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RESUMONos últimos anos, grande ênfase tem sido dada ao uso de fungicidas para o manejo de doenças foliares na cultura do milho no Brasil. Esse trabalho teve como objetivo a realização de uma análise da viabilidade técnica e econômica da aplicação de fungicidas no rendimento de cultivares de milho em diferentes regiões produtoras. Foram conduzidos experimentos para avaliação do efeito da aplicação de fungicidas no rendimento de diferentes cultivares de milho, em três localidades: Sete Lagoas (MG), Londrina (PR) e Rio Verde (GO). Foram consideradas a não aplicação, uma e duas aplicações de fungicidas em cada cultivar. Foram avaliadas a severidade das doenças foliares e o rendimento de cada cultivar. Os resultados de rendimento das cultivares tratadas com fungicidas apresentaram elevada inconsistência em condições de baixa severidade de doenças. Maior frequência de rendimentos positivos e benefício econômico ocorreu quando as aplicações de fungicida foram realizadas em condição de elevada pressão de doença. Mais estudos são necessários para o melhor entendimento do efeito dos fungicidas do grupo das estrobilurinas na fisiologia e na produção de plantas de milho. Palavras-chave: Zea mays, azoxistrobina, efeito fisiológico, piraclostrobina. ABSTRACT Technical and economic feasibility of strobilurin fungicides application on maizeIn recent years, great emphasis has been given to the use of fungicides for managing foliar diseases in corn in Brazil. This study aimed to conduct an analysis of technical and economic feasibility of application of fungicides on maize in different growing regions. Trials were conducted to evaluate the effect of fungicides on the yield of different maize cultivars at three locations: Sete Lagoas (state of Minas Gerais), Londrina (state of Paraná) and Rio Verde (state of Goiás). The effect of one and two fungicide applications on each cultivar was evaluated. For each trial, the difference in mean yield and disease severities between treated and untreated plots for each cultivars was compared. For all trials, yield response of cultivars treated with fungicides was highly inconsistent under low disease severity. A higher frequency of positive yields and economic benefit occurred when fungicide applications were made under conditions of high disease pressure. More studies are needed to better clarify the effect of strobilurin fungicides on the physiology and production of corn plants.

Keywords RESUMOPantoea ananatis . Palavras-chave:

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-This study aims to describe the single-cross, super sweet corn hybrid BRS Vivi, with above-average ear diameter, lightcolored grains and competitiveness with other sweet corn cultivars. BRS Vivi is a contribution to the expansion of the range of available cultivars on the market and the genetic basis of sweet corn in Brazil.

Maize white spot lesions caused by Pantoea ananatis has contributed substantially to yield reduction of maize crops in many countries, including Brazil. The initial symptoms of the disease include watersoaked lesions on the leaves, which later become necrotic and straw-colored. Basic knowledge regarding the biology and the infection mechanisms of this pathogen is lacking. In this study, 15 P. ananatis isolates obtained from maize white spot lesions were examined for their ice nucleation activity (INA). The INAs of individual bacterial isolates was determined by tube nucleation tests. Bacterial isolates were grown on tryptic soy broth medium and an aliquot of 0.1 mL of culture was added to test tubes containing 1 mL of sterile distilled water. The tubes were packed in an ice bath, which had a temperature below -10°C, for approximately 2 min. Instantaneous formation of ice in the tube revealed a positive INA phenotype of the isolate. Only 9 of the 15 studied isolates showed the INA + phenotype. Pathogenicity tests were performed using whole plants and detached leaves. Symptoms were reproduced in both tests, but only for the inoculations using INA + isolates. Electron microscopy allowed visualization of protein vesicles under outer cell wall of isolates characterized as INA + . Key words: INA, vesicle protein, transmission electron microscopy ResumoLesões de mancha branca do milho causadas por Pantoea ananatis contribuiram substancialmente para a redução da produtividade nos cultivos de milho, em muitos países, incluindo o Brasil. Os sintomas iniciais da doença incluem lesões anasarcas nas folhas, que mais tarde tornam-se necróticas e de cor palha. O conhecimento básico sobre a biologia e os mecanismos de infecção deste patógeno são escassos. Neste estudo, 15 isolados de P. ananatis obtidos a partir de lesões da mancha branca do milho foram examinados quanto à sua atividade de nucleação de gelo (INA). A INA de isolados bacterianos individuais foi determinada por testes de nucleação em tubos. Isolados bacterianos foram cultivados em meio de caldo de soja tríptico e uma alíquota de 0,1 mL de cultura foi adicionada à tubos de ensaio contendo 1 mL de água destilada esterelizada. Os tubos foram colados em banho de gelo, o qual continha temperatura inferior a -10 ºC, por aproximadamente 2 min. A formação de gelo instantânea no tubo revelou um fenótipo INA positivo do isolado. Apenas 9 dos 15 isolados estudados apresentaram o fenótipo INA+. Testes de patogenicidade foram realizados com plantas inteiras e folhas destacadas.

Maize white spot, caused by the bacterium Pantoea ananatis, is one of the most detrimental diseases of maize in Brazil and has contributed to significant yield reduction. In this study, P. ananatis isolates were recovered from maize white spot lesions, healthy leaves, corn crop residues and Digitaria horizontalis. All the bacterial isolates were identified and characterized by morphological traits analysis, acid production from sorbitol and glycerol, ice nucleation activity, metabolic fingerprint similarities and molecular analysis by Polymerase Chain Reaction with species-specific primers for P. ananatis (ANAF/ANAR). Results showed that isolates recovered from maize white spot lesions were similar to those isolates collected from other sources. It suggests that corn crop residues, D. horizontalis and healthy leaf surface of the corn plant itself, could be a source of survival for P. ananatis.

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.