ABSTRACT The aim of this study was to determine the behaviour of bacterial biocontrol agents (BBAs) selected to control disease in irrigated rice, in the presence of pesticides, and to study changes in the soil microbiota. We assessed the compatibility between these BBAs and pesticides using different doses of each compound, besides the impact of the BBAs on the quality and diversity of the soil microbiota under field conditions. For the microbial evaluations, rice seeds were treated with the same BBAs, in addition to the following combinations: DFs-C6 (DFs185 (Pseudomonas synxantha)/DFs306 (/unidentified)); DFs-C7 (DFs306/DFs416 (Bacillus sp.)) and DFs-C8 (DFs185/DFs306/DFs416). Saline solution was used for the control treatment. Soil samples were collected close to the roots to evaluate basal respiration, organic matter, carbon, and microbial biomass. EcoPlateTM microplates were used to determine the activity and diversity of the microbial metabolic profile. All the BBAs (DFs185, DFs223 (P. fluorescens), DFs306 and DFs416) were tolerant to the fungicides and herbicides regardless of the dose, whereas tolerance to the insecticides occurred only in the DFs416 isolate. Resistance, however, was only seen in the DFs185 (pyraclostrobin + epoxiconazole) and DFs223 (azoxystrobin) isolates. There were significant changes to the soil microbiota, especially with the DFsC06 treatment, which was the only treatment to increase the microbial biomass and quotient. Little or no difference was found in microbial metabolic activity or diversity. These results suggest the potential use of these bacterial treatments in integrated pest management, as they are resistant/tolerant to many pesticides used in rice cultivation, and some of them had a positive impact on the soil microbiota.

Resumo: O objetivo deste trabalho foi avaliar o efeito da pulverização foliar de agentes bacterianos de biocontrole (ABB) no controle do crestamento bacteriano comum do feijoeiro (CBC) e na indução de resistência sistêmica em plantas de feijão. O controle do CBC por ABB foi avaliado por meio da pulverização, em folhas de feijoeiro, 48 e 24 horas antes e depois da inoculação do patógeno (AIP e DIP, respectivamente), de: DFs93, Bacillus cereus; DFs513, Pseudomonas veronii; DFs769, B. cereus; combinação C01, DFs93 + DFs769 + DFs831 (Pseudomonas fluorescens); combinação C03, DFs348 (Bacillus sp.) + DFs769 + DFs831; e água destilada (testemunha). Os efeitos sistêmicos foram analisados após pulverização de DFs513, DFs769, C03 e água 48 e 72 horas AIP. Também foi avaliada a produção de faseolina induzida por DFs348, DFs513, DFs769, DFs831 e água. DFs513, DFs769 e C03 reduziram significativamente a incidência da doença (área abaixo da curva de progresso da doença), independentemente do momento da aplicação e da severidade da doença quando pulverizados 48 e 72 horas AIP. Os isolados DFs769 e DFs831 induziram o acúmulo de fitoalexina (faseolina). Portanto, DFs513, DFs769 e C03 apresentam potencial para o biocontrole do CBC quando pulverizados preventivamente em folhas de feijão, além de atuarem como indutores de resistência.

Abstract: The objective of this work was to evaluate the effect of foliar spraying with bacterial biocontrol agents (BBAs) on the control of common bacterial blight (CBB) of bean, and on the induction of systemic resistance in bean plants. CBB control by BBAs was evaluated by spraying bean leaves 48 and 24 hours before and after pathogen inoculation (BPI and API, respectively), with: DFs93, Bacillus cereus; DFs513, Pseudomonas veronii; DFs769, B. cereus; the C01 combination, DFs93 + DFs769 + DFs831 (Pseudomonas fluorescens); the C03 combination, DFs348 (Bacillus sp.) + DFs769 + DFs831; and water (control). Systemic effects were analyzed after spraying DFs513, DFs769, C03, and water 72 and 48 hours BPI. Phaseolin production induced by DFs348, DFs513, DFs769, DFs831, and water was also assessed. DFs513, DFs769, and C03 significantly reduced disease incidence (area under disease progress curve), regardless of spraying time and disease severity when sprayed 72 and 48 hours BPI. The DFs769 and DFs831 isolates induced the accumulation of phytoalexin (phaseolin). Therefore, DFs513, DFs769, and C03 show potential for the biocontrol of CBB when applied preventively on bean leaves, besides inducing systemic resistance.

Bipolaris oryzae e Gerlachia oryzae causadores, respectivamente, da mancha parda e da escaldadura do arroz são principalmente disseminados por sementes. Objetivou-se com esse trabalho avaliar o potencial da microbiolização de sementes para a redução da transmissão destes patógenos das sementes para as plântulas usando as bactérias DFs185 (Pseudomonas synxantha), DFs223 (P. fluorescens), DFs306 (não identificado) e DFs418 (Bacillus sp.). Duas amostras de sementes portadoras de B. oryzae e G. oryzae foram imersas em suspensão dessas bactérias, sendo a testemunha imersa em solução salina (A540 = 0,5). Após agitação (30 min./10 ºC), 400 sementes foram submetidas ao teste de sanidade pelo método do papel de filtro e o resultado indicou que o isolado DFs223 destacou-se na redução de B. oryzae e de G. oryzae nos dois lotes de sementes avaliados. Sementes tratadas conforme descrito foram dispostas em vermiculita autoclavada e a transmissão dos patógenos e promoção de crescimento avaliados após 21 dias de incubação em mesmas condições. Os isolados DFs185 e DFs306 reduziram a transmissão de ambos os patógenos, porém o isolado DFs306 foi o que proporcionou maiores incrementos de crescimento. Avaliação de antibiose in vitro mostrou que os isolados inibiram o crescimento micelial de ambos os patógenos, exceto DFs306. Pode se afirmar que estas bactérias apresentam potencial para tratar sementes visando ao controle de doenças transmitidas por estas.

Bipolaris oryzae and Gerlachia oryzae, which cause rice brown spot and leaf scald, respectively, are mainly disseminated by seeds. The aim of this study was to evaluate the potential of seeds microbiolization to reduce transmission of these pathogens to seedlings by using the bacteria DFs185 (Pseudomonas synxantha), DFs223 (P. fluorescens), DFs306 (unidentified) and DFs418 (Bacillus sp.). Seeds naturally infested/infected with both pathogens were immersed in suspension of these bacteria (A540 = 0.5) individually or in saline solution (control treatment). After 30 minutes of agitation at 10 ºC, 400 seeds were submitted to a sanity test through the blotter method and the isolate DFs223 was the best to reduce the incidence of B. oryzae and G. oryzae in both seed lots evaluated. Seeds treated like above were sowed in sterilized vermiculite. Seed transmission and growth promotion were recorded after 21 days of incubation in the same conditions. The isolates DFs185 and DFs306 reduced transmission of both pathogens, although the isolate DFs306 was the one wich gave the greatest growth increases. The evaluation of the in vitro antibiosis showed that isolates inhibited the mycelial growth of both pathogens, except DFs306. It is possible to affirm that these bacteria have the potential to be used as a seed treatment for seed-borne disease control.

Avaliou-se o efeito dos tratamentos químicos e biológicos sobre a emergência, vigor de plântulas de mamona, produção de matéria seca, além do controle de microrganismos associados às sementes das cultivares AL Guarany 2002 e Lyra. Os produtos testados foram carbendazim+thiram, carboxin+thiram e um à base de Trichoderma. A emergência total e de plântulas foram avaliadas aos 27 dias após a semeadura e a produção de matéria seca, com plantas retiradas 45 dias após a semeadura. A cv. AL Guarany 2002 apresentou maior incidência de microrganismos em relação à cv. Lyra. O tratamento químico foi 100% eficiente no controle de fungos e o tratamento biológico não reduziu a incidência de microrganismos nas sementes. O tratamento químico resultou em plantas com maior matéria seca e os melhores resultados foram para carbendazim + thiram e carboxin+ thiram, nas doses de 60 g + 140 g e 50 g + 50 g/100 kg de sementes, respectivamente. O carbendazim + thiram foi o único tratamento que se mostrou estatisticamente superior, quanto ao índice de emergência total, enquanto que o tratamento biológico aumentou os valores de emergência somente na cv. Lyra, evidenciando sua inferioridade. Destacou-se a importância dos fungicidas para o controle de patógenos associados às sementes.

The effect of chemical and biological treatments on castor bean emergence, seedling vigor, dry matter production, and also the control of microorganisms associated with seeds of the AL Guarany 2002 and Lyra cultivars, was evaluated. The products tested were carbendazim + thiram, carboxin + thiram and a product based on Trichoderma. Total seed and seedling emergence were evaluated at 27 days after sowing whereas dry matter production was verified for plants removed 45 days after sowing. The Guarany 2002 AL cultivar had a higher incidence of microorganisms than the Lyra cultivar. The chemical treatment was 100% effective in controlling fungi but the biological treatment did not reduce microorganism incidence on the seeds. Chemical treatment resulted in plants with more dry matter and the best results were for carbendazim + thiram and carboxin + thiram at doses of 60 g + 140 g and 50 g + 50 g/100 kg of seeds, respectively. The carbendazim + thiram mixture was the only treatment which was statistically higher for total emergence whereas the biological treatment increased emergence only for the Lyra cultivar, thus demonstrating its lower efficiency. The importance of fungicides to control pathogens associated with seeds was discussed.

Amplified fragment length polymorphism (AFLP) was used to analyze the genetic diversity of 14 strains of Xanthomonas arboricola pv. pruni and seven strains of X. axonopodis pv. phaseoli, which are used in xanthan production studies. Relationships identified by the AFLP profiles were assessed for xanthan production capacity, geographical location and host plant. Strains were isolated from 10 different geographic regions in South and Southeast States in Brazil. Data were analyzed for genetic similarity using the Dice coefficient and subjected to UPGMA cluster analysis. A total of 128 AFLP fragments were generated from four primer combinations: EcoRI+C/MseI+0, EcoRI+A/MseI+0, EcoRI+G/MseI+T and EcoRI+G/MseI+A. Of these, 96.1% were polymorphic. X. axonopodis pv. phaseoli (S D = 0.27) was shown to be more polymorphic than X. arboricola pv. pruni (S D = 0.58). All 14 pathovar pruni strains were included in a single main group (S D = 0.58), while the pathovar phaseoli strains were divided into three separate groups, with one group containing five strains (S D = 0.38) and two isolated groups (S D = 0.31 and 0.27) composed of only one strain each. Species were distinguished by three and eight specific AFLP markers present in the pathovar phaseoli and the pathovar pruni, respectively. For the unique strain without xanthan production capacity (X. axonopodis pv. phaseoli str. 48), nine specific AFLP bands were found. There was no evidence that geographic area or host plant influenced genetic heterogeneity. Correlations between AFLP patterns and xanthan production capacity were found in some strains, but were not consistent enough to establish a relationship.