Seleção de Bacillus de biofertilizantes e preparados biodinâmicos no controle de Fusarium oxysporum

Abstract

The chickpea is a legume rich in proteins, vitamins and fibers, which are widely used in human nutrition. However, Fusarium species represent a limiting factor for its production. The use of biofertilizer and biodynamic preparation can protect the root system and promote plant development. Thus, the objective of this study was to isolate, select and identify Bacillus from biofertilizer and biodynamic preparation with potential for in vitro control of Fusarium oxysporum. Bacillus isolates were obtained from commercial biodynamic preparation (PB500), and biodynamic preparation (PBG500) and liquid biofertilizer (BioL) of our own manufacture. To select Bacillus isolates against F. oxysporum CML2878, direct antagonism, culture pairing and production of volatile organic compounds (VOCs) experiments were performed. For direct antagonism, Bacillus isolates were spread on PDA culture medium and a 7 mm disc of F. oxysporum was placed in the center of the Petri dish. In paired cultures, F. oxysporum discs were placed at a distance of 2.5 cm in length from the streak inoculation made with a 3 μL suspension of Bacillus on PDA medium. In the VOC experiment, Bacillus isolates were grown in Petri dishes containing TSA medium overlaid with a Petri dish cultivated with F. oxysporum on PDA medium. The plates were sealed and incubated at 28 °C. Petri dishes with only the fungal isolate were considered as control. The experiments were performed in a completely randomized design, with 4 replicates. The diameter of fungal mycelial growth and the percentage of mycelial growth inhibition (MGI) were evaluated at 3, 6 and 9 days. Ten isolates were obtained from PB500 and PBG500, and 20 from BioL. The MGI of F. oxysporum varied with the isolates with the evaluation time. At 9th day of evaluation, the highest MGI of F. oxysporum (67 to 88%) occurred with the isolates from BioL and PB500 in the direct antagonism experiment. The isolates from BioL provided the highest MGI of F. oxysporum regardless of the experiment. In the VOC experiment, a greater number of isolates that provided MGI ranging from 50 to 74% were observed, while in the culture pairing experiment there was a lower number of isolates with MGI between 54 and 61%. Among the isolates obtained, the 14 most promising isolates were identified by Maldi-Tof as B. subtilis, B. cereus, Rhodococcus hoagii and nine genera of Bacillus spp. The selection of Bacillus isolates from biofertilizers and biodynamic preparations is a promising alternative for obtaining efficient and promising antagonists in controlling F. oxysporum, aiming to manage chickpea fusariosis.