-The objective of this work was to assess the effect of successive selection cycles on leaf plasticity of 'Saracura' maize BRS-4154 under periodical flooding in field conditions. Soil flooding started at the six-leaf stage with the application of a 20-cm depth water layer three times a week. At flowering, samples of leaves were collected and fixed. Paradermic and transverse sections were observed under photonic microscope. Several changes were observed throughout the selection cycles, such as modifications in the number and size of the stomata, higher amount of vascular bundles and the resulting decrease of the distance between them, smaller diameter of the metaxylem, decrease of cuticle and epidermis thickness, decrease of number and size of bulliform cells, increase of phloem thickness, smaller sclerenchyma area. Therefore, the successive selection cycles of 'Saracura' maize resulted in changes in the leaf anatomy, which might be favorable to the plant's tolerance to the intermittent flooding of the soil.Index terms: Zea mays, hypoxia, leaf anatomy, tolerance to flooding. Plasticidade foliar nos sucessivos ciclos de seleção do milho'Saracura' em resposta ao alagamento intermitente do soloResumo -O objetivo deste trabalho foi avaliar o efeito de sucessivos ciclos de seleção na plasticidade foliar do milho 'Saracura' BRS-4154 sob alagamento intermitente do solo em condições de campo. O alagamento do solo iniciou-se no estádio de seis folhas com a aplicação de uma lâmina de 20 cm de água três vezes por semana. No florescimento, foram coletadas e fixadas amostras das folhas. Secções paradérmicas e transversais de amostras foram observadas em microscópio fotônico. Várias modificações foram observadas durante os ciclos de seleção, como o número e o tamanho dos estômatos, a maior quantidade de feixes vasculares e a consequente diminuição da distância entre eles, o metaxilema com diâmetros menores, a diminuição da espessura da cutícula e da epiderme, a diminuição no número e tamanho das células buliformes, o aumento da espessura do floema e a menor área de esclerênquima. Os sucessivos ciclos de seleção do milho 'Saracura', portanto, levaram a mudanças na anatomia foliar, as quais podem ser favoráveis à tolerância da planta ao alagamento intermitente do solo.Termos para indexação: Zea mays, hipoxia, anatomia foliar, tolerância ao alagamento.
A leaf spot disease in maize has been reported throughout all corn producing areas in Brazil, and its incidence and severity have increased significantly. Initial symptoms are characterized by the development of dark green water-soaked leaf spots, which later turn into straw-colored necrotic lesions. Some authors associated the symptoms of this disease to those of the disease Phaeosphaeria Leaf Spot caused by fungus Phaeosphaeria maydis (f. imperf. Phyllosticta sp.). However, we reported in previous works the involvement of a bacterium, the Pantoea ananas (syn. Erwinia ananas) as the initiator agent this disease. The aim of this work was to evaluate the behavior of corn genotypes when inoculated with P. ananas in the greenhouse. The results reinforced those previously obtained that showed the role of the bacterium as the initiator agent of the disease.
RESUMOO objetivo deste estudo foi determinar através das estimativas de parâmetros genéticos o potencial de um sintético de milho de grãos duros e de ciclo semiprecoce, para a formação de híbridos e/ou melhoramento intrapopulacional. Foram utilizadas 142 progênies endogâmicas S 2 do Sin EEL Flint, em cruzamentos topcrosses com um Sintético heteroticamente contrastante. Essas progênies topcrosses foram avaliadas utilizando-se o delineamento em látice simples 12 x 12, e em dois locais de teste. Os maiores valores médios para PED foram observados para os topcrosses n.º 101 (12069kg ha -1 ) e n o 72 (11068Kg ha -1 ), tendo o primeiro apresentado comportamento específico para Londrina, e o segunda demonstrado comportamento superior nos dois ambientes. Os valores das estimativas dos parâmetros estudados foram semelhantes aos encontrados em alguns estudos conduzidos em condições tropicais. O grupo de progênies S 2 da Sin EEL Flint conduziu a valores médios de , CVg e h 2 similares aos encontrados na literatura para outros genótipos. Observa-se que esse Sintético possui suficiente variabilidade genética e potencial para extração de linhagens para formação de híbridos e como germoplasma em programas de melhoramento.Palavras-chave: parâmetro genético interpopulacionais, produção, Zea mays L. ABSTRACTThe objective of this study was to determine the genetic potential of a semi-early maize synthetic with flint type kernel (Sin EEL Flint). The estimation of genetic parameters was obtained with S 2 progenies, and the performance of the progenies in hybrid combinations were evaluated. One hundred fourty-two S 2 progenies of Sin EEL Flint were used. They were obtained by top crossings with a contrasting heterotic synthetic of dent type kernel. These topcross progenies were tested in a lattice design 12 x 12 with two replications in two locations, Sete Lagoas and Londrina. The selected topcross nº 101, with specific adaptation for Londrina. and n o 72, being adapted to both locations, were the best yieldings (PED) with 12069Kg ha -1 and 11068Kg ha -1 , respectively. Values of the estimated parameters for , CVg and h 2 were similar to those found in other studies conducted in tropical conditions. It was observed that this synthetic has enough genetic and potential variability to inbred line extraction for hybrid production and to be used as germoplasm source in breeding programs.
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