Potencial de melhoramento e divergência genética de cultivares de milho-pipoca

The objective of this paper was to evaluate the potential of breeding and genetic divergence in nine tropical popcorn cultivars. The genetic divergence was estimated using multivariate analysis techniques and the cultivars were grouped based in Mahalanobis' generalized distance (MGD), using Tocher's optimization and graphic dispersion. The best cultivars concerning the yield grain above 3 ton/ha were CMS 43, IAC 112, Viçosa, CMS 42 and Branco, and to popping expansion above 24 (v/v) were IAC 112, RS 20 and Zélia. The estimates of MGD indicated the pairs genetically more distant (RS 20, Beija-flor) and (Rosa-claro, RS 20) as well as pairs genetically more similar (IAC 112, Viçosa) and (Branco, CMS 42). Tree or four genetic divergences groups were formed depending on the method. To popcorn breeding, cultivars with best potential are RS 20, Zélia, IAC 112, and Beija-flor. The cultivars show genetic divergence.O objetivo deste trabalho foi avaliar o potencial de melhoramento e a divergência genética de nove cultivares tropicais de milho-pipoca. A divergência genética foi estimada por meio da técnica de análise multivariada e as cultivares foram agrupadas com base na distância generalizada de Mahalanobis (DGM), utilizando o método de otimização de Tocher e a dispersão gráfica. Com produtividade de grãos acima de 3 t/ha, destacaram-se as cultivares CMS 43, IAC 112, Viçosa, CMS 42 e Branco, e com índices de capacidade de expansão acima de 24 (v/v), as cultivares IAC 112, RS 20 e Zélia. As estimativas da DGM indicaram (RS 20 e Beija-flor) e (Rosa-claro e RS 20) os pares de cultivares mais distantes geneticamente, e (IAC 112 e Viçosa) e (Branco e CMS 42), os pares mais similares. Foram identificados três ou quatro grupos divergentes dependendo do método de agrupamento. Para o melhoramento de milho-pipoca, as cultivares com maiores potenciais são RS 20, Zélia, IAC 112 e Beija-flor. As cultivares apresentam divergência genética

Maize improvement for nitrogen stress

O presente trabalho teve por objetivo geral identificar estratégias de melhoramento de milho para estresse de nitrogênio e os seguintes objetivos específicos: determinar as doses de nitrogênio que caracterizam ambientes de adequada e de baixa disponibilidade de nitrogênio para a seleção de genótipos de milho; avaliar famílias endogâmicas S1 per se e seus respectivos híbridos top crosses sob estresse de nitrogênio; e avaliar a viabilidade do medidor portátil de clorofila como ferramenta de seleção de genótipos eficientes na utilização de nitrogênio. Para isso foram conduzidos dois conjuntos de experimentos; no primeiro, os cultivares de milho P30F80, DKB 901, BR 201, BR 106, Sol da Manhã e CMS 39 foram classificados quanto à eficiência na utilização e resposta à aplicação de nitrogênio para servirem como testemunhas na avaliação de famílias S1 e de seus híbridos top crosses. O experimento foi instalado em blocos ao acaso, com os tratamentos dispostos no esquema de parcela subdividida com três repetições. As parcelas foram compostas pelas doses de nitrogênio 0, 30, 60, 120 e 200 kg ha-1 e as subparcelas pelos cultivares. Para identificar os cultivares eficientes e responsivos foram utilizadas duas metodologias: uma, com base no coeficiente de regressão da produtividade de grãos, em função das doses; e a outra, com base na definição de que a eficiência é avaliada pela produtividade média do grupo de cultivares em baixo N e a resposta é a diferença entre a produtividade de grãos de um cultivar em baixa e em adequada disponibilidade de N, dividida pela diferença entre as doses de N. No segundo conjunto de experimentos foram avaliadas famílias S1 obtidas de duas populações de milho de polinização aberta, sendo uma considerada eficiente no uso de nitrogênio e a outra considerada de alta resposta ao fertilizante nitrogenado. O comportamento das famílias S1 per se foi avaliado sob condições de adequada e de baixa disponibilidade de N, e o comportamento de seus respectivos híbridos top crosses sob baixa disponibilidade de N. Todos os experimentos foram conduzidos na Estação Experimental do Departame nto de Fitotecnia da Universidade Federal de Viçosa, localizado no município de Coimbra (MG), na safra 2001/2002. As principais conclusões foram: as doses de nitrogênio que discriminam ambientes de baixa e adequada disponibilidade nas condições edafoclimáticas da Estação Experimental de Coimbra (MG) foram 30 e 120 kg ha-1 de N; os cultivares BR 201 e CMS 39 são adequados para o cultivo em ambos ambientes; o cultivar DKB 901 é mais adequado para ambientes de baixa disponibilidade de N; o cultivar P30F80 é adequado para alta disponibilidade de N; o desempenho das famílias endogâmicas S1 não prediz o desempenho dos híbridos top crosses; as famílias endogâmicas S1 manifestaram boa capacidade de combinação com o testador; os híbridos top crosses apresentaram bom desempenho em estresse de baixo nitrogênio, atingindo produtividades superiores às das testemunhas; a leitura do medidor portátil de clorofila pode ser utilizada como critério para eliminar os genótipos menos produtivos antes do florescimento, sendo mais associada à produtividade de grãos no ambiente com baixa disponibilidade de nitrogênio; híbridos obtidos do cruzamento de linhagens oriundas de populações de milho eficientes na utilização e responsivas à aplicação de N podem ser avaliados em condição de adequada disponibilidade desse nutriente.Overall objective of his study was the identification of improvement strategies for maize in relation to nitrogen stress, with the following specific aims: determination of nitrogen doses that characterize adequate environments of low nitrogen availability for the selection of maize genotypes; evaluation of endogamic families S1 per se and their respective top cross hybrids under nitrogen stress; and evaluation of the suitability of the portable chlorophyll meter as instrument for the selection of genotypes efficient at nitrogen utilization. Two sets of experiments were conducted with these purposes; in the first, the maize cultivars P30F80, DKB 901, BR 201, BR 106, Sol da Manhã, and CMS 39 were classified according to their efficiency of N use and their answer to the application of nitrogen as control in the evaluation of S1 families and their top cross hybrids. The experiment was set up in a randomized block design, and the treatments arranged in subplots with three replications. The plots represented nitrogen doses of 0, 30, 60, 120, and 200 kg ha-1, and the subplots the cultivars. Two methodologies were used to define efficient and responsive cultivars: one based on the regression coefficient of grain productivity in relation to the doses; the other based on the definition that efficiency is evaluated by the mean productivity of the cultivar group under low N, and the answer is the difference between the grain productivity of a cultivar under low and under adequate N availability divided by the difference between the N doses. In the second set of experiments, S1 families obtained from two maize populations in open pollination were evaluated, where one was considered efficient at nitrogen utilization and the other considered highl y responsive to nitrogen fertilizer. The behavior of the S1 families per se was evaluated under adequate and low N availability conditions, and the behavior of its respective top cross hybrids under low N availability. All experiments were conducted at the Experimental Station of the Department of Plant Science at the Universidade Federal de Viçosa, in the county of Coimbra, State of Minas Gerais, Brazil, during the harvest of 2001/2002. The following conclusions were drawn: the nitrogen doses that discriminate environments of low and adequate availability under the edaphoclimatic conditions of the Experimental Station of Coimbra were 30 and 120 kg ha-1 N; cultivars BR 201 and CMS 39 are adequate for cultivation in both environments; cultivar DKB 901 is more adequate for environments of low N availability; cultivar P30F80 is adequate for high N availability; the performance of the endogamic S1 families is no prevision for the performance of the top cross hybrids; the endogamic S families presented a good combination capacity with the testcross; the top cross hybrids presented an excellent performance under low nitrogen stress, outstripping the productivity of the control treatments; readings of the portable chlorophyll meter can be used as criteria to eliminate less productive genotypes more associated to grain productivity in environments of low nitrogen availability before flowering; hybrids obtained by crosses with lineages from maize populations efficient at utilization and the response to N application can be evaluated under adequate availability of the nutrient.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Brazilian Society of Plant Breeding. Printed in Brazil Selection of discrepant maize genotypes for nitrogen use efficiency by a chlorophyll meter

ABSTRACT -The objective of the present study was to verify if it is possible t

Determination of leaf sampling techniques to assess the nutritional status of Barbados cherry (

Introduction. Research on the mineral nutrition of Barbados cherry is scarce. Leaf sampling techniques for this crop are unknown. Leaf analysis, associated with the determination of the nutrient availability in the soil, can provide reliable orientation for the establishment of fertilizer programs. For a correct interpretation of the nutritional status, it is important (1) to evaluate the seasonal variation of nutrient contents in the leaves, (2) to determine the appropriate time for leaf sampling and analysis, and (3) to indicate the best part of the plant for determination of the nutritional status. These subjects were the three objectives of this study. Materials and methods. The experiment was conducted from March 1997 to February 1998 in Visconde do Rio Branco, Minas Gerais, Brazil. The dynamics of the elements N, P, K, Ca, Mg, S, Fe, Cu, Zn and Mn were studied in leaves at the apical, median and basal positions of branches located in the upper, median and lower portions of the plant canopy. Results. The minimum variation in the foliar contents occurred at the medium third of the branches located in the upper portion of the canopy. So, these parts are the most appropriate for leaf sampling. Moreover, December was characterized as the appropriate time for leaf sampling. Conclusion. The leaf sampling techniques developed will allow better study of the mineral nutrition of M. emarginata in order to establish reliable fertilizer programs and to improve the yields of this fruit tree

Methods to classify maize cultivars in use efficiency and response to nitrogen

n plant breeding programs that aim to obtain cultivars with nitrogen (N) use efficiency, the focus is on methods of selection and experimental procedures that present low cost, fast response, high repeatability, and can be applied to a large number of cultivars. Thus, the objectives of this study were to classify maize cultivars regarding their use efficiency and response to N in a breeding program, and to validate the methodology with contrasting doses of the nutrient. The experimental design was a randomized block with the treatments arranged in a split-plot scheme with three replicates and five N doses (0, 30, 60, 120 and 200 kg ha-1) in the plots, and six cultivars in subplots. We compared a method examining the efficiency and response (ER) with two contrasting doses of N. After that, the analysis of variance, mean comparison and regression analysis were performed. In conclusion, the method of the use efficiency and response based on two N levels classifies the cultivars in the same way as the regression analysis, and it is appropriate in plant breeding routine. Thus, it is necessary to identify the levels of N required to discriminate maize cultivars in conditions of low and high N availability in plant breeding programs that aim to obtain efficient and responsive cultivars. Moreover, the analysis of the interaction genotype x environment at experiments with contrasting doses is always required, even when the interaction is not significant

Reação de cultivares de milho-pipoca a Helmintosporiose

Avaliou:se a reaÇav de nove populações de milho-pipoca a Exserohilum turricum por meio de infec9ao natural em qualro epocas de semeadura. D delineamento experimental utilizada foi o de blows ao acaso, com Tres repet4oes. Foram realizadas de tries a cinco avaliações em oito plantar por parcels, a partir do florescimento, com intervalo de sete dias. Foi utilizada escala de notas de I a 5, correspondendo as porcentagens de area foliar afetada de 0 e 1U0%, respectivamente. Foi calculada a area abaixo da curva de Progresso da doença e realizada a analise de variancia das notas de severidade da doença. Os cultivares que em todas as semeaduras apresentaram-se nos grupos estatisticos com menor suscetibilidade a helmintosporiose foram SAC 112, CMS 43, CMS 42, Branco, Beija-flor e Rosa Clam, diferindo do cultivar RS 20. No entanto, somente IAC 112 diferiu estatisticamente do cultivar S 20 em todas as épocas de semeadura. Os cultivares CMS 42 e 43 apresentaram-se com menores rea0es a helmintosporiose em relação ao RS 20 somente nas semeaduras realizadas m novembro e dezembro. Os cultivates Beija-flor e Branco apro n se corn menores rearfves a IwJniintospoiiose em relaÇao ao RS 20 somente na semeadura de dmbro Concluiu-se que, quarto a rear* a IIeIInIIItOSpOnOSe, os cultivarec comportaram-se de modo difente, sen+do rye IAC 112; mediaznente ante CMS 43; moderadamente suscetiveis CMS 42, Branco, Beija-flor, Viçosa e Rosa-Claro; e suscetiveis Zélia e RS 2D. A avalia9Ao semanal que melhor discriininou os cultivar+es de milho-pipoca ocorreu aos 21 dias apps o florescimento. A época de semeadura que se mostrou favorável ao desenvolvimento da doenÇa foi outubro.The objective of this work was to evaluate the reaction of nine popcom populations to Exserjohilum turcicum by natural infection in four sowing dates. The trials were arranged in & randomized complete-block design with three replications. Eight plants were evaluated during three to tive seasons, from the flowering stage, in intervals of seven days. The rating scale used ranged from 1 to 5, where ] indicated no disease and 5 indicated a serious infection. The area under the disease progress curve was calculated and the disease severity variance analysis was performed. IAC 112, CMS 43, CMS 42, Branco, Beija-Hor, and Rosa Claro were the most resistant cultivars in every sowing date, differing from RS 20 cultivar. However, only [AC 112 was statistically different of RS 20 in every sowing dates. CMS 42 and CMS 43 showed a lower reaction to E. turcicum than RS 20 only in November and December. Beija-flor and Branco showed a lower reaction to the disease than RS 20 only in December. It was concluded that cultivars have different behaviors: [AC 112 is resistant; CMS 43 is moderately resistant; CMS 42, Branco, Beija-Hor, Viçosa and Rosa Claro are moderately susceptible', and Zélia and RS 20 are susceptible. The best weekly evaluation for popcorn cultivars occurred 21 days and the flowering stage. The most efficimt sowing dates for disease development was in Octoba