Genetic parameters of agronomic characters in Panicum maximum hybrids

Abstract

-This study was carried out with the objective of estimating the genetic parameters of agronomic traits in Panicum maximum hybrids. Genotypes obtained from the crosses between the sexual plants S10 and S12 and cultivars Tanzania and Mombasa were evaluated. The design was an incomplete blocks design with two replicates (clones) and 33 blocks. Each block was constituted by three lines or plots with nine plants each, which were evaluated in six harvests. All the characters presented low broad sense heritabilities for both the individual harvest and for the mean of harvests and a large difference between the heritability and the individual repeatability coefficient, which may be due to the high permanent environmental variance, mainly for forage dry matter and leaf dry matter. On the other hand, the percentage of leaves also presented low repeatability and permanent environmental variance. The genotypic coefficients of variation were high, except for leaf percentage, but they were also associated with high residual coefficients of variation. Both the broad sense heritabilities per harvest and for the mean of harvests were of moderate magnitude for the agronomic traits evaluated in hybrid individuals of P. maximum. On the other hand, there is variability for selection of important characters such as total and leaf dry matter yields and selection for leaf percentage needs a greater number of harvests to improve selection efficiency. The genotypes presented great variability for Bipolaris maydis leaf spot incidence and this character can be included in the P. maximum breeding program.

Estimate of genetic parameters in Brachiaria decumbens hybrids

“…Gains with selection should be high for productivity during the dry season in this population, since FGW and TDM showed high magnitudes of heritability estimates, 0.74 and 0.65, respectively. These estimates were of greater magnitude than those observed for B. humidicola and Panicum maximum (Figueiredo et al 2012, Braz et al 2013, also evaluated for TDM in the dry season.…”

“…The opposite happened for REG with estimates of 0.37 for the dry and 0.42 for the rainy season (Table 1). Estimates of low magnitude of r i for REG were also observed for Panicum maximum in a joint analysis considering seven clippings (Braz et al 2013). …”

“…Several papers in the literature have already described the positive correlation among agronomic traits, such as FGW and TDM, among nutritive value traits, such as NDF and LIG, the positive correlation between CP and IVD, and the negative correlation between NDF and LIG (Figueiredo et al 2012, Braz et al 2013. This happens because these nutritional components are directly related to the morphological structure of the plant.…”

Genotypic value in hybrid progenies of Panicum maximum Jacq.

“…Also, according to these authors, the hybrids with worst performance were those from the S12 × T110 cross. Trend of progenies originating from the most productive parents obtaining greater TDM and LDM in the P. maximum species is related to the considerable level of heritability reported for these parameters (RESENDE et al, 2004;BRAZ et al, 2013).…”

Sanitary analysis, transmission and pathogenicity of fungi associated with forage plant seeds in tropical regions of Brazil

“…The leaf spots presented characteristics of damages caused by Bipolaris sp. In general, other studies report the susceptibility of these grasses to attacks of fungi from genre Bipolaris, Exserohilum and Curvularia, which cause spots in leaves and stalks, besides drying the leaves and killing the seedlings (Macedo and Barreto, 2007;Martinez et al, 2010;Kleczewski et al, 2012;Braz et al, 2013;Kumar et al, 2013), however, some authors realized that this result may vary in accordance with the genotype used (Braz et al, 2013). Yago et al (2011) observed that there was an increase in the seedling death percentage for sorghum and foxtail millet seeds inoculated with Curvularia lunata and increase in the severity index for infected seedlings 10 days after the inoculation.…”