Capacidade combinatária de linhagens e seleção de híbridos eficiente no uso de Azospirillum brasilense e nitrogênio em milho
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2017-11-10
Autores
Buzinaro, Rodolfo [UNESP]
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Universidade Estadual Paulista (Unesp)
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O nitrogênio é um dos elementos mais exigidos pela cultura do milho, pois está diretamente ligado à capacidade de produção agrícola desta espécie. Grande parte dos solos brasileiros agricultáveis possuem deficiência de nitrogênio ou este nutriente não está disponível em quantidades suficientes para suprir a necessidade da cultura, sendo necessário realizar aplicações suplementares de nitrogênio para se alcançar elevadas produtividades. As cultivares atuais de milho são altamente dependentes de adubação nitrogenada, pois foram desenvolvidas para ambientes otimizados, não sendo adaptadas para as condições de cultivo sob baixo nitrogênio. O uso de bactérias diazotróficas, as quais possuem a capacidade de fixar nitrogênio e disponibilizá-lo para as plantas, bem como a associação das plantas com essas bactérias, pode se tornar uma alternativa sustentável e economicamente viável para a produção de milho em sistemas agrícolas sob baixa utilização de nitrogênio. Com base no exposto, os objetivos deste trabalho foram identificar e caracterizar genótipos de milho eficientes no uso do nitrogênio e Azospirillum brasilense em ambientes contrastantes quanto a disponibilidade de nitrogênio no solo e selecionar parentais superiores de milho para eficiência no uso de Azospirillum brasilense. Foram utilizados como material genético 48 genótipos de milho obtidos em esquema de dialelo parcial, utilizando-se oito linhagens parentais pertencentes ao grupo heterótico I, e seis linhagens parentais pertencentes ao grupo heterótico II, todas provenientes do Departamento de Genética da ESALQ/USP. Os experimentos foram conduzidos em três safras (primeira safra 2013/2014 e 2014/2015 e segunda safra 2014) no delineamento de blocos casualizados com duas repetições e três testemunhas. Em cada safra foram realizados três experimentos, os quais eram diferenciados pela aplicação com A. brasilense, aplicação de nitrogênio em cobertura e sem nenhuma aplicação, respectivamente. Os caracteres avaliados foram altura de planta, altura de espiga, florescimentos masculino e feminino, tombamento, produtividade de grãos, peso médio de grãos, número de grãos por fileira, número de fileiras de grãos e, diâmetro e comprimento de espiga. Os índices de eficiência no uso de A. brasilense foram obtidos utilizando os dados referentes aos experimentos com A. brasilense e sem aplicação, para todos os caracteres avaliados. Pela análise dialélica os efeitos aditivos foram mais importantes do que os efeitos não-aditivos para a eficiência no uso de A. brasilense para a maioria dos caracteres, com exceção do peso médio de grãos sob inoculação. Os genótipos do grupo heterótico II apresentaram maior concentração e acúmulo de genes favoráveis para a EUAz eficiência. Os genitores 6 e 8 do grupo heterótico I e os genitores 2’ e 5’ do grupo heterótico II, são os que apresentaram melhores estimativas de capacidade geral de combinação, enquanto o cruzamento 8x6’ apresenta maior estabilidade e complementariedade gênica para eficiência no uso de A. brasilense para a produtividade de grãos. A partir das análises dialélicas por modelos mistos para a produtividade de grãos, as combinações 8 x 6’, 2 x 4’ e 1 x 2’ e os parentais envolvidos nesses cruzamentos foram selecionados para desenvolvimento de híbridos. Os genitores 1, 2, 8 do grupo heterótico I e 1’, 2’, 4’, 5’ e 6’ do grupo heterótico II foram selecionados para formar população base para o programa de melhoramento genético para eficiência no uso de Azospirillum brasilense. Pela análise GGE biplot, para a característica produtividade de grãos, constatou-se que os genótipos 11, 5, 12 e 19 são os mais promissores para a eficiência no uso de A. brasilense. O genótipo dialélico 11 é o mais próximo do “genótipo ideal” dentre o conjunto dos genótipos avaliados. Os ambientes sob aplicação de A. brasilense possuem maior capacidade de discriminar os genótipos.
The nitrogen is one of the elements most required by maize crop because it is directly related to the agricultural production capacity of this species. Most brazilian soils have nitrogen deficiency or it is not available in sufficient quantities to meet the need of the crop, and it is necessary to make supplemental nitrogen applications to reach high yields. The current maize cultivars are highly dependent on nitrogen fertilization since they were developed for optimized environments and were not adapted to the conditions under low nitrogen cultivation. The use of diazotrophic bacteria, which have the ability to fix nitrogen and make it available to plants, as well as the association of plants with these bacteria, can become an ecologically sustainable and economically viable alternative for the production of corn in agricultural systems under low or non-use of nitrogen. Thus, the objectives of this study were to identify and characterize efficient maize genotypes in the use of nitrogen and Azospirillum brasilense in contrasting environments regarding nitrogen availability in the soil and to select higher parental maize for efficiency in the use of Azospirillum brasilense. Were used as genetic material 48 diallelic genotypes were obtained in a partial diallel scheme, using eight lines belonging to the heterotic group I, and six lines belonging to the heterotic group II, all from the Department of Genetics of ESALQ / USP. The experiments were conducted in three crops in a randomized block design with two replicates and three controls. In each season, three experiments were carried out, in which they were differentiated by the application of A. brasilense, application of nitrogen in coverage and without any application, respectively. The evaluated traits were plant height, ear height, male and female blossoms, tipping, grain yield, mean grain weight, number of grains per row, number of rows of grain and diameter and length of the spike. The indices of efficiency in the use of A. brasilense were obtained using the data referring to the experiments with A. brasilense and without application, for all evaluated characters. By conventional diallel analysis the additive effects were more important than the non-additive effects for the efficiency in the use of A. brasilense for most of the characters, except for the average grain weight. The genotypes of the heterotic group II present greater concentration and consistency of genes favorable for this efficiency. The heterotic group I and the heterotic group I and the heterotic group I and the heterotic group II, are the ones that present the best estimates of overall combining ability, while the 8x6 'crossroads present greater stability and gene complementarity for efficiency in the use of A. brasilense. From diallel analyzes by mixed models the combination 8 x 6’, 2 x 4’, 1 x 2’ and parents involved in these crosses were selected for development of hybrids. The genitors 1, 2, 8 from the heterotic group I and 1’, 2’, 4’, 5’ and 6’ from the heterotic groups II were selected to explore basic population in A. brasilense-use efficiency breeding program. From the GGE biplot analysis, for the characteristic grain yield, it was contacted that the diallel genotypes 11, 5, 12 and 19 are the most promising for the efficiency in the use of A. brasilense. The diallelic genotype 11 is the closest to the "ideal genotype" among the set of diallel genotypes evaluated. The environments under application of A. brasilense have a greater ability to discriminate the genotypes.
The nitrogen is one of the elements most required by maize crop because it is directly related to the agricultural production capacity of this species. Most brazilian soils have nitrogen deficiency or it is not available in sufficient quantities to meet the need of the crop, and it is necessary to make supplemental nitrogen applications to reach high yields. The current maize cultivars are highly dependent on nitrogen fertilization since they were developed for optimized environments and were not adapted to the conditions under low nitrogen cultivation. The use of diazotrophic bacteria, which have the ability to fix nitrogen and make it available to plants, as well as the association of plants with these bacteria, can become an ecologically sustainable and economically viable alternative for the production of corn in agricultural systems under low or non-use of nitrogen. Thus, the objectives of this study were to identify and characterize efficient maize genotypes in the use of nitrogen and Azospirillum brasilense in contrasting environments regarding nitrogen availability in the soil and to select higher parental maize for efficiency in the use of Azospirillum brasilense. Were used as genetic material 48 diallelic genotypes were obtained in a partial diallel scheme, using eight lines belonging to the heterotic group I, and six lines belonging to the heterotic group II, all from the Department of Genetics of ESALQ / USP. The experiments were conducted in three crops in a randomized block design with two replicates and three controls. In each season, three experiments were carried out, in which they were differentiated by the application of A. brasilense, application of nitrogen in coverage and without any application, respectively. The evaluated traits were plant height, ear height, male and female blossoms, tipping, grain yield, mean grain weight, number of grains per row, number of rows of grain and diameter and length of the spike. The indices of efficiency in the use of A. brasilense were obtained using the data referring to the experiments with A. brasilense and without application, for all evaluated characters. By conventional diallel analysis the additive effects were more important than the non-additive effects for the efficiency in the use of A. brasilense for most of the characters, except for the average grain weight. The genotypes of the heterotic group II present greater concentration and consistency of genes favorable for this efficiency. The heterotic group I and the heterotic group I and the heterotic group I and the heterotic group II, are the ones that present the best estimates of overall combining ability, while the 8x6 'crossroads present greater stability and gene complementarity for efficiency in the use of A. brasilense. From diallel analyzes by mixed models the combination 8 x 6’, 2 x 4’, 1 x 2’ and parents involved in these crosses were selected for development of hybrids. The genitors 1, 2, 8 from the heterotic group I and 1’, 2’, 4’, 5’ and 6’ from the heterotic groups II were selected to explore basic population in A. brasilense-use efficiency breeding program. From the GGE biplot analysis, for the characteristic grain yield, it was contacted that the diallel genotypes 11, 5, 12 and 19 are the most promising for the efficiency in the use of A. brasilense. The diallelic genotype 11 is the closest to the "ideal genotype" among the set of diallel genotypes evaluated. The environments under application of A. brasilense have a greater ability to discriminate the genotypes.
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Palavras-chave
Zea mays, bactéria diazotrófica, análise dialélica, REML/BLUP, GGE biplot, interação GxA, diazotrophic bacteria, diallel analysis, interaction GxE