Seleção de bactérias como potenciais biocontroladoras do nematoide anelado do pessegueiro (Mesocriconema xenoplax)

Abstract

The peach tree short life syndrome (PTSL) associated to the ring nematode Mesocriconema xenoplax is one of the most important problems affecting peach (Prunus persica) orchards in the Rio Grande do Sul State. Currently there are not rootstocks resistant or tolerant to nematodes or register nematicides for the peach crops in Brazil, showing the need for alternative management practices. Purpose of this study was to isolate and evaluate the potential biocontrol of bacterial isolates and to select promising controllers of the ring nematodes on peach. For this, 1,219 bacterial isolates were evaluated for the production of compounds related to biocontrol and/or promotion of growth (PCRBPG) through the production of lipases, proteases, chitinases, amylases, phosphate solubilization, production of ammonia and antibiosis against Monilinia fructicola. From these analyzes were selected and analyzed 99 bacterial isolates in vitro of the M. xenoplax mortality, among these 36 isolates were selected, which showed mortality rates above 95% and evaluated for inhibition of juveniles hatching. Following, 15 isolates were selected for evaluation in vitro the root colonization of the rootstock 'GxN-9' seedlings and in vivo effect on the M. xenoplax population under cultivation peach rootstock 'GxN-9', as well as under cultivation Dianthus barbatus. Among the 1219 bacterial isolates, 92% were able to produce one or more of the eight compounds evaluated and only 1% of the isolates produced all compounds. The proteolytic activity was more frequent among bacterial isolates and hydrolysis of chitin less frequent. In the analysis of PCRBPG by habitat, 1.6% of the isolates from Soil group produced 100% of the compounds analyzed. Tagetes group concentrated 96.1% of the isolates gelatin proteolytic, 58.8% of the ammonia produced, solubilizing phosphate at 56.9% and 54.9% amylolytic; following a 9 the Liliaceae group with 70.3% of isolates Litmus® proteolytic, 63% of antibiosis against M. fructicola. Besides that, 80,6% of Gramineae isolates group produced lipases. The highest rates of production of chitinase were observed in Leguminoseae and Other. For ecological niche, the rhizosphere stands out compared with the phyllosphere and ground, as best source of potential biocontrol bacterial strains. In the mortality assay in vitro of the M xenoplax, among the 99 bacterial isolates, 84 were significant in relation to the control and 33 isolates reduced the nematode hatching compared with control. The in vitro peach root colonization was observed on 10 of the 15 isolates. Evaluation the antagonistic effect of bacteria isolates on the ring nematode on peach trees, nine bacteria reduced the nematode reproduction significantly and a significant increase for root fresh weight with isolated DFs2049 and DFs0886. The bioassay of application bacterial isolates in pre-planting to D. barbatus, there was significant reduction in the population of M. xenoplax in all treatments compared to control. Therefore, the present study that bacteria from different ecological niches show a good potential for biocontrolling M. xenoplax, nematode associated with PTSL.