RESUMO O míldio é uma doença com alto potencial destrutivo para as lavouras de cebola. Os produtores de cebola têm adensado seus plantios com o objetivo de aumentar a produtividade, o que pode propiciar condições ainda mais favoráveis à doença. O objetivo do trabalho foi estudar o efeito da adubação nitrogenada e da população de plantas na severidade do míldio e produção de biomassa de bulbos sob cultivo superadensado para as condições do Alto Vale do Itajaí – SC. Os tratamentos foram quatro populações de plantas (400, 600, 800 mil e 1,0 milhão de plantas ha-1) submetidas a duas doses de nitrogênio (150 e 200 kg N ha-1). Doses de nitrogênio, de 150 e 200 kg N ha-1, não influenciam a severidade do míldio e a biomassa de bulbos. O aumento populacional de plantas a partir de 600 mil plantas por ha-1 aumenta a severidade do míldio e reduz a biomassa de bulbos.

ABSTRACT Downy mildew is a disease with high destructive potential for onion crops. Onion producers have increased the density of their crops with the aim of rising productivity, which can provide even more favorable conditions for the disease. The aim of this study was to investigate the effect of nitrogen fertilization and plant density on the severity of downy mildew and bulb biomass production under super-dense cultivation for the conditions at Alto Vale do Itajaí – Santa Catarina State, Brazil. Treatments consisted of four plant densities (400, 600, 800 thousand and 1.0 million plants ha-1) receiving two nitrogen levels (150 and 200 kg N ha-1). Nitrogen levels of 150 and 200 kg ha-1 do not influence the severity of downy mildew and the biomass of bulbs. The increase in plant density from 600 thousand plants ha-1 increases the severity of downy mildew and reduces the biomass of bulbs.

ABSTRACT This study investigated the effects of silicon (Si), acibenzolar-S-methyl (ASM), and potassium phosphite (Phi) on the potentiation of rice resistance to infection by Bipolaris oryzae. The treatments included the soil amended with Si (1.25 g of calcium silicate per kg of soil), spraying of plants with ASM (500 mg∙L–1), Phi (5 mL∙L–1), and distilled water (control) 24 h before inoculation with B. oryzae. The treatments Si supply and the spraying of ASM and Phi were effective in reducing the area under brown spot progress curve and the number of lesions per cm2 of leaf. Polyphenoloxidases activity was higher for plants supplied with Si. On plants sprayed with ASM, the activities of polyphenoloxidases, phenylalanine ammonia-lyases, chitinases, and β-1,3-glucanases increased. The spraying of plants with Phi did not increase the activities of the studied defense enzymes. Taken together, the results of this study indicated that brown spot symptoms can be greatly reduced with the use of Si, ASM, and Phi.

AbstractTomato bacterial spot on tomato may be caused by four species of Xanthomonas and among them X. gardneri(Xg) is the most destructive one, especially in areas irrigated using a center pivot system in Minas Gerais state and the midwest region of Brazil. Due to the ineffectiveness of chemical control and the lack of cultivars with high levels of genetic resistance, this study investigated the potential of three antagonists (Streptomyces setonii (UFV618), Bacillus cereus (UFV592) and Serratia marcescens (UFV252)), and the hormone jasmonic acid (JA) as a positive control, to reduce bacterial spot symptoms and to potentiate defense enzymes in the leaves of tomato plants infected by Xg. Tomato seeds were microbiolized with each antagonist, and the soil was drenched with these bacteria. The plants were sprayed with JA 48 h before Xginoculation. The final average severity on the tomato plants was reduced by 29.44, 59.26 and 61.33% in the UFV592, UFV618 and JA treatments, respectively. The UFV618 antagonist was as effective as JA in reducing bacterial spot symptoms on tomatoes, which can be explained by the greater activities of defense enzymes that are commonly involved in host resistance against bacterial diseases. These results suggest that JA and the UFV618 antagonist can be used in the integrated management of bacterial spot on tomatoes.

A murcha-de-fusário, causada por Fusarium oxysporum f.sp. lycopersici (Fol), é uma das mais importantes doenças que afetam a produção de tomate no mundo. Este estudo investigou o potencial de três antagonistas, Streptomyces setonii (UFV 618), Bacillus cereus (UFV 592) e Serratia marcescens (UFV 252), e como controle positivo foi utilizado o hormônio ácido jasmônico (AJ), na redução dos sintomas da murcha-de-fusário e potencialização das enzimas de defesa nos tecidos do caule de plantas de tomateiro infectadas por Fol. Sementes foram microbiolizadas com cada antagonista e o solo também foi encharcado com eles. As plantas foram pulverizadas com AJ 48 horas antes da inoculação Fol. A área abaixo da curva do progresso do índice da murcha-de-fusário (AACPIMF) foi reduzida em 54%, 48%, 47% e 45% para os tratamentos UFV 618, AJ, UFV 592 e UFV 252, respectivamente. Os três antagonistas, e até mesmo a pulverização AJ, foram eficientes na redução dos sintomas da murcha-de-fusário em caules de tomateiro, o que pode ser explicado pela menor concentração de aldeído malônico (uma indicação de danos oxidativos em lípideos nas membranas plasmáticas) e maior atividade de peroxidases, polifenoloxidases, glucanases, quitinases, fenilalanina amônia liases e lipoxigenases, comumente envolvidas na resistência do hospedeiro a doenças fúngicas. Esses resultados apresentam uma nova alternativa que pode ser usada no manejo integrado da murcha-de-fusário em tomateiro.

Fusarium wilt, caused by Fusarium oxysporum f.sp. lycopersici (Fol), is one of the most important diseases that affect tomato yield worldwide. This study investigated the potential of three antagonists, Streptomyces setonii (UFV 618), Bacillus cereus (UFV 592) and Serratia marcescens (UFV 252), and as positive control the hormone jasmonic acid (JA), to reduce Fusarium wilt symptoms and to potentiate the defense enzymes in the stem tissues of tomato plants infected by Fol. The seeds were microbiolized with each antagonist, and the soil was also drenched with them. The plants were sprayed with JA 48 h before Fol inoculation. The area under the Fusarium wilt index progress curve was reduced by 54, 48, 47 and 45% for the UFV 618, JA, UFV 592 and UFV 252 treatments, respectively. The three antagonists, and even the JA spray, efficiently reduced the Fusarium wilt symptoms on the tomato plant stems, which can be explained by the lower malondialdehyde concentration (an indication of oxidative damage to lipids in the plasma membranes) and the greater activities of peroxidases, polyphenoloxidases, glucanases, chitinases, phenylalanine ammonia-lyases and lipoxygenases, which are commonly involved in host resistance against fungal diseases. These results present a novel alternative that can be used in the integrated management of Fusarium wilt on tomatoes.

Considering the importance of bacterial leaf speck (Pseudomonas syringae pv. tomato) in reducing tomato yield and difficulties in disease control, this study investigated the effects of fractions of shells extract of Stryphnodendron adstringens (Sa) and fruit extract of Caesalpinia ferrea (Cf) compared to Acibenzolar-S-Methyl (ASM) on reducing bacterial leaf speck symptoms and on the potentiation of the activities of defense enzymes. The number of lesions per plant (NLP) was significantly lower in plants treated with the ethyl acetate fraction (EAF) of S. adstringens (Sa) and ASM compared to other treatments (EAF of Cf, n-butanol fractions of Sa and Cf, aqueous fractions of Sa and Cf and sterile distilled water). The bacteria were inhibited by the EAF of Sa and EAF of Cf and n-butanol fractions of Sa and Cf according to the bioautography assay. Saponins and tannins were the two major compounds found in these fractions based on the phytochemical analysis. Peroxidase (POX), polyphenoloxidase (PPO), β-1,3-glucanase (GLU) and phenylalanine ammonia-lyase (PAL) activities were determined on the leaves of plants treated with EAF Sa, ASM and sterile distilled water. Both POX and PAL activities were higher at 3 and 6 days after inoculation (dai), while the PPO and GLU activities were higher from 9 to 12 dai. It is suggested that saponins increased tomato resistance to P. s. pv. tomato because no antimicrobial activity against the bacteria was observed. In conclusion, the EAF Sa was very efficient in reducing bacterial leaf speck symptoms in conditions where the POX, PPO, PAL and GLU activities played a pivotal role in increasing tomato resistance to the disease.

This study investigated the effects of acibenzolar-S-methyl (ASM), ethylene (ET) and jasmonic acid (JA) on the resistance of two wheat cultivars (BRS-229 and BR-18) to infection by Pyricularia oryzae. The treatments included spraying plants with ASM (300 mg L-1), ET (0.5 mM), JA (0.1 mM) and distilled water (control) 48 h before inoculation with P. oryzae. Malondialdehyde concentration, an indicative of oxidative damage to the lipids in the leaf cells, was significantly higher for plants sprayed with ASM compared to plants sprayed with JA and ET. Plants sprayed with JA and ET showed reduced values for the number of lesions per cm² of leaf area and area under blast progress curve, but these hormones had no effect on the incubation period and lesion size (in mm). Plants sprayed with JA and ET showed reduce blast symptoms in comparison to plants sprayed with ASM due to greater peroxidase, polyphenoloxidase, chitinase and β-1,3-glucanase activities.

This study aimed to evaluate the effect of silicon (Si) on the resistance of tomato plants (cv. Santa Clara) to bacterial speck, caused by Pseudomonas syringae pv. tomato (Pst). Tomatoes were grown in soil without calcium silicate (control), in soil without calcium silicate and sprayed with Supa Sílica® (2 mL/L) (SS) and in soil with calcium silicate (0.16 g/kg of soil) (CS). The effect of SS on the growth of Pst was evaluated in vitro. There was no significant difference among the treatments for foliar Si concentration and incubation period. No significant differences were observed between the control and CS for the number of lesions per plant (NLP) and bacterial speck severity estimated by the software QUANT. The NLP was significantly reduced with SS spray. There was a negative linear response of in vitro Pst growth to the SS rates. Peroxidase, polyphenoloxidase and glucanase activities were significantly higher for plants sprayed with SS and grown in soil with CS compared to the control treatment. Phenylalanine ammonia-lyase and lypoxygenase activities were significantly higher for plants grown in soil with CS compared to the control. The concentration of malondialdehyde was significantly higher for plants sprayed with SS compared to the control at 0 and 7 dai. The results of this study indicate that the symptoms of bacterial speck are reduced when plants are sprayed with SS, which can be linked to the direct effect of this product against Pst rather than the potentation of host defense responses.

A mancha parda, causada pelo fungo Bipolaris oryzae, é uma das principais doenças da cultura do arroz. Sabe-se que o magnésio (Mg) tem o potencial de reduzir a intensidade de algumas doenças em culturas de importância econômica e, portanto, o objetivo desse trabalho foi verificar o efeito de diferentes doses desse macronutriente na resistência do arroz à mancha parda. Para isto, plantas de arroz (cv. Metica-1) foram cultivadas em solução nutritiva contendo 0,25; 0,5; 1; 2 e 4 mmol.L-1 de Mg. Foram avaliados o período de incubação (PI), o número de lesões (NL) por cm² de folha, a severidade da mancha parda e a concentração foliar de Mg. Os dados de severidade foram usados para calcular a área abaixo da curva do progresso da mancha parda (AACPMP). Outro experimento com as doses de 0,25; 2,5 e 4 mmol.L-1 de Mg foi conduzido para determinar a concentração de aldeído malônico (MDA) e a atividade da quitinase (QUI), β-1,3-glucanase (GLU), peroxidase (POX), polifenoloxidase (PFO) e fenilalanina amônia-liase (FAL) em resposta à infecção por B. oryzae. Houve efeito linear positivo e linear negativo das doses crescentes de Mg, respectivamente, na concentração foliar de Mg e na AACPMP. Houve efeito quadrático das doses crescentes de Mg no PI e no NL por cm² de área foliar. Alta concentração de MDA e maior atividade da PFO ocorreram com a dose de 4 mmol.L-1 de Mg. As atividades da QUI e da GLU não foram afetadas pelas doses de Mg. A maior atividade da POX ocorreu para as plantas supridas com as doses de 2,5 e 4 mmol.L-1 de Mg. A FAL apresentou aumento significativo em atividade às 48 e 72 horas após inoculação com a dose de 4 mmol.L-1 Mg. Os resultados desse estudo demonstram que a alta concentração foliar de Mg aumentou a resistência do arroz à infecção por B. oryzae principalmente por meio do aumento das atividades das enzimas de defesa.

Brown spot, caused by the fungus Bipolaris oryzae, is one of the most important rice diseases. It is known that magnesium (Mg) has the potential to decrease the intensity of some diseases in crops of economic importance. Therefore, the aim of this study was to determine the effect of different Mg rates on rice resistance to brown spot. Rice plants (cv. Metica-1) were grown in nutrient solution containing 0.25, 0.5, 1, 2 and 4 mmol.L-1 Mg. The incubation period (IP), the number of lesions (NL) per cm² of leaf, the brown spot severity, and the foliar concentration of Mg were evaluated. Data from severity were used to calculate the area under brown spot progress curve (AUBSPC). Another experiment with the rates of 0.25, 2.5 and 4 mmol.L-1 Mg was carried out to determined the concentration of malondialdehyde (MDA) and the activity of chitinase (CHI), β-1,3-glucanase (GLU), peroxidase (POX), polyphenoloxidase (PPO) and phenylalanine ammonia-lyase (PAL) in response to B. oryzae inoculation. There were linear positive and linear negative effects of the Mg rates on the foliar concentration of Mg and AUBSPC. There was quadratic effect of the Mg rates on both IP and NL per cm² of leaf area. The highest concentration of MDA and high PPO activity were obtained with the rate of 4 mmol.L-1 Mg. The activities of CHI and GLU were not affected by the Mg rates. High POX activity occurred for plants supplied with 2.5 and 4 mmol.L-1 Mg. Significant increase in PAL activity occurred at 48 and 72 hours after inoculation at the rate of 4 mmol.L-1 Mg. The results of this study demonstrated that the high foliar concentration of Mg increased rice resistance to infection by B. oryzae mainly through the increase on the activities of defense enzymes.