Metabólicos rizobacterianos no controle de Sclerotinia sclerotiorum in vitro

Abstract

Sclerotinia sclerotiorum, which causes the disease known as white mold, is considered one of the most important fungal pathogens in the world and is distributed in all producing regions. Biological control is currently considered an attractive alternative to the use of agrochemicals. In this context, rhizobacteria can act as agents of biological control of diseases, since they induce systemic resistance in plants, produce antibiotics, volatile substances, metabolites, among others. The objective of this work was to evaluate the effect of volatile substances and metabolites produced by rhizobacteria on the mycelial growth of Sclerotinia sclerotiorum. The experiment was carried at the Laboratory of Phytopathology and Soil Microbiology of the Federal University of Pampa - Itaqui Campus. The experimental design was the completely randomized with 11 treatments (ten rhizobacteria plus the control) and four replicates. The volatiles test was performed with inverted and overlapping plates. Initially the rhizobacterial isolates were picked up into the liquid MB1 culture medium and kept under stirring for 24 hours at 120 rpm and 25 ° C. After 24 h, 0.1 mL of antagonist culture was added to the surface of a Petri dish containing the MB1 medium, solid, spreading with Drigalsky's loop. In another Petri dish a 5 mm diameter disc of S. sclerotiorum mycelium was transferred to the center containing the BDA culture medium. Then the cover of both plates was discarded and the bottom of one of them was used as cover for another one. Plates were sealed and incubated in a BOD chamber at 25 ° C. The control was only the S. sclerotiorum plate with the MB1 medium plate without the presence of bacteria.The evaluation of the mycelial growth of the fungus was carried out in intervals of 24 hours, measuring the colony diameter. Measurements were made until the mycelium of the control reached the border of the Petri dish. The calculation of the Mycelial Growth Rate Index (IVCM) was determined by the current diameter of the colony subtracted the diameter of the colony from the previous day divided by the day of numbers after the repication. For the metabolite test the rhizobacteria were picked in 100 mL of MB1 liquid culture medium. These were placed on a shaker table at 120 rpm for 48 hours. After this time, the vials were autoclaved for 40 minutes at 120 ° C. After this process 10% of this liquid medium was added in the BDA medium. The medium was then poured into Petri dishes and a 5 mm diameter mycelium disk of S. sclerotiorum was placed in the center. The evaluations were performed in the same way as the previous test. The data were submitted to analysis of variance and the means of each treatment were grouped by the Scott-Knott test at 5% probability. All the rhizobacterial isolates tested produce volatiles and watersoluble metabolites that inhibit the mycelial growth of Sclerotiniasclerotiorum. Isolates rhizobacterial I1and M6 are shown to be more promising for future work using rhizobacteria.