Controle biológico da queima-das-bainhas em arroz pela microbiolização de sementes com bactérias antagonistas

Abstract

RESUMOObjetivou-se avaliar o efeito de oito isolados bacterianos pré-selecionados de Pseudomonas synxatha, P. fluorescens, Bacillus subtilis, Bacillus sp. e Stenotrophomonas malthophilia no controle da queima-das-bainhas do arroz, causada por Rhizoctonia solani. Sementes da cultivar El Passo L144 foram imersas em suspensão (A 540 =0,5) de cada um dos isolados e agitadas por 30 min a 10�C. Sementes imersas somente em solução salina e em salina mais fungicida (Carboxin + Thiran) foram utilizadas como testemunhas. Foram semeadas 10 sementes por vaso, em quatro repetições, dispostas em delineamento completamente casualizado. Foram realizados três ensaios, sendo que no primeiro foi possível selecionar três isolados como promissores, com reduções na severidade da doença atingindo 50, 33,3 e 16,7 %, respectivamente. Estes isolados foram utilizados nos ensaios posteriores, instalados em casa de vegetação e conduzidos até o ponto de colheita, onde foi possível observar o efeito biocontrolador propiciado, principalmente, pelo isolado de P. fluorescens DFs223, com reduções significativas na severidade da doença chegando a 88 e 91,7% no segundo e terceiro ensaios respectivamente. Em ambos os ensaios, houve incremento tanto do número de panículas quanto do número de perfilhos e da massa seca de raízes em até 42,8, 81,2 e 113% respectivamente, nas plantas tratadas com o isolado de P. fluorescens DFs223.Palavras-chave adicionais: Rhizoctonia solani, Oryza sativa, biocontrole, rizobactérias. ABSTRACTBiological control of rice sheath blight by microbiolization of seeds with antagonist bacteria Eight pre-selected bacterial strains were evaluated for control of rice sheath blight caused by Rhizoctonia solani, Pseudomonas synxatha, P. fluorescens, Bacillus subtilis, Bacillus sp. and Stenotrophomonas malthopilia. Rice seeds cv. El Passo L144 were treated by immersion in a bacterial suspension (A 540 =0.5) of each isolate under agitation at 10�C for 30 min. Seeds immersed in saline solution and in saline plus fungicide (Carboxin + Thiran) were used as control. Ten seeds per pot were used, in four replications, in a completely randomized design. Three assays were performed, and in the first it was possible to select the three strains which reduced the severity of the disease, reaching 50, 33.3 and 16.7%, respectively. These isolates were used in the two last assays, which were maintained in greenhouse until the harvesting stage, where it was possible to observe the biocontrol effect, mainly by the strain of P. fluorescens DFs223, with significant reduction in the disease severity, reaching 88 and 91.7% in the second and third assays, respectively. There was an increase in the number of panicles, as well as in the number of tillers and dry mass of roots, reaching to 42.8, 81.2 and 113 % respectively, in plants treated with this isolate in both assays.Additional keywords: Rhizoctonia solani, Oryza sativa, biocontrol, rhizobacteria. INTRODUÇÃOA cultura do arroz irrigado (Oryza sativa L.) está sujeita ao ataque de várias doenças. Em quase...

Biological control of tomato bacterial spot by seed microbiolization

“…The variability in the efficacy of control of bacterial spot for the isolates used in this work (except for DFs1420) was previously registeded by Ludwig & Moura (2007) and it was associated with the stage of plant development, geographical areas (Byrne et al, 2005) or cultivars (Kavitha & Umesha, 2007). The stability of the control by the microorganism is usually associated with the performance of multiple mechanisms of action (Guetsky et al, 2001) and with an aggressive colonization of the tissues of the host plant (Kloepper & Beauchamp, 1992).…”

“…These authors reported 36.4% disease control using Pseudomonas syringae and 20 to 30% using P. fluorescens, respectively. Conversely, inconsistent result, such as that observed for DFs1296 (only effective in the first assay), is not uncommon and can be attributed to several factors (Ludwig & Moura, 2007).…”

Physiological potential of rice seeds treated with rhizobacteria or the insecticide thiamethoxam

“…Cohn). These strains were preselected, once they are able in controlling diseases and promoting development of rice plants; according to data already published by Moura, 2007 andLudwig et al, 2009.…”

“…In many crops, including rice, studies have been demonstrating the capacity of microorganisms, or chemical activators, of incrementing physiological potential of seeds treated with rhizobacteria (Freitas et al, 2003;Freitas and Aguilar-Vildoso, 2004;Ludwig and Moura, 2007) or with the insecticide thiamethoxam (Castro and Pereira, 2008).…”

Isolation, identification and in vitro evaluation of Bacillus spp. in control of Magnaporthe oryzae comparing evaluation methods

“…In a study confronting Bacillus and Pyricularia grisea (Cooke) Sacc., Velusamy and Gnanamanickam (2008) observed the effect of these bacteria on biocontrol for the production of antibiotics. While Knaak et al (2007) maltophilia is considered an effective treatment in controlling of sheath blight caused by R. solani not only by the ability of these to reduce the disease, but also by the possibility of efficiency by using them associated with compounds that stimulate its activity (Ludwig and Moura, 2007).…”