Recurrent mass selection for upright plant architecture in common bean

Plant with a more upright architecture offers many advantages to farmers. Recurrent mass selection (RS) programs for carioca type common bean have been implemented for the purpose of obtaining new lines that will generate the high yields that are associated with upright plant archi tecture. This study aimed to assess the efficiency of recurrent mass selection (RS) for upright plant architecture in common bean (Phaseolus vulgaris) and the effect of RS on grain yield and to verify whether or not there is still variability in the population that favors continuing selection programs, using information obtained from progenies evaluated in cycle five (CV) and cycle eight (CVIII) of the RS program. Mass selection for more upright plants was performed visually in the "S0" generation before flowering. Progenies S and Swere evaluated in 2009 (CV) and 2011 (CVIII). Heritability (h²;) and RS progress were estimated using adjusted means. After eight selection cycles, the population subjected to RS still had enough genetic variability to achieve continued success through recurrent selection. The RS progress was 1.62 % per cycle for the growth habit scores and 6.81 % for grain yiel.

Recurrent mass selection for upright plant architecture in common bean

Plant with a more upright architecture offers many advantages to farmers. Recurrent mass selection (RS) programs for carioca type common bean have been implemented for the purpose of obtaining new lines that will generate the high yields that are associated with upright plant archi tecture. This study aimed to assess the efficiency of recurrent mass selection (RS) for upright plant architecture in common bean (Phaseolus vulgaris) and the effect of RS on grain yield and to verify whether or not there is still variability in the population that favors continuing selection programs, using information obtained from progenies evaluated in cycle five (CV) and cycle eight (CVIII) of the RS program. Mass selection for more upright plants was performed visually in the "S0" generation before flowering. Progenies S and Swere evaluated in 2009 (CV) and 2011 (CVIII). Heritability (h²;) and RS progress were estimated using adjusted means. After eight selection cycles, the population subjected to RS still had enough genetic variability to achieve continued success through recurrent selection. The RS progress was 1.62 % per cycle for the growth habit scores and 6.81 % for grain yiel.(AU)

Genetic control of the angular leaf spot reaction in common bean leaves and pods

Information about genetic control of plant reaction to pathogens is essential in plant breeding programs focusing resistance. This study aimed to obtain information about genetic control of the angular leaf spot reaction in leaves and pods from common bean (Phaseolus vulgaris L.) line ESAL 686. This line was crossed with cultivars Jalo EEP 558 (resistant), Cornell 49-242 (resistant) and Carioca MG (susceptible). Generations F1, F2 and backcrosses (BC11 and BC21) were obtained. In the dry season (2009), parents and respective populations were evaluated for angular leaf spot reaction under field conditions. Disease severity was evaluated on leaves and pods using diagrammatic scales. Severity scores were obtained and mean and variance genetic components were estimated for both. Segregation of F2 generation was analyzed for some crosses. Different genes control angular leaf spot reaction in leaves and pods. Mean and variance components showed predominance of additive effects. Heritability was high, however, was greater on pods than on leaves which indicated that leaf reaction is more influenced by the environment.

Assessment of genetic parameters of degradability in maize grains due to indentation scores

Maize (Zea mays L.) cultivars with dent grains present higher starch and dry matter ruminal degradability than those with flint grains. This study aimed to assess genetic parameters of degradability in maize grains of different textures and to verify whether there is an association between grain indentation score and ruminal dry matter (RDM) degradability. The evaluated progenies were obtained from the cross between the varieties Cristal (flint) and Cunha (dent), previously selected for grain hardness. Progenies were evaluated for an indentation score using a visual grading scale ranging from 1 (flint) to 5 (dent). To assess the RDM degradability, 5 g were cut into halves, weighed (five grams), stored in bags made of 100% "failet" cloth and incubated for 24 h in the rumen of three ruminally cannulated cows. There was genetic variability for RDM degradability and heritability was 46%, indicating the possibility of success using a selection. There was no association between indentation score and RDM degradability percentage; thus, visual evaluation not always reflects grain hardness per se since it indicates the pericarp aspect but not the endosperm constitution.

Cultivares de milho (Zea mays L.) com grãos do tipo dentado possuem maior porcentagem de amido e degradabilidade ruminal da matéria seca do que os com grãos do tipo duro. Estimaram-se parâmetros genéticos da degradabilidade de grãos de milho com diferentes texturas e verificou-se se ocorre associação entre o escore de identação dos grãos visualmente avaliados e a degradabilidade in situ da matéria seca (DISMS). Foram avaliadas progênies oriundas do cruzamento entre a variedade Cristal, de grãos duros, e a variedade Cunha de grãos dentados, previamente selecionadas para a dureza dos grãos. As progênies foram avaliadas com relação ao escore de identação por meio de uma escala visual de notas variando de 1 (duro) a 5 (mole). Para a avaliação da DISMS os grãos foram cortados ao meio, pesados 5 g colocados em saquinhos de tecido "failet" e incubados no rúmen, por 24 h, em três vacas portadoras de cânula ruminal. Há variabilidade genética para a DISMS, com herdabilidade de 46%, indicando ser possível o sucesso com a seleção. Não há associação entre o escore de identação e a porcentagem de DISMS. Assim, a avaliação visual nem sempre reflete a dureza per se dos grãos, pois o que se vê é o aspecto do pericarpo e não a constituição do endosperma.

Assessment of genetic parameters of degradability in maize grains due to indentation scores

Maize (Zea mays L.) cultivars with dent grains present higher starch and dry matter ruminal degradability than those with flint grains. This study aimed to assess genetic parameters of degradability in maize grains of different textures and to verify whether there is an association between grain indentation score and ruminal dry matter (RDM) degradability. The evaluated progenies were obtained from the cross between the varieties Cristal (flint) and Cunha (dent), previously selected for grain hardness. Progenies were evaluated for an indentation score using a visual grading scale ranging from 1 (flint) to 5 (dent). To assess the RDM degradability, 5 g were cut into halves, weighed (five grams), stored in bags made of 100% "failet" cloth and incubated for 24 h in the rumen of three ruminally cannulated cows. There was genetic variability for RDM degradability and heritability was 46%, indicating the possibility of success using a selection. There was no association between indentation score and RDM degradability percentage; thus, visual evaluation not always reflects grain hardness per se since it indicates the pericarp aspect but not the endosperm constitution.

Cultivares de milho (Zea mays L.) com grãos do tipo dentado possuem maior porcentagem de amido e degradabilidade ruminal da matéria seca do que os com grãos do tipo duro. Estimaram-se parâmetros genéticos da degradabilidade de grãos de milho com diferentes texturas e verificou-se se ocorre associação entre o escore de identação dos grãos visualmente avaliados e a degradabilidade in situ da matéria seca (DISMS). Foram avaliadas progênies oriundas do cruzamento entre a variedade Cristal, de grãos duros, e a variedade Cunha de grãos dentados, previamente selecionadas para a dureza dos grãos. As progênies foram avaliadas com relação ao escore de identação por meio de uma escala visual de notas variando de 1 (duro) a 5 (mole). Para a avaliação da DISMS os grãos foram cortados ao meio, pesados 5 g colocados em saquinhos de tecido "failet" e incubados no rúmen, por 24 h, em três vacas portadoras de cânula ruminal. Há variabilidade genética para a DISMS, com herdabilidade de 46%, indicando ser possível o sucesso com a seleção. Não há associação entre o escore de identação e a porcentagem de DISMS. Assim, a avaliação visual nem sempre reflete a dureza per se dos grãos, pois o que se vê é o aspecto do pericarpo e não a constituição do endosperma.

Genetic control of the angular leaf spot reaction in common bean leaves and pods

Information about genetic control of plant reaction to pathogens is essential in plant breeding programs focusing resistance. This study aimed to obtain information about genetic control of the angular leaf spot reaction in leaves and pods from common bean (Phaseolus vulgaris L.) line ESAL 686. This line was crossed with cultivars Jalo EEP 558 (resistant), Cornell 49-242 (resistant) and Carioca MG (susceptible). Generations F1, F2 and backcrosses (BC11 and BC21) were obtained. In the dry season (2009), parents and respective populations were evaluated for angular leaf spot reaction under field conditions. Disease severity was evaluated on leaves and pods using diagrammatic scales. Severity scores were obtained and mean and variance genetic components were estimated for both. Segregation of F2 generation was analyzed for some crosses. Different genes control angular leaf spot reaction in leaves and pods. Mean and variance components showed predominance of additive effects. Heritability was high, however, was greater on pods than on leaves which indicated that leaf reaction is more influenced by the environment.

Inheritance of resistance to Fusarium oxysporum f. sp. phaseoli Brazilian race 2 in common bean

Aiming to obtain information concerning the genetic control of the resistance of the bean (Phaseolus vulgaris L.) to the fungus Fusarium oxysporum f. sp. phaseoli, six crosses involving three resistant lines (Carioca MG, Esal 583 and Esal 566) and four susceptible to the fungus (Carioca, CNFC 10443, Uirapuru and Esal 522) were developed. The parental lines, the controls (Carioca MG and Carioca) and the F1, F2 and F3 generations were evaluated for reaction to Fusarium. For inoculation, root cuttings were immersed in a spore suspension. The evaluations were performed at 21 days after inoculation, by scale of notes ranging from 1.0, to 9.0 and genetic and phenotypic parameters were estimated. The heritability in the narrow sense ranged from 0.34 to 0.42 and in the broad sense of 0.76 to 0.97, showing that selection should be easy, since efficient inoculation and selection methods are used. The average degree of dominance was around 1.0 indicating the presence of dominance in the control of the character, although additive effects are also expressive.

Com o objetivo de obter informações a respeito do controle genético da resistência do feijoeiro (Phaseolus vulgaris L.) ao fungo Fusarium oxysporum f. sp. phaseoli, foram realizados seis cruzamentos envolvendo três linhagens resistentes (Carioca MG, ESAL 583 e ESAL 566) e quatro suscetíveis ao fungo (Carioca, CNFC 10443, Uirapuru e ESAL 522). As plantas dos genitores, das testemunhas (Carioca MG e Carioca) e das gerações F1, F2 e F3 foram avaliadas quanto à reação à murcha-de-fusarium utilizando a metodologia de inoculação de imersão de raízes na suspensão de esporos, com o corte do sistema radicular. As avaliações foram realizadas aos 21 dias após a inoculação, por meio de escala de notas variando de 1,0 (plantas sem sintomas) a 9,0 (plantas mortas). Com os dados obtidos, foram estimados parâmetros genéticos e fenotípicos. A herdabilidade no sentido restrito variou de 0,34 a 0,42 e no sentido amplo de 0,76 a 0,97, podendo considerar o caráter como de fácil seleção, desde que se adotem critérios eficientes de inoculação e avaliação das plantas. O grau médio de dominância foi próximo de 1,0 evidenciando a presença de dominância no controle do caráter, embora a presença de efeitos aditivos também seja expressiva.

Stability of combining ability effects in maize hybrids

General and specific combining ability effects are important indicators in a maize (Zea mays L.) breeding program aiming hybrid development. The objectives of the present study were to estimate the general (GCA) and specific combining abilities (SCA) effects of commercial maize hybrids using a complete diallel scheme and to assess the stabilities of these estimates. Fifty-five entries were assessed; ten commercial single-crosses and all possible double-crosses. The experiments were carried out in 12 environments in the 2005/06 growing season. A randomized complete block design was used with three replications per environment. Ear yield was evaluated, corrected to 13% of moisture content. The combined diallel analysis involving all environments was performed and the stability of general and specific combining ability effects was investigated. The underlying nonparametric statistics evaluated the contribution of each effect to the genotype by environment interaction. Non-additive effects were more important for this set of hybrids than the additive effects. It was possible to select parents with high stability for combining ability and with high GCA.

Os efeitos da capacidade geral (CGC) e específica de combinação (CEC) são indicadores importantes em um programa de melhoramento milho (Zea mays L.) visando a obtenção de híbridos. Os objetivos do presente trabalho foram estimar os efeitos da capacidade geral e específica de combinação de híbridos comerciais de milho e avaliar a estabilidade das estimativas desses parâmetros. Para isso foram avaliados 55 tratamentos, sendo dez híbridos simples comerciais e os 45 híbridos duplos possíveis. Os experimentos foram conduzidos em 12 ambientes no ano agrícola de 2005/06. O delineamento empregado foi o de blocos casualizados com três repetições por ambiente, e o caráter avaliado foi o peso de espigas corrigido para 13% de umidade. Procedeu-se à análise dialélica conjunta envolvendo todos os ambientes e realizou-se o estudo da estabilidade dos efeitos da capacidade geral e específica de combinação, adotando-se a estatística não-paramétrica por meio da soma de postos. Os efeitos não aditivos foram mais importantes que os efeitos aditivos para o desempenho desse conjunto de híbridos. É possível selecionar genitores com alta estabilidade para a capacidade de combinação e com CGC de elevada magnitude.

Stability of combining ability effects in maize hybrids

General and specific combining ability effects are important indicators in a maize (Zea mays L.) breeding program aiming hybrid development. The objectives of the present study were to estimate the general (GCA) and specific combining abilities (SCA) effects of commercial maize hybrids using a complete diallel scheme and to assess the stabilities of these estimates. Fifty-five entries were assessed; ten commercial single-crosses and all possible double-crosses. The experiments were carried out in 12 environments in the 2005/06 growing season. A randomized complete block design was used with three replications per environment. Ear yield was evaluated, corrected to 13% of moisture content. The combined diallel analysis involving all environments was performed and the stability of general and specific combining ability effects was investigated. The underlying nonparametric statistics evaluated the contribution of each effect to the genotype by environment interaction. Non-additive effects were more important for this set of hybrids than the additive effects. It was possible to select parents with high stability for combining ability and with high GCA.

Os efeitos da capacidade geral (CGC) e específica de combinação (CEC) são indicadores importantes em um programa de melhoramento milho (Zea mays L.) visando a obtenção de híbridos. Os objetivos do presente trabalho foram estimar os efeitos da capacidade geral e específica de combinação de híbridos comerciais de milho e avaliar a estabilidade das estimativas desses parâmetros. Para isso foram avaliados 55 tratamentos, sendo dez híbridos simples comerciais e os 45 híbridos duplos possíveis. Os experimentos foram conduzidos em 12 ambientes no ano agrícola de 2005/06. O delineamento empregado foi o de blocos casualizados com três repetições por ambiente, e o caráter avaliado foi o peso de espigas corrigido para 13% de umidade. Procedeu-se à análise dialélica conjunta envolvendo todos os ambientes e realizou-se o estudo da estabilidade dos efeitos da capacidade geral e específica de combinação, adotando-se a estatística não-paramétrica por meio da soma de postos. Os efeitos não aditivos foram mais importantes que os efeitos aditivos para o desempenho desse conjunto de híbridos. É possível selecionar genitores com alta estabilidade para a capacidade de combinação e com CGC de elevada magnitude.

Inheritance of resistance to Fusarium oxysporum f. sp. phaseoli Brazilian race 2 in common bean

Aiming to obtain information concerning the genetic control of the resistance of the bean (Phaseolus vulgaris L.) to the fungus Fusarium oxysporum f. sp. phaseoli, six crosses involving three resistant lines (Carioca MG, Esal 583 and Esal 566) and four susceptible to the fungus (Carioca, CNFC 10443, Uirapuru and Esal 522) were developed. The parental lines, the controls (Carioca MG and Carioca) and the F1, F2 and F3 generations were evaluated for reaction to Fusarium. For inoculation, root cuttings were immersed in a spore suspension. The evaluations were performed at 21 days after inoculation, by scale of notes ranging from 1.0, to 9.0 and genetic and phenotypic parameters were estimated. The heritability in the narrow sense ranged from 0.34 to 0.42 and in the broad sense of 0.76 to 0.97, showing that selection should be easy, since efficient inoculation and selection methods are used. The average degree of dominance was around 1.0 indicating the presence of dominance in the control of the character, although additive effects are also expressive.

Com o objetivo de obter informações a respeito do controle genético da resistência do feijoeiro (Phaseolus vulgaris L.) ao fungo Fusarium oxysporum f. sp. phaseoli, foram realizados seis cruzamentos envolvendo três linhagens resistentes (Carioca MG, ESAL 583 e ESAL 566) e quatro suscetíveis ao fungo (Carioca, CNFC 10443, Uirapuru e ESAL 522). As plantas dos genitores, das testemunhas (Carioca MG e Carioca) e das gerações F1, F2 e F3 foram avaliadas quanto à reação à murcha-de-fusarium utilizando a metodologia de inoculação de imersão de raízes na suspensão de esporos, com o corte do sistema radicular. As avaliações foram realizadas aos 21 dias após a inoculação, por meio de escala de notas variando de 1,0 (plantas sem sintomas) a 9,0 (plantas mortas). Com os dados obtidos, foram estimados parâmetros genéticos e fenotípicos. A herdabilidade no sentido restrito variou de 0,34 a 0,42 e no sentido amplo de 0,76 a 0,97, podendo considerar o caráter como de fácil seleção, desde que se adotem critérios eficientes de inoculação e avaliação das plantas. O grau médio de dominância foi próximo de 1,0 evidenciando a presença de dominância no controle do caráter, embora a presença de efeitos aditivos também seja expressiva.

Using genealogy to improve selection efficiency of pedigree method

In the pedigree method of conducting an autogamous population of segregating plants, the genealogy of the progenies is registered. Although labor-intensive, these data are rarely used. One possibility of exploiting this information is to improve selection efficiency using BLUP (Best Linear Unbiased Prediction). In this study BLUP with genealogy inclusion was compared to the mean in the progenies evaluation conducted by the pedigree method. Progenies of crosses of the common bean lines BRS MG Talismã and BRS Valente in F4:6 and F4:7 were used. The 256 F4:6 progenies were sown in February 2005, in southeast of Brazil, in a 16 FONT FACE=Symbol>´ /FONT> 16 simple lattice design. The grain yield data were subjected to BLUP analysis with inclusion of genealogy. Based on this analysis and the mean, the 30 progenies with best and worst performance were selected. These 60 F4:7 progenies were classified in relation to the origin, i.e., selected by BLUP, mean, or BLUP and mean and coincident results were obtained. In the selection for best performance, the efficiency of BLUP was 2.4% higher than the mean. In the selection for the opposite extreme, BLUP analysis was however not advantageous. The progenies FONT FACE=Symbol>´ /FONT> environments interaction indicates the need for an evaluation of the progenies in different environments before beginning selection.

No método do pedigree de condução de população segregante de plantas autógamas, é anotado a genealogia das progênies. Contudo, normalmente essa informação embora trabalhosa, não é utilizada. Uma das opções é usar esta informação para melhorar a eficiência da seleção empregando o BLUP (Best Linear Unbiased Prediction). Nesse trabalho, foi comparado BLUP com a inclusão de genealogia em relação à média na avaliação de progênies conduzidas pelo método genealógico. Para isto foram utilizadas progênies F4:6 e F4:7 do cruzamento entre as linhagens de feijão BRS MG Talismã e BRS Valente. As 256 progênies F4:6 foram semeadas em fevereiro de 2005, no sudeste do Brasil, no delineamento látice simples 16 FONT FACE=Symbol>´ /FONT> 16. Os dados de produtividade de grãos foram submetidos à análise do BLUP com inclusão da genealogia. A partir dessa análise, e considerando a média, foram selecionadas as 30 progênies com melhor e pior desempenho. Essas 60 progênies F4:7 foram novamente avaliadas e verificada a coincidência na classificação em função da origem, isto é, selecionadas pelo BLUP, média ou BLUP e média. Constatou-se que na seleção efetuada para melhor desempenho o BLUP apresentou eficiência 2,4% acima da obtida com a média, contudo, na seleção efetuada no extremo oposto, não houve vantagem da análise com BLUP. A ocorrência de interação progenies FONT FACE=Symbol>´ /FONT> ambientes evidencia a necessidade de se realizar a avaliação das progênies em alguns ambientes antes de se proceder à seleção.

Using genealogy to improve selection efficiency of pedigree method

In the pedigree method of conducting an autogamous population of segregating plants, the genealogy of the progenies is registered. Although labor-intensive, these data are rarely used. One possibility of exploiting this information is to improve selection efficiency using BLUP (Best Linear Unbiased Prediction). In this study BLUP with genealogy inclusion was compared to the mean in the progenies evaluation conducted by the pedigree method. Progenies of crosses of the common bean lines BRS MG Talismã and BRS Valente in F4:6 and F4:7 were used. The 256 F4:6 progenies were sown in February 2005, in southeast of Brazil, in a 16 FONT FACE=Symbol>´ /FONT> 16 simple lattice design. The grain yield data were subjected to BLUP analysis with inclusion of genealogy. Based on this analysis and the mean, the 30 progenies with best and worst performance were selected. These 60 F4:7 progenies were classified in relation to the origin, i.e., selected by BLUP, mean, or BLUP and mean and coincident results were obtained. In the selection for best performance, the efficiency of BLUP was 2.4% higher than the mean. In the selection for the opposite extreme, BLUP analysis was however not advantageous. The progenies FONT FACE=Symbol>´ /FONT> environments interaction indicates the need for an evaluation of the progenies in different environments before beginning selection.

No método do pedigree de condução de população segregante de plantas autógamas, é anotado a genealogia das progênies. Contudo, normalmente essa informação embora trabalhosa, não é utilizada. Uma das opções é usar esta informação para melhorar a eficiência da seleção empregando o BLUP (Best Linear Unbiased Prediction). Nesse trabalho, foi comparado BLUP com a inclusão de genealogia em relação à média na avaliação de progênies conduzidas pelo método genealógico. Para isto foram utilizadas progênies F4:6 e F4:7 do cruzamento entre as linhagens de feijão BRS MG Talismã e BRS Valente. As 256 progênies F4:6 foram semeadas em fevereiro de 2005, no sudeste do Brasil, no delineamento látice simples 16 FONT FACE=Symbol>´ /FONT> 16. Os dados de produtividade de grãos foram submetidos à análise do BLUP com inclusão da genealogia. A partir dessa análise, e considerando a média, foram selecionadas as 30 progênies com melhor e pior desempenho. Essas 60 progênies F4:7 foram novamente avaliadas e verificada a coincidência na classificação em função da origem, isto é, selecionadas pelo BLUP, média ou BLUP e média. Constatou-se que na seleção efetuada para melhor desempenho o BLUP apresentou eficiência 2,4% acima da obtida com a média, contudo, na seleção efetuada no extremo oposto, não houve vantagem da análise com BLUP. A ocorrência de interação progenies FONT FACE=Symbol>´ /FONT> ambientes evidencia a necessidade de se realizar a avaliação das progênies em alguns ambientes antes de se proceder à seleção.

Resposta diferencial de linhagens de feijoeiro ao nitrogênio

It was evaluated 100 breeding lines of common bean in the presence and absence of N in cover in four conditions aiming at identifing the lines of beans which would be tolerant to nitrogen (N) stress and/or also responsive to this nutrient. In each condition there were two distinct experiments with and without N, in a 10 x 10 triple lattice design, being the plot constituted by a line with three meters of length. It was estimated the index of efficiency of nitrogen utilization, through the average grains yield. The obtained yield with N was 12% above the one without N, in the average of the four conditions. By decomposing the effect of levels for each line, in 77% of them there was no answer to the nitrogen fertilization in cover. This, only 22 lines positively responded to nitrogen fertilization and among them the efficiency of N utilization ranged from 11.3 to 18.3kg of grains per kg of applied N.

Visando à identificação de linhagens de feijão que sejam tolerantes ao estresse de nitrogênio (N) e que também apresentem resposta positiva a esse nutriente, foram avaliadas 100 linhagens em presença e ausência de N em cobertura, em quatro ambientes. Em cada ambiente, foram dois experimentos distintos com e sem N, no delineamento látice triplo 10x10, sendo a parcela constituída de uma linha de três metros de comprimento. Utilizando a produtividade média de grãos, foi estimado o índice de eficiência de utilização de nitrogênio. Na média dos quatro ambientes, a produtividade de grãos obtida com N foi 12% acima da obtida sem N. Decompondo o efeito de níveis para cada linhagem, em 77% delas não houve resposta à adubação nitrogenada em cobertura. Assim, apenas 22 linhagens responderam positivamente à adubação nitrogenada e, entre elas, a eficiência na utilização de N variou de 11,3 a 18,3kg de grãos por kg de N aplicado.

Resposta diferencial de linhagens de feijoeiro ao nitrogênio

It was evaluated 100 breeding lines of common bean in the presence and absence of N in cover in four conditions aiming at identifing the lines of beans which would be tolerant to nitrogen (N) stress and/or also responsive to this nutrient. In each condition there were two distinct experiments with and without N, in a 10 x 10 triple lattice design, being the plot constituted by a line with three meters of length. It was estimated the index of efficiency of nitrogen utilization, through the average grains yield. The obtained yield with N was 12% above the one without N, in the average of the four conditions. By decomposing the effect of levels for each line, in 77% of them there was no answer to the nitrogen fertilization in cover. This, only 22 lines positively responded to nitrogen fertilization and among them the efficiency of N utilization ranged from 11.3 to 18.3kg of grains per kg of applied N.

Visando à identificação de linhagens de feijão que sejam tolerantes ao estresse de nitrogênio (N) e que também apresentem resposta positiva a esse nutriente, foram avaliadas 100 linhagens em presença e ausência de N em cobertura, em quatro ambientes. Em cada ambiente, foram dois experimentos distintos com e sem N, no delineamento látice triplo 10x10, sendo a parcela constituída de uma linha de três metros de comprimento. Utilizando a produtividade média de grãos, foi estimado o índice de eficiência de utilização de nitrogênio. Na média dos quatro ambientes, a produtividade de grãos obtida com N foi 12% acima da obtida sem N. Decompondo o efeito de níveis para cada linhagem, em 77% delas não houve resposta à adubação nitrogenada em cobertura. Assim, apenas 22 linhagens responderam positivamente à adubação nitrogenada e, entre elas, a eficiência na utilização de N variou de 11,3 a 18,3kg de grãos por kg de N aplicado.