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Tomato 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 Xg inoculation. 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.

The dieback and wilting caused by Erwinia psidii are emerging eucalypt diseases that have been observed since 2014 in the south and central-south regions of Brazil. Field observations have shown variability in disease severity resistance among Eucalyptus spp. clones and species. It is hypothesized that this variability is due to genetic resistance. To confirm this hypothesis, inoculations in genetically distinct eucalypt plants are necessary. However, lack of an inoculation method and disease assessment makes difficult to select resistant genotypes for use in commercial plantations or genetic breeding programmes. Three inoculation methods were tested on eight clones of Eucalyptus spp. Among them, inoculum deposition with bacteria-impregnated toothpick on the axillary buds was the simplest and most effective, capable to reproduce the disease symptoms observed under conditions of natural infection. We also developed a rating scale for disease assessment. Among eight clones tested, only Clone 1 (Eucalyptus saligna) and Clone 2 (Eucalyptus urophylla) were resistant.

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.Key words: Fusarium oxysporum f.sp. lycopersici, Solanum lycopersicum, biological control, host defense mechanisms, induced resistance, vascular pathogen.Rizobactérias induzem resistência contra a murcha-de-fusário do tomateiro pelo aumento das atividades de enzimas de defesa Resumo 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 murchade-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...

Currently, Xanthomonas axonopodis is one of the main foliar pathogens for Eucalyptus spp. in Brazil. It induces leaf blight and defoliation of seedlings in the nursery and young plants in the field. However, little is known about the favorable conditions for infection. The establishment and development of bacterial leaf blight caused by X. axonopodis in eucalyptus was studied for different leaf ages, temperatures and leaf wetness durations. Disease severity increased with leaf age, and the highest severity was observed on the fourth pair of completely expanded leaves (from the apex to the base). A higher level of bacterial colonization was also observed on the fourth pair of leaves quantified as bacterial cells/cm 2 of leaf area. Twelve hours of free water on the leaf surface, prior to inoculation, was essential to promote a severe infection. However, with the increase in the leaf wetness duration, a decrease in disease severity was observed. The optimal temperature for disease development was 26-30ºC.