Bacillus subtilis E Bacillus licheniformis na promoção de crescimento e no controle da murcha de Fusarium no tomateiro

Abstract

Tomato plants are affected by several pests and diseases, including tomato Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici (FOL), which is considered as one of the most destructive vascular disease of tomato. Tomato Fusarium wilt can cause serious economic losses (up to 100% in production), being considered difficult to control. Although resistant cultivars provide the best method to manage tomato Fusarium wilt, the occurrence of new aggressive races of the pathogen has been a challenge for producers. Biological control may be an effective and promising alternative for management when planting varieties susceptible to the pathogen. The objectives of this study were to evaluate the effects of Bacillus subtilis and Bacillus licheniformis, alone or in mixture, to promote plant growth and in the control of tomato Fusarium wilt caused by F. oxysporum f. sp. lycopersici race 3. The ability of mixture of B. subtilis and B. licheniformis (Quartzo®) strains to promote the growth of tomato plants was evaluated in plastic pots applying 1 x 108, 1 x 109 and 1 x 1010 CFU mL- 1, as well as applying cell suspension of B. subtilis and B. licheniformis, in mixture and separately, at 1 x 108 CFU mL-1 concentration in plants developed in rizotrons (100 cm x 17.5 cm). Plant height (cm), stem base diameter (mm), root and shoot fresh and dry mass (g) and root volume (mL) and length (cm) were evaluated. To evaluate the effect of B. subtilis and B. licheniformis in the control of Fusarium wilt, tomato seedlings were transplanted into substrate infested with FOL (2 x 105 chlamydospores g-1 substrate). These studies were divided into two parts, in the first part was evaluated the application of the mixture of B. subtilis and B. licheniformis in the concentration of 1 x 1010 CFU mL-1, and in the second part, the Bacillus were applied separately in the concentration of 1 x 108 CFU mL-1. Plant height (cm), stem base diameter (mm), root and shoot fresh and dry mass (g), and the severity disease (internal and external symptoms) were evaluated. Bacillus isolates, applied in mixture or separately, promote plant growth, especially the roots. The mixture of the isolates was not effective in controlling tomato Fusarium wilt. However, the application of the strains separately, reduces the symptoms of the disease and allows greater growth of the treated plants. Also, the application of the mixture at a concentration of 1 x 108 CFU mL-1 reduces the severity of the disease. Bacillus subtilis and B. licheniformis isolates were detected both in the rhizosphere and in the sap of the treated plants. The application of B. subtilis and B. licheniformis isolates, in mixture or separately, in substrate without the pathogen, was efficient to promote plant growth of tomato plants.