Contribuições genéticas e ambientais para aumento do rendimento do trigo em Minas Gerais, Brasil

Producers need wheat cultivars adapted to the predominant climate conditions of the end of the rainy period. Having this in mind, EPAMIG (Agriculture and Livestock Research Institute of Minas Gerais) has been developing a wheat genetic improvement program since 1976, and the estimates of the genetic improvement established by the breeding programs could be useful to quantify their efficiency. This study focused on the quantification of the genetic progress achieved by these improvement programs of dryland wheat in the Brazilian-savanna between 1976 and 2005. The efficiency of these programs was evaluated based on grain yield data of VCU (Value for Cultivation and Use) trials conducted at ten locations in the Minas Gerais State, Brazil. The mean estimated genetic progress for mean grain yield between 1976 and 2005 was 37 kg ha-1 year-1. The genetic yield gain in the study period indicates that the improvement programs of dryland wheat in the Brazilian-savanna are effective. Besides the marked contribution of genetic gain, the environmental and technological improvements were also relevant for the yield, accounting for 47.4% of the total progress in the period. The improvement programs of dryland wheat resulted in a genotype renovation rate of 35% over the years.Devido à necessidade dos produtores por cultivares de trigo adaptados às condições climáticas do final da época das chuvas, desde 1976 a EPAMIG (Empresa de Pesquisa Agropecuária de Minas Gerais) vem desenvolvendo um programa de melhoramento genético. As estimativas dos progressos genéticos alcançados pelos programas de melhoramento são instrumentos hábeis para se quantificar a eficiência dos trabalhos executados. Quantificou-se o progresso genético obtido pelos programas de melhoramento do trigo de sequeiro no cerrado brasileiro no período de 1976 a 2005 utilizando-se resultados de produtividade de grãos obtidos nos ensaios de valor de cultivo e uso. O progresso genético médio anual estimado no período de 1976 a 2005 foi de 37 kg ha-1 ano-1 na produtividade média de grãos. O ganho genético, em produtividade, obtido no período estudado, indica que os programas de melhoramento de trigo de sequeiro no cerrado brasileiro são eficientes. Apesar de o ganho genético ter contribuído expressivamente, as melhorias ambientais e tecnológicas foram importantes para o acréscimo na produtividade, representando 47,4% do progresso total obtido. Os programas de melhoramento de trigo de sequeiro promovem 35% de renovação de genótipos ao longo dos anos

Genetic control and tolerance to the heat stress in wheat hybrid population and cultivars

O objetivo deste trabalho foi obter informações sobre o controle genético da produtividade de grãos de trigo sob condições de estresse de calor, o grau de tolerância ao estresse de calor de algumas cultivares e linhagens e a identificação de populações segregantes promissoras para a obtenção de linhagens adaptadas às condições da região central do Brasil. Foram avaliados 13 parentais e 40 populações provenientes de um dialelo parcial, nas gerações F1 e F2 em condições de campo, em Lavras e Patos de Minas, MG, com as semeaduras feitas no verão (fevereiro) e no inverno (maio). Houve diferença de tolerância ao calor entre os parentais e entre as populações híbridas quanto ao caráter produção de grãos, e ambos os efeitos aditivos e não-aditivos foram importantes no controle genético deste caráter na presença ou ausência de calor. Apesar da ocorrência de interações popu-lações x épocas de semeadura, a alta repetibilidade dos efeitos da capacidade geral de combinação permite inferir a possibilidade de acelerar os programas de melhoramento na região, efetuando-se a seleção tanto na época de verão quanto no inverno.The objective of this work was to get information about the genetic control of the grain yield under heat stress conditions, the tolerance of cultivar and the identification of promising segregation populations for selections of lines adapted to the conditions of the central region of Brazil. Thirteen parents and 40 populations in F1 and F2 generations derived by partial diallel crosses were evaluated. The experiments were conducted under field conditions in Lavras and Patos de Minas, MG, Brazil, sowing the seeds in the summertime (February) and in the winter (May). There was difference of heat tolerance among parents and hybrid populations for grain yield character, and both additive and non-additive effects were important in the genetic control of grain yield character in the presence or absence of heat. In spite of the occurrence of populations x sowing time interactions, the high repeatability of the effects of the general combining ability suggests the possibility of the selection in the summertime and winter facilitating to advance the breeding programs in the region

Genotypes and environments interaction and its implication in gain with wheat selection

O objetivo deste trabalho foi quantificar o componente da interação genótipos x ambientes e avaliar seus reflexos no progresso genético com diferentes critérios de seleção de linhagens de trigo adaptadas às condições do Brasil Central. Foram avaliadas 240 famílias F2:4 oriundas de oito populações segregantes de trigo. Os experimentos foram conduzidos em campo, com semeaduras realizadas no verão e no inverno, em 2004. Foi utilizado o delineamento em látice com duas repetições. Avaliaram-se os caracteres espigamento, altura de planta, massa do grão e produtividade de grãos. Realizou-se a decomposição da interação genótipos x ambientes e foram estimados os ganhos com a seleção nos dois ambientes. O grau de tolerância ao calor foi determinado com base em dois índices. A porcentagem da interação de natureza complexa foi maior do que a simples, e ganhos com seleção indireta, em um ambiente, não foram eficientes, principalmente quanto à produtividade de grãos. Apesar da interação genótipos x ambientes, o uso do índice de tolerância ao calor com base na regressão permite detectar genótipos produtivos sob condição de estresse de calor, pela melhoria da adaptabilidade dos genótipos a esse ambiente, sem alterar o comportamento desses genótipos em condições favoráveis.The objective of this work was to quantify the component of the genotypes x environments interaction, as well as to evaluate its reflexes on the genetic progress with different selection criteria for those wheat lines adapted to the Brazilian midland conditions. Two hundred and forty F2:4 families descending from eight segregant populations of wheat were evaluated. Experiments were conducted under field conditions, and sowings were accomplished in the summer and winter, 2004. The lattice design was used with two replicates. The following characters were evaluated: earing, plant height, grain weight, and grain yield. Decomposition of the genotypes x environments interaction was performed, and the gains with selection in both environments were estimated. The determination of the tolerance level to the heat was based on two indexes. The percentage of the complex-nature interaction was higher than the simple one, whereas the gains with indirect selection in an environment were not efficient, mainly for grain yield. Although the genotypes x environments interaction, use of the tolerance index to the heat based on regression allows detecting the productive genotypes under heat stress by the improvement of the genotype adaptability to this environment, without changing these genotypes' behavior under favorable conditions

Methods of adaptability and stability analysis in irrigated rice genotypes in Minas Gerais, Brazil

The objective of this study was to compare different estimation methods of adaptability and stability in ninegenotypes of irrigated rice. The experiment was conducted at three sites in the state of Minas Gerais in the growing seasonsfrom 2000/2001 to 2005/2006, totaling 11 environments. The adaptability and stability were analyzed by the methods proposedby Eberhart and Russel (1966), Cruz et al. (1989), Carneiro (1998) and Annicchiarico (1992). The methods proposed byCarneiro (1998) and by Annicchiarico (1992) were more satisfactory due to the measure of behavioral adaptability andstability, which combined adaptation, adaptability and stability concepts in just one parameter. General adaptability wasobserved in the lines CNAi 8872 and CNAi 8874 and specific adaptability to favorable conditions in cultivar Rio Grande

Recurrent selection as breeding strategy for heat tolerance in wheat

The development of heat-tolerant varieties is an important goal of wheat breeding programs, requiringefficient selection methods. In the present study the use of recurrent selection was evaluated as a strategy to improve heatstress tolerance in wheat. Two cycles of recurrent selection were performed in experiments conducted in research areas of theUniversidade Federal de Viçosa, located in Coimbra-MG and Viçosa-MG, in 2004 and 2007, in two growing seasons (summerand winter). The genetic gain and the existence of variability show the possibility of successful recurrent selection for heattolerancein wheat

POTENTIAL OF F3:4 SEGREGATING WHEAT POPULATIONS FOR TOLERANCE TO HEAT STRESS

Heat is one of the major abiotic stresses that affect wheat yield and quality in many parts of the world. To overcome this problem, the development of heat tolerant cultivars has been shown to be one of the main targets of breeding programs, especially for the conditions of Central Brazil. The present study was developed with objective of identifying promising populations for tolerance to heat stress, in order to obtain lines adapted to the conditions of Central Brazil. The experiment was carried out in the summer of 2011 in Coimbra/MG where 36 segregating populations with different numbers of families per population were evaluated in an augmented block design, determining the cycle, plant height and grain yield. Genetic variability for heat tolerance was observed among the wheat populations. The vegetative development stage of wheat was more sensitive to the effect of heat stress. The most promising segregating populations were IAC364/BRS207, IAC24/Aliança IAC24/Pioneiro that associated high yield with a large number of families selected among the most productive, demonstrating the possibility of selecting heat stress-tolerant lines

Tolerance to thermic stress in wheat genotypes

O objetivo deste trabalho foi verificar o efeito do estresse térmico sobre a cultura do trigo e avaliar o grau de tolerância de genitores e populações segregantes a esse estresse, de modo a identificar populações promissoras para obtenção de linhagens adaptadas às condições de Brasil Central. Foi utilizado o sistema de dialelo circulante, com oito genitores das cultivares Aliança, Anahuac, BH 1146, BR 24, BRS 207 e Pioneiro e as linhagens CPAC 9662 e EP 93541. Foram avaliadas 30 famílias F2:4, oriundas de cada uma das oito populações segregantes, e os oito genitores. Os experimentos foram conduzidos em campo, em 2004, com semeadura no verão (condição de estresse térmico) e no inverno (condição favorável). Foi utilizado o delineamento em látice com duas repetições. Avaliaram-se os caracteres ciclo até o espigamento, altura de planta, peso médio do grão e produção de grãos. A alta temperatura causou redução em todos os caracteres avaliados e os efeitos do estresse térmico, ocorridos no verão, foram obtidos pela porcentagem dessa redução em comparação ao cultivo de inverno. Houve diferenças entre genótipos nas duas épocas de semeadura. Os materiais mais tolerantes ao calor foram os genitores Anahuac, BH 1146, BR 24 e EP 93541, e as populações segregantes Aliança/EP 93541, EP 93541/CPAC 9662 e BH 1146/BR 24.The objective of this work was to verify the effect of thermic stress conditions on the wheat culture, to evaluate the tolerance level of parents and segregant populations to these conditions, as well as to identify promising populations in order to obtain lines adapted to the Brazilian Central region. A circulant dialel was used among eight parents, comprising the cultivars Aliança, Anahuac, BH 1146, BR 24, BRS 207 and Pioneiro; and the lines CPAC 9662 and EP 93541. Thirty F2:4 families descending from the eight segregant populations and the eight genitors were evaluated. Experiments were carried out in the field and the sowings were performed in the summer (heat stress condition) and winter (favorable condition) of 2004. The lattice design with two replicates was used. Days to heading, plant height, average grain weight, and grain yield were evaluated. In the summer, high temperature reduced all characters evaluated, and thermic stress effects were determined by that reduction percent in comparison to winter cropping values. Differences among genotypes in both sowing dates were also observed. The most heat-tolerant materials were the parents Anahuac, BH 1146, BR 24 and EP 93541, and the segregant populations Aliança/EP 93541, EP 93541/CPAC 9662, and BH 1146/BR 24

Selection of okra parents based on performance and genetic divergence

A total of 200 okra accessions with wide variability and a potential for genetic improvement were stored in the Vegetables Germplasm Bank of the Federal University of Viçosa (UFV-BGH) in Viçosa, Minas Gerais State, Brazil. The objective of this work was to select parents by genetic divergence and behavior per se in 70 okra accessions from the BGH-UFV by quantitative and qualitative descriptors of economic interest. Analysis of individual and combined variance, by clustering of means by Scott-Knott test, of the accessions by Tocher’s method and selection based on qualitative descriptors and behavior per se using the methodology of sum of inverted positions was made. The variability of the characteristics of the accessions as verified by the Scott-Knott test formed different groups and subgroups by Tocher’s method. Fifteen accessions were selected with the qualitative descriptors, and based on the sum of inverted positions for quantitative descriptors the BGH-132, BGH-547, BGH-693, BGH-740, BGH-961, BGH-7863, BGH- 7865, BGH-3196 and BGH-4890 okra accessions were selected as potential parents.Key words: Abelmoschus esculentus (L.) Moench, germplasm bank, genetic resource, genetic improvement

Genetic progress obtained by upland rice breeding in twenty one years of research in the State of Minas Gerais, Brazil

Este trabalho objetivou estimar o ganho genético obtido pelo programa de melhoramento de arroz de sequeiro (Oryza sativa L.) desenvolvido em Minas Gerais cooperativamente pela Epamig/Embrapa-Centro Nacional de Pesquisa de Arroz e Feijão (CNPAF)/UFLA/UFV, no período de 1974/75 a 1994/95. Para tanto, utilizaram-se os dados dos ensaios comparativos avançados de cultivares e linhagens de arroz de sequeiro conduzidos no referido período. Em virtude da distribuição irregular de chuvas e da resposta diferenciada dos materiais de ciclos diferentes às condições climáticas, optou-se por dividi-los em dois grupos; um contendo os genótipos precoces e o outro os de ciclo médio. Os resultados alcançados mostraram que ocorreu um ganho genético médio anual de 1,26% e de 3,37% em relação ao grupo precoce e ao de ciclo médio, respectivamente. O grupo precoce superou estatisticamente (P£0,01) em produtividade de grãos o grupo de ciclo médio, indicando que em Minas Gerais deve-se dar preferência ao plantio de cultivares de ciclo curto.This work aimed to estimate the genetic gain obtained by the upland rice (Oryza sativa L.) breeding program developed in Minas Gerais State, Brazil, in cooperation with Empresa de Pesquisa Agropecuária de Minas Gerais (Epamig), Embrapa-Centro Nacional de Pesquisa de Arroz e Feijão (CNPAF), Universidade Federal de Lavras (UFLA) and Universidade Federal de Viçosa (UFV), from 1974/75 to 1994/95. Results of the comparative trials of upland rice cultivars and lines conducted over the above quoted period were utilized. Because of irregular rainfall distribuition and the distinctive response of different cycles to climatic conditions, the option was to divide them into two groups, one encompassing the early genotypes and the other those of medium cycle. The achieved result showed that an average genetic gain of 1.26% and 3.37% for the early group and medium cycle, respectively, occurred. In addition, it was found that the early group statistically outyielded (P £ 0.01) as to grains the medium cycle group, denoting that in Minas Gerais the short cycle cultivars should be preferred

Progresso genético do melhoramento de arroz de terras altas no período de 1950 a 2001

The objective of this study was to quantify the genetic progress obtained by the genetic improvement of upland rice from 1950 to 2001. Four field experiments were conducted in the sites: Airport and Agronomy, in Viçosa, MG; in the farms Capivara and Palmital, in Santo Antônio de Goiás, GO, and Goianira, GO, respectively. The experiments were installed in a randomized block design, with three replications. Twenty-five cultivars planted in the period from 1950 to 2001 were assessed. Data of grain yield, plant height and days to flowering were collected and analyzed. In order to get the most accurate estimate of the genetic gain, the plants were separated in the groups of early and late cultivars. To estimate the genetic progress, a linear regression of the cultivar means per decade of use was performed. Genetic gains for grain yield were 0.3 and 2.09% per year in the early and late groups, respectively. Over the evaluated period, the mean plant height of the cultivars was reduced by 21 cm in the early group, and 38 cm in the late group. There was mean increase of ten days in the cycle of the early cultivar group and a decrease of 13 days of the late group.O objetivo deste trabalho foi quantificar o progresso genético obtido pelo melhoramento genético na cultura do arroz de terras altas, no período de 1950 a 2001. Foram feitos quatro experimentos de campo, nas localidades: Aeroporto e Agronomia, em Viçosa, MG; e nas Fazendas Capivara e Palmital, em Santo Antônio de Goiás, GO, e Goianira, GO, respectivamente. Os experimentos foram realizados no delineamento de blocos ao acaso, com três repetições. Avaliaram-se 25 cultivares, desenvolvidas no período de 1950 a 2001. Foram coletados e analisados os dados referentes à produtividade de grãos, altura das plantas e dias para a floração. A fim de se obter estimativa mais precisa do ganho genético, optou-se por dividir as cultivares nos grupos precoce e tardio. Para a obtenção da estimativa do progresso genético, foi realizada a regressão linear das médias das cultivares por década de lançamento. Os ganhos genéticos para a produtividade de grãos foram de 0,3 e 2,09% ao ano, nos grupos precoce e tardio, respectivamente. A altura média das plantas das cultivares reduziu-se em 21 cm no grupo precoce e em 38 cm no tardio, no período avaliado. Houve acréscimo médio de dez dias no ciclo, no grupo de cultivares precoce, e decréscimo de 13 dias no grupo tardio