Bactérias com atividade de ACC-desaminase na mitigação do déficit hídrico e de Meloidogyne javanica em tomateiro

Abstract

The modern agriculture faces increasing challenges due to biotic and abiotic factors that threaten crop sustainability and global food security. Stressful conditions such as parasitism by plant nematodes and exacerbated water stress intensify negative effects on plants that, in response, activate the synthesis of the gaseous plant hormone called ethylene. Through passive diffusion, the hormone is rapidly mobilized by plant tissues. When ethylene concentrations exceed the ideal limit for growth and development of plant tissues, it triggers harmful effects on the plant such as inhibition of germination, root elongation, destruction of chlorophyll, and senescence and defoliation of leaves. In view of the above, the objective was to perform a bioprospection and characterization of bacteria with ACC-deaminase activity with potential for bioinoculation in mitigating the damage caused by Meloidogyne javanica infestations and water restriction in tomato crops. Three experiments were carried out, each addressing specific aspects of the potential of these bacteria to promote tolerance to environmental stresses. Initially, 105 bacterial isolates from different species were tested and evaluated for the production of ACC-deaminase, an enzyme that reduces ethylene levels in plants under stress. Among the isolates, 80% demonstrated ACC-deaminase activity, with emphasis on strains of Bacillus pumilus, Bacillus thuringiensis and Lysinibacillus sphaericus, which presented high enzymatic activity. These isolates demonstrated great potential to be used as bioinoculants in promoting stress tolerance in plants. In the second experiment, the efficacy of bacteria in improving germination and development of tomato seedlings under water stress induced by polyethylene glycol 6000 was tested. Under conditions of different bacterial treatments and levels of osmotic stress, the results indicated that the isolate RZ-1 was effective in promoting germination and root and shoot growth of seedlings, especially in moderate stress situations (-0.4 MPa). The third study explored the potential of isolates with ACC-deaminase activity to mitigate the effects of water deficit and root-knot nematode infestation in tomato plants. The experiment was set up in a randomized block design, with a 2 (moisture levels) x 10 factorial scheme, with ACC-deaminase-producing bacterial isolates and a control without bacteria in soil conditions infested with M. javanica. The isolates E-45, RZ-1, E-69 and RZ-76 demonstrated significant improvement in plant biomass 16 and reduced nematode infestation. The isolate RZ-1 was particularly effective in reducing the number of galls and the population of second-stage juvenile nematodes. 80% of the tested isolates reduced the reproduction of Meloidogyne javanica, even under water stress conditions. These studies indicate that bacteria with ACC-deaminase activity represent a valuable tool for sustainable agriculture, promoting plant tolerance to water stress and infection by the phytopathogen Meloidogyne javanica, demonstrating high potential to improve tomato productivity under adverse growing conditions.