Abstract The selection of sexual genitors in Urochloa decumbens breeding is dependent upon the performance of their progeny simultaneously for several traits. Thus, our objectives were to (i) compare the efficiency of indices to select genitors of U. decumbens, (ii) evaluate the genetic gains obtained through selection intensities, and (iii) evaluate the multivariate pattern of progenies through principal components analysis (PCA). For this purpose, 1415 hybrids from 75 progenies of full siblings were evaluated at Embrapa Beef Cattle (Brazil) using seven cuts for dry matter production, regrowth, protein, fiber, lignin, and percentage digestibility. Statistical analyses were performed using mixed models and PCA. The direct selection for dry matter production provided a 37.51% genetic gain. Agronomic traits using indices provided greater gains. Genitors selected using PCA Biplot were similar to selections using indices. Indices and PCA were proven to be an excellent tool to select multi-traits in U. decumbens.

ABSTRACT. 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.

Abstract Breeding new maize varieties that take up more N from the soil and increase N fixation is a crucial source of combined nitrogen in agricultural systems. Thus, this study aimed to select superior maize parental lines efficient in the use of nitrogen and Azospirillum brasilense. Three experiments were conducted in two agricultural seasons aiming to allocate all diallel hybrids in three different nitrogen conditions. The experiments were performed in a RCB design with two replications, and the diallel was analyzed using the mixed model approach. The general combining ability and Azospirillum use efficiency were applied to select the best parental line. The most promising hybrid combinations were “I-08 x II-06”, “I-02 x II-04”, and “I-01 x II-02”. Parents involved were selected for the development of hybrids. Parents I-01, I-02, I-08, II-01, II-02, II-04, II-05, and II-06 were selected to explore the basic population in the A. brasilense-use efficiency breeding program.

RESUMO A eficiência de seleção pode ser ampliada para determinado caráter utilizando-se estimativas de parâmetros genéticos, as quais são fundamentais no melhoramento de plantas, uma vez que permitem identificar a natureza da ação dos genes envolvidos no controle de caracteres quantitativos e avaliar a eficiência de diferentes estratégias de melhoramento para a obtenção de ganhos genéticos. Assim, objetivou-se verificar a existência de variabilidade e correlação entre caracteres agronômicos e morfológicos em populações sintéticas de milho, visando seleção indireta. Foram utilizadas 13 populações, avaliadas em experimentos de campo em Jaboticabal-SP e Campo Alegre de Goiás-GO, utilizando-se o delineamento em blocos casualizados, para acamamento (AC), quebramento de colmos (QUE), altura de plantas (AP), altura de espiga (AE), e produção de grãos (PG). As 13 populações também foram semeadas em sacos plásticos de 1 kg sob sombrite, utilizando-se delineamento em blocos casualizados com nove repetições, para avaliação das seguintes características morfológicas: comprimento da raiz principal (CR), matéria fresca de raiz (MFR), matéria seca de raiz (MSR), diâmetro médio de raiz (DMR), área de superfície da raiz (ASR), densidade de tecido radicular (DTR) e matéria seca da parte aérea (MSPA). O caráter PG apresentou grande variabilidade genética, indicando ser eficiente se utilizado para seleção. A seleção sobre os caracteres morfológicos é mais indicada sobre MSR, devido à facilidade e precisão na obtenção dos dados, alta correlação com todos os outros caracteres morfológicos e sua associação com PG. A seleção simultânea com base em MFR e MSR, para ganhos na PG, pode ser realizada. Os caracteres AC e QUE são os que apresentam maior efeito direto sobre a PG, sendo indicados para seleção indireta.

ABSTRACT The efficiency of selection can be broadened for certain traits using estimative of genetic parameters, which are fundamental for plant breeding. The estimative of genetic parameters allows identifying the nature of the action of genes involved in the control of quantitative traits and evaluates the efficiency of different breeding strategies to obtain genetic gains. Therefore, this study aimed to verify the variability and correlation between morphological and agronomic traits in synthetic maize populations, in order to practice indirect selection. Thirteen populations were evaluated in field experiments at Jaboticabal- SP and Campo Alegre de Goiás-GO, using randomized block design, for lodging (LOD), culm breakage (CB), plant height (PH), ear height (EH) and grain yield (GY). The 13 populations were also sown in 1 kg-plastic bags under black shade cloth, using a randomized complete block design with nine replications, for evaluation of the morphological traits: main root length (MRL), root fresh matter (RFM), root dry matter (RDM), average root diameter (ARD), root surface area (RSA), root tissue density (RTD) and shoots dry matter (SDM). The trait GY exhibited genetic variability enough to be effective if used for selection. The selection on the morphological traits is indicated on RDM, due to the ease in obtaining data and its accuracy, high correlation with all morphological traits and association with GY. The simultaneous selection based on RFM and RDM, for gains in GY, can be performed. The highest direct effect on GY was identified in LOD and CB, being indicated for indirect selection.

Abstract The objective of this study was to estimate genetic parameters for agronomic traits and nutritional value in intraspecific hybrids of B. decumbens. For this, a population of 1,415 hybrids was evaluated in field plots at Embrapa Beef Cattle in Campo Grande/MS/Brazil, with seven clippings in order to estimate field green 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 between FGW and TDM (0.99), TDM and SR (0.81), TDM and IVD (-0.71), TDM and LIG (0.71), and CP and IVD (0.70).

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.

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.

O objetivo deste trabalho foi estudar a herança da senescência retardada em milho. Foram realizados cruzamentos dialélicos parciais entre 50 linhagens e cinco testadores. Os 250 cruzamentos resultantes, além de seis híbridos comerciais utilizados como testemunhas, foram avaliados em oito ambientes, no delineamento látice simples 16x16, com duas repetições por ambiente. Os cruzamentos dialélicos foram analisados utilizando o método 4 do modelo 1 de Griffing, adaptado para múltiplos ambientes. A contribuição da capacidade geral de combinação (CGC) para a expressão do caráter "stay-green" (69,06%) foi maior que a da capacidade específica de combinação (CEC) (30,94%), evidenciando que os efeitos aditivos são mais importantes que os efeitos não aditivos na expressão deste caráter. Tanto a CGC como a CEC interagiram significativamente com o ambiente, indicando que a seleção para este caráter deve ser realizada com base nas médias de experimentos em diversos ambientes.

The objective of this research was to study the inheritance of delayed senescence in maize. Partial diallel crosses among 50 inbred lines and five testers were made. The 250 crosses, along with six commercial hybrids used as checks, were evaluated at eight environments in lattices 16x16 with two replications per environment. The diallel crosses were analyzed following the method 4 model 1 of Griffing, extended to multiple environments. The contribution of the general combining ability (CGA) for the expression of the stay-green trait (69.06%) was greater than the specific combining ability (SCA) (30.94%), showing that additive effects are more important than non-additive effects for the expression of this trait. Both GCA and SCA interacted significantly with the environments, indicating that the selection for this trait should be based on the means across environments.

This paper reports the effects of three cycles of reciprocal recurrent selection (RRS) on the means, genetic variances, and on the genetic correlations for several traits in the IG-1 and IG-2 maize (Zea mays L.) populations. Interpopulation full-sib progenies from cycle zero (C0) and from cycle 3 (C3) of RRS were evaluated in two locations. RRS was highly effective to improve the traits according the objectives of the program: grain yield and prolificacy increased significantly, while plant height, ear height, and ear placement decreased significantly. Genetic variances for all traits decreased significantly from C0 to C3, but the genetic correlations did not change consistently across the cycles of selection. The expected responses to the fourth cycle of RRS and the probability of selecting double-crosses from C3 that outperform those from C0 showed that the decreases in the genetic variances were not great enough to limit the continued improvement of the populations as well as the use of the improved populations as sources of inbred lines to develop commercial hybrids. However, if the magnitudes of the genetic variances continue to decrease, new sources of improved germplasm should be incorporated into both populations to allow the continued improvement of the interpopulation by RRS.