Performance de híbridos simples de milho desenvolvidos de populações melhoradas por seleção recorrente recíproca modificada

Maize (Zea mays L.) elite inbred lines developed from pedigree programs tend to be genetically related. Therefore, it is necessary to incorporate unrelated inbreds to those programs to allow the continued release of outstanding single-crosses. The objectives of this research were to compare the usefulness of a modified reciprocal recurrent selection procedure (MRRS) to improve populations to be used as sources of elite inbreds and outstanding single-crosses to integrate pedigree programs, and to investigate the effects of selection on the relative contribution of general (GCA) and specific combining (SCA) abilities to the single-crosses variation. Eight and six S3 lines from populations IG-3-C1 and IG-4-C1, respectively, selected from the first cycle of the MRRS program were crossed in a partial-diallel mating design, and the 48 experimental and five commercial single-crosses were evaluated in six environments. Grain yield mean of the experimental single-crosses (9.57 t ha¹) did not differ from the commercial single-crosses (9.86 t ha¹), and ten of the 48 experimental single-crosses could be released as cultivars because they compared favorably to the currently used single-crosses. Thus, one cycle of the MRRS procedure improved efficiently the populations allowing the development of outstanding single-cross, but additional cycles of selection should be carried out since none of the experimental single-crosses outperformed the highest yielding commercial single-cross. The relative contribution of the GCA over SCA may have been affected by the MRRS, since the SCA was more important than GCA for some of the traits assessed.Linhagens elites de milho (Zea mays L.) desenvolvidas em programas genealógicos tendem a ser geneticamente relacionadas. Portanto, é necessário incorporar linhagens não relacionadas a estes programas para permitir a liberação contínua de híbridos simples superiores. Comparou-se a utilidade de um procedimento modificado de seleção recorrente recíproca (SRRM) em melhorar populações a serem utilizadas como fontes de linhagens elites e híbridos simples superiores para integrar os programas de melhoramento, e investigar os efeitos da seleção na contribuição relativa da capacidade geral (CGC) e da capacidade específica (CEC) de combinação para a variabilidade dos híbridos simples. Oito e seis linhagens S3 obtidas das populações IG-3-C1 e IG-4-C1, respectivamente, selecionadas do primeiro ciclo de SRRM, foram cruzadas no delineamento dialelo parcial e os 48 híbridos simples experimentais (HSE) e cinco híbridos simples comerciais (HSC) foram avaliados em seis ambientes. A média geral de produção de grãos dos HSE (9.57 t ha¹) não diferiu significativamente dos HSC (9.86 t ha¹), e dez dos 48 HSE poderiam ser liberados como cultivares, pois são comparáveis aos híbridos simples comerciais. Portanto, um ciclo de SRRM foi eficiente em melhorar as populações permitindo a produção de híbridos simples superiores, mas ciclos adicionais de seleção deverão ser conduzidos, pois nenhum dos HSE superou o híbrido simples comercial mais produtivo. As contribuições relativas da CGC e da CEC podem ter sido afetadas pela SRRM, uma vez que a CEC foi mais importante que a CGC para alguns caracteres avaliados

Genetic variability in popcorn synthetic population

The Brazilian popcorn has low genetic variability and the successful development of advanced lines, new popcorn cultivars with high grain yield (GY) and expansion volume (PE) is dependent on parental selection and precise determination of heterotic groups. The aim of this study was to evaluate genetic variability and identify heterotic groups in synthetic populations of popcorn, using diallel crosses. Thus, nine synthetic populations were crossed using complete diallel scheme. The GY and PE traits of 36 hybrids and reciprocals were evaluated in a randomized complete block design with 72 treatments and two replicates in two years. The effects of non-additive genes were the most important in the genetic control of these traits, indicating a favorable situation to produce hybrids. The reciprocal effect is mainly due to non-maternal effects for GY and PE. The highest GY values were obtained for the 02 x 08, 04 x 09, 05 x 09, and 01 x 09 crosses and the highest PE were obtained for the 07 x 01 and 03 x 04 crosses. The exploitation of synthetic populations from S3 lines can be an alternative to increase the genetic variability for grain yield and popping expansion in popcorn breeding programs.

Estimate of genetic parameters in Brachiaria decumbens hybrids Estimate of genetic parameters in Brachiaria decumbens hybrids ARTICLE

weight (FGW); total dry matter (TDM); speed of regrowth (SR); tiller regrowth density (TRD); regrowth ability (REG); crude protein (CP); in vitro organic matter digestibility (IVD); neutral detergent fiber (NDF) and lignin (LIG). The statistical analyses were carried out using the mixed models methods. Genetic variability for all traits assessed was detected, and estimates of individual heritability were of medium to high magnitude, indicating the possibility of gains with selection. Significant genetic correlations were observed betwee

Seed quality, chlorophyll content index and leaf nitrogen levels in maize inoculated with Azospirillum brasilense

The aim of this study was to evaluate differences between maize genotypes in relation to the germination response of the seeds and the growth of seedlings inoculated with Azospirillum brasilense, as well as the effect of inoculation on nitrogen levels and the chlorophyll content index of the leaves. The physiological seeds quality from the single-cross hybrids AG7098 and 2B707, and from the experimental synthetic varieties V2 and V4, inoculated with A. brasilense, was tested for germination, percentage and rate of emergence, and dry matter weight of the shoots and roots. Nitrogen levels and chlorophyll content index were evaluated in leaves of the same four genotypes grown in a greenhouse under different nitrogen supply systems and methods of inoculation with A. brasilense. The genotypes differ with regard to inoculation with A. brasilense. The hybrids were responsive to inoculation with A. brasilense for root dry matter weight. The V2 variety had a lower performance as regards root dry matter weight, with the opposite being seen for the dry matter weight of the shoots. V4 displayed no significant differences when inoculated. The results of the chlorophyll content index were not significant. Each genotype under evaluation displayed a different response for leaf nitrogen levels. It is possible to infer that the hybrids responded better to inoculation with the bacteria, with the greater root development leading to a better utilisation of water and nutrients.O objetivo deste estudo foi avaliar diferenças entre genótipos de milho quanto à resposta germinativa das sementes e crescimento de plântulas inoculadas com Azospirillum brasilense, assim como o efeito da inoculação no teor de nitrogênio e índice de conteúdo de clorofila foliar. A qualidade fisiológica de sementes dos híbridos simples, AG7098 e 2B707, e das variedades sintéticas experimentais, V2 e V4, inoculados com A. brasilense foi avaliada por meio de testes de germinação, porcentagem e velocidade de emergência e, massa de matéria seca de parte aérea e raiz. O teor de nitrogênio e o índice de conteúdo de clorofila foram avaliados em folhas dos mesmos quatro genótipos cultivados em casa de vegetação sob diferentes sistemas de fornecimento de nitrogênio e formas de inoculação com A. brasilense. Os genótipos diferem em relação à inoculação com A. brasilense. Os híbridos foram responsivos à inoculação com A. brasilense para massa de matéria seca de raiz. A variedade V2 apresentou comportamento inferior quanto à massa de matéria seca de raiz, mas o contrário foi observado para massa de matéria seca de parte aérea, e V4 não apresentou diferenças significativas quando inoculada. Os resultados de índice de conteúdo de clorofila não foram significativos. Para teor de nitrogênio foliar, cada genótipo avaliado respondeu de maneira particular. É possível inferir que os híbridos avaliados responderam melhor à inoculação com a bactéria, sendo que o maior desenvolvimento de raízes leva ao maior aproveitamento de água e nutrientes.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES