Abstract
ABSTRACT The use of bacteria in growth promotion and biological control of plant diseases can minimize environmental contamination caused by the indiscriminate use of pesticides and chemical fertilizers. We aimed to evaluate growth promotion and biological control of Corynespora cassiicola in tomato seedlings mediated by beneficial bacteria isolated from a non-rhizospheric Amazon soil containing different amounts of biochar, and to identify to which groups of bacteria the strains belong. We obtained 200 strains of bacteria from experimental plots containing biochar doses of 0, 40, 80 and 120 t ha-1. Of these, 53 strains were selected by root colonization tests. Based on growth promotion parameters, 25 strains were screened, identified by molecular characterization and evaluated for indoleacetic acid (IAA) production, phosphate solubilization and biological control. The best dose of biochar for colony formation was 40 t ha-1, and a regression model indicated 34 t ha-1 as the optimal dose. The production of IAA was observed in 18 (75%) strains, and two (8%) strains were able to solubilize phosphate. The efficiency in root growth promotion was up to 125%, and the percentage of plant protection ranged from 50 to 59%. Molecular characterization showed that the bacteria used in this study belong to the genera Bacillus and Lysinibacillus.
Highlights
Tomato (Solanum lycopersicon Linnaeus) is one of the most commonly produced vegetables worldwide (Faostat 2017)
Our results suggest that biochar enhancement in higher doses reduces the population of cultivable bacteria in nonrhizospheric soil and intere negatively with the survival of bacterial groups capable of actively colonizing the rhizosphere of tomato seedlings, while having beneficial effects on bacteria of the B. megaterium group capable of solubilizing phosphate
The growth rate of Bacillus subtilis SL-13 in NB medium increased with the addition of biochar, because it contains nutrients for the growth of these bacteria and the special porous structure of the biochar has a positive effect on the adsorption of bacteria, being a potentially suitable carrier of plant growth-promoting rhizobacteria (PGPR) for agriculture (Tao et al 2018)
Summary
Tomato (Solanum lycopersicon Linnaeus) is one of the most commonly produced vegetables worldwide (Faostat 2017). Target spot, caused by the fungus Corynespora cassiicola Corynespora cassiicola is non-specific and occurs mainly in the tropics and subtropics (Dixon et al 2009), where environmental conditions favour disease development (Teramoto et al 2017). In Brazil, there are still no specific fungicides recommended by the Ministry of Agriculture for the control of target spot in tomato crops. The disease is controlled by fungicides recommended for soybean crops, such as Carbendazim Nortox® and Comet®, which have benzimidazole and strobirulin, respectively, as active ingredients (Agrofit 2020). These agents can cause harm to the environment, plants, animals and humans (Chaturvedi et al 2013)
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