APLICACIÓN DE Bacillus spp. PARA EL CONTROL BIOLÓGICO DE Fusarium oxysporum Schlechtend. f. sp. radicis-lycopersici EN TOMATE (Solanum lycopersicum L.)

Abstract

In Sinaloa, Mexico, the tomato crown and root rot (TFRR) represents one of the most destructive diseases, whose management is complicated by the small number of resistant hybrids and the ineffectiveness of other management methods. The use of microorganism as antagonists is a promising management strategy but it requires regional isolates against the pathogen Fusarium oxysporum f. sp. radicis-lycopersici (Forl). The goal of the present work was to select the isolate(s) that are more effective against TFRR from a set of nine bacteria from the genus Bacillus previously identified molecularly and analyzed in vitro and in planta (Cordero-Ramírez, 2008). In a first stage three bioassay with tomato cv. Missouri seedlings were evaluated in growth chambers set up at 12 hours light (25°C)/12 hours darkness (22°C). Five days old seedlings were inoculated with 1.5 x 106 CFU/ml. Ten days later the same seedlings were inoculated with 1 x 106 Forl microconidia/ml/seedling. The variables studied were plant height, dry weight of aerial and root part and severity of symptoms. The values of these variables were subjected to analysis of variance and Tukey statistical tests (p≤0.05). In a second stage three rhizocone bioassays were mounted with the best potential antagonists selected from the previous seedling bioassays. These isolates were 144, 145 and 537 the first tow identified as Bacillus subtilis and the last one as B. thuringiensis. Plant production was similar to the experiments made in the growth chamber with the difference that in this case the pathogen was inoculated at the time of transplantation to rhizocones. We found in the first stage bioassays that the isolate B. subtilis (144) is potentially antagonistic to TFRR, getting up to 87% of protection. In the second and third bioassays from the first stage experiments the isolates B. subtilis (145) and B. thuringiensis (537) showed potential antagonism against TFRR getting 40 and 52% protection to damage respectively. In the second stage assays (rhizocones) antagonism wasn’t detected in any of the isolates against TFRR. However, B. thuringiensis (537) showed significant development with respect to the absolute control, which significantly increased the height and plant dry weight.