Parâmetros genéticos, repetibilidade e diversidade genética em híbridos de Panicum maximum

• Ano de defesa: 2012
• Autor(a) principal: Braz, Thiago Gomes dos Santos
• Orientador(a): Fonseca, Dilermando Miranda da
• Banca de defesa: Martuscello, Janaina Azevedo , Queiroz, Domingos Sávio
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Zootecnia
• Departamento: Genética e Melhoramento de Animais Domésticos; Nutrição e Alimentação Animal; Pastagens e Forragicul
• País: BR
• Palavras-chave em Português: Melhoramento; Gramínea; Família de irmãos completos; Produção de forragem; Repetibilidade
• Palavras-chave em Inglês: Improvement; Grassy; Full-sib family; Forage production; Repeatability
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::PASTAGEM E FORRAGICULTURA
• Link de acesso: http://locus.ufv.br/handle/123456789/1798

This study was carried out with the aim to evaluate the repeatability, genetic parameters and genetic diversity of Panicum maximum hybrids. The experiment was conducted in the experimental area of Embrapa Gado de Corte during the period from December, 2009 to February, 2011. Were evaluated hybrids form three complete sib progenies resulted of the crosses among the genitors S10 and guinea grass cv. Tanzania, S10 and guinea grass cv. Mombaça and S12 with guinea grass cv. Tanzania. After the establishment of the hybrids in the field were obtained the final number of 108 hybrids to progeny 1, 167 hybrids to progeny 2 and 45 hybrids to progeny 3, totaling 320 genotypes, which were cloned and evaluated in an clonally test with two replicates. The blocks were constituted for three linear plots with nine plants (bunches). In the borderline were used guinea grass cv. Mombaça plants. The spacing between plants into the lines and among lines was of 1 m. The hybrids were cut at 25 cm from the soil level in the months January, March, June, October, November, December, 2010 and in February 2011. The harvest made in June was not evaluated. In the repeatability study were evaluated the characters: dry matter yield (DMY), leaf yield (LY), stems + sheath yield (SY) and percentage of leaves (%L).Were evaluated the characters plant height (PH), regrowth (REG) and Bipolars maydis incidence (BMI). The repeatability coefficient were estimated by the methods of: variance analysis (ANOVA), principal components based on variance and covariance matrix (PCCOV), principal components analisys based on correlation matrix (PCCOR) and structural analysis based on the correlation matrix (SACOR). The LY had the highest repeatability followed by DMY and PH. In the morphoagronomic characters it was observed the highest repeatability for PH. The progenies were different in repeatability of REG and BMI. Six harvests were sufficient to provide reliability in the selection of P. maximum hybrids for DMY, LY and BMI. The repeatability of harvestes of %L is low. The evaluation of plots provides results slightly higher than the evaluation of individual plants for all characters, in exception to regrowth. The increasing in selection efficiency resulted in considerable increase in the number of measurements, especially for characters with low repeatability. In the genotypic stabilization analysis were used the characters DMY, LY, SY and %L in both sites of evaluation, plants and plots. Generaly, the higest repeatabilities were observed for DMY and LY, mainly when the harvests 4, 5 and 6 were considered. The LY had the highest reapeatability and determination coefficients. The repeatability of SY and %L were considered low magnitude, mainly with the inclusion of the harvest realized during the dry season. The harvests realized during the rainy season resulted in higher repeatability and determination coefficient for the genotypic selection and the inclusion of dry season harvest was detrimental for the selection of low repeatability characters like %L. Evaluations of genotypic stabilization in plots result in higher repeatability than the plant evaluation during the rainy season. The genetic parameters were estimated for the agronomic characters: DMY, LY and SY and for the morphoagronomical characters: %L, PH, REB and BMI. The components of genetypic variance, among plots variance and permanent environment variance were statistically significant for all characters evaluated (P<0.05), in exception to %L where the permanent environment variance was not statistically significant (P>0.05). All characters had moderate heritability of harvests and heritability of médium and a high difference between the heritability and individual repeatability. It could be explained by the occurrence of permanent environment variance, particularly for DMY and LY. In the other hand, %L showed low individual repeatability and permanent environment variance. The genotypic coefficient of variation was high in all characters in exception to %L, but all of them were associated to high residual coefficient of variation. Both the heritability of harvests and the heritability of medium of the agronomic characters were considered of low to moderate magnitude in the P. maximum hybrids. On the other hand, we could conclude there is genetic variability for the selection of important breeding characters like LY and the selection of %L demand more harvests for improve eficiency. The hybrid genetypes showed high variability for B. maydis incidence. The genetic diversity study was realized in different progenies using different group of characters (morphologic, agronomic and nutritive value). With these results, we could conclude that the morphologic characters plant height, haid density in the sheath, length of hair in the leaf, purple color of the sheath, glaoucousness and kind of leaf; the agronomic characters LY, %L and BMY; and the nutritive value characters: cellulose, silica and lignin in potassium permanganate are usefull descriptors for the study of genetic diversity in P. maximum hybrids. With the principal component analisys it was possible to observe that there is more variability among the individuals within the progenies than among the progenies. In the cluster analisys it was observed more groups when agronomic traits were used. It was possible to identify with the dissimilarity matrix, divergente individuals for more than group of variables and with good performance for the recombination in the P. maximum breeding program.