittlebug Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) is one of the most important pests of sugarcane in Brazil. Measures for population control are currently restricted to the use of chemical insecticides and fungus Metarhizium anisopliae, in part because very little information exists regarding resistance of sugarcane cultivars. Therefore, the aim of this study was to evaluate resistance mechanisms of 12 different sugarcane cultivars to M. fimbriolata to provide information for growers for pest management. Isolated buds of each cultivar were planted in pots and kept in a greenhouse for approximately three months. The pots were then moved to climate test chambers (26 ± 1 ºC; 70 ± 10 % relative humidity; 12 h photoperiod) to carry out laboratory tests to evaluate adult feeding and female oviposition preferences (using both free-choice and no-choice tests) as well as the effects of cultivars on nymph development and cultivars tolerance to pest attack. The least attractive cultivars for adult feeding were IACSP96-2042 and IAC91-1099. Cultivars IACSP96-2042, IACSP96-3060 and IACSP94-2101 received the fewest eggs in the free-choice and no-choice oviposition tests and exhibited some level of antixenosis resistance. Cultivar IAC91-1099 showed the highest level of antibiosis resistance with a nymph survival rate in the roots of only 20 %. Finally, cultivar IACSP94-2094 appears to be tolerant to M. fimbriolata, as it did not show significant reductions in aboveground biomass weight, despite showing reduced leaf chlorophyll levels following pest attack.

Resistance mechanisms of sugarcane cultivars to spittlebug Mahanarva fimbriolata

The spittlebug Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) is one of the most important pests of sugarcane in Brazil. Measures for population control are currently restricted to the use of chemical insecticides and fungus Metarhizium anisopliae, in part because very little information exists regarding resistance of sugarcane cultivars. Therefore, the aim of this study was to evaluate resistance mechanisms of 12 different sugarcane cultivars to M. fimbriolata to provide information for growers for pest management. Isolated buds of each cultivar were planted in pots and kept in a greenhouse for approximately three months. The pots were then moved to climate test chambers (26 ± 1 ºC; 70 ± 10 % relative humidity; 12 h photoperiod) to carry out laboratory tests to evaluate adult feeding and female oviposition preferences (using both free-choice and no-choice tests) as well as the effects of cultivars on nymph development and cultivars tolerance to pest attack. The least attractive cultivars for adult feeding were IACSP96-2042 and IAC91-1099. Cultivars IACSP96-2042, IACSP96-3060 and IACSP94-2101 received the fewest eggs in the free-choice and no-choice oviposition tests and exhibited some level of antixenosis resistance. Cultivar IAC91-1099 showed the highest level of antibiosis resistance with a nymph survival rate in the roots of only 20 %. Finally, cultivar IACSP94-2094 appears to be tolerant to M. fimbriolata, as it did not show significant reductions in aboveground biomass weight, despite showing reduced leaf chlorophyll levels following pest attack.(AU)

Composição bromatológica e digestibilidade de cana-de-açúcar colhida em duas épocas do ano / Chemical composition and digestibility of sugarcane harvested at two periods of the year

Objetivou-se com este estudo avaliar o efeito da época de corte sobre a composição bromatológica e digestibilidade in vitro de genótipos de cana-de-açúcar, comparar a composição bromatológica e digestibilidade in vitro das frações colmo e folhas, e estabelecer possíveis correlações entre composição química e digestibilidade in vitro da planta inteira de genótipos da cana-de-açúcar. Nove genótipos foram colhidos em maio e setembro de 2006. Em maio, somente a fração planta inteira foi analisada, em setembro foram separados em colmos, folhas ou planta inteira para determinação da composição bromatológica, sacarose (POL) e digestibilidade in vitro. Colmos apresentaram menor teor de fibra em detergente neutro (FDN) e lignina na MS, e maior digestibilidade in vitro da matéria seca (DIVMS) do que folhas. Em contrapartida, apresentaram menor digestibilidade in vitro da FDN (DIVFDN), maior teor de lignina na FDN e menor concentração de proteína bruta (PB). Houve redução no teor e digestibilidade da FDN com o avanço da maturidade, enquanto que DIVMS, POL e lignina aumentaram. A DIVMS se mostrou negativamente correlacionada com FDN e FDN/POL, porém não houve correlação entre DIVFDN e FDN ou FDN/POL. Conclui-se que o avanço da maturidade promoveu redução na DIVFDN e aumento na DIVMS, não existindo correlação genética entre acúmulo de açúcar e digestibilidade in vitro da fibra. Os dados deste artigo indicam não ser esperado que a seleção de genótipos com maior DIVFDN do colmo altere o teor de açúcar do mesmo.(AU)

The objectives of this study were to evaluate the effect of time of harvest on chemical composition and in vitro digestibility of sugarcane genotypes, to compare chemical composition and in vitro digestibility of the stem and leaf fractions, and to determine possible correlations between chemical composition and in vitro digestibility of the whole plant in sugarcane genotypes. Nine genotypes were harvested in May and September of 2006. In May, only the whole-plant fraction was analyzed, in September the genotypes were separated in stems, leaves or whole-plant for determination of chemical composition, sucrose (POL) and in vitro digestibility. Stems had lower neutral detergent fiber (NDF) and lignin in the DM, and greater in vitro dry matter digestibility (IVDMD) than leaves. However, stems had lower in vitro NDF digestibility (IVNDFD), higher lignin in the NDF and lower crude protein (CP). The NDF and IVNDFD were reduced with advanced maturity, while IVDMD, POL and lignin were increased. IVDMD was negatively correlated with NDF and NDF/POL, however there was no correlation between IVFDND and NDF or NDF/POL. It can be concluded that with the advance in maturity the IVNDFD was reduced and IVDMD was increased, and there was no genetic correlation between accumulation of sugar and in vitro fiber digestibility. Data from this study indicate that it is not expected that selection of genotypes with greater stem IVNDFD would alter the sugar content of the plant.(AU)

Composição bromatológica e digestibilidade de cana-de-açúcar colhida em duas épocas do ano / Chemical composition and digestibility of sugarcane harvested at two periods of the year

Objetivou-se com este estudo avaliar o efeito da época de corte sobre a composição bromatológica e digestibilidade in vitro de genótipos de cana-de-açúcar, comparar a composição bromatológica e digestibilidade in vitro das frações colmo e folhas, e estabelecer possíveis correlações entre composição química e digestibilidade in vitro da planta inteira de genótipos da cana-de-açúcar. Nove genótipos foram colhidos em maio e setembro de 2006. Em maio, somente a fração planta inteira foi analisada, em setembro foram separados em colmos, folhas ou planta inteira para determinação da composição bromatológica, sacarose (POL) e digestibilidade in vitro. Colmos apresentaram menor teor de fibra em detergente neutro (FDN) e lignina na MS, e maior digestibilidade in vitro da matéria seca (DIVMS) do que folhas. Em contrapartida, apresentaram menor digestibilidade in vitro da FDN (DIVFDN), maior teor de lignina na FDN e menor concentração de proteína bruta (PB). Houve redução no teor e digestibilidade da FDN com o avanço da maturidade, enquanto que DIVMS, POL e lignina aumentaram. A DIVMS se mostrou negativamente correlacionada com FDN e FDN/POL, porém não houve correlação entre DIVFDN e FDN ou FDN/POL. Conclui-se que o avanço da maturidade promoveu redução na DIVFDN e aumento na DIVMS, não existindo correlação genética entre acúmulo de açúcar e digestibilidade in vitro da fibra. Os dados deste artigo indicam não ser esperado que a seleção de genótipos com maior DIVFDN do colmo altere o teor de açúcar do mesmo.

The objectives of this study were to evaluate the effect of time of harvest on chemical composition and in vitro digestibility of sugarcane genotypes, to compare chemical composition and in vitro digestibility of the stem and leaf fractions, and to determine possible correlations between chemical composition and in vitro digestibility of the whole plant in sugarcane genotypes. Nine genotypes were harvested in May and September of 2006. In May, only the whole-plant fraction was analyzed, in September the genotypes were separated in stems, leaves or whole-plant for determination of chemical composition, sucrose (POL) and in vitro digestibility. Stems had lower neutral detergent fiber (NDF) and lignin in the DM, and greater in vitro dry matter digestibility (IVDMD) than leaves. However, stems had lower in vitro NDF digestibility (IVNDFD), higher lignin in the NDF and lower crude protein (CP). The NDF and IVNDFD were reduced with advanced maturity, while IVDMD, POL and lignin were increased. IVDMD was negatively correlated with NDF and NDF/POL, however there was no correlation between IVFDND and NDF or NDF/POL. It can be concluded that with the advance in maturity the IVNDFD was reduced and IVDMD was increased, and there was no genetic correlation between accumulation of sugar and in vitro fiber digestibility. Data from this study indicate that it is not expected that selection of genotypes with greater stem IVNDFD would alter the sugar content of the plant.