Rizobactérias como agentes biológicos no controle de Meloidogyne incognita em alface

Abstract

Lettuce cultivation (Lactuca sativa L.) faces considerable challenges due to the presence of root-knot nematodes (Meloidogyne spp.), which are highly harmful and significantly affect the crop. Understanding the mechanisms by which these nematodes are attracted to and infect host plants is essential for the development of effective control strategies. Plant growth-promoting bacteria not only enhance plant development and growth but also interfere with nematode attraction and behavior by modifying root exudates, thus establishing themselves as an effective approach in the management of root-knot nematodes. Chemotaxis plays a crucial role in this process, acting as a mechanism by which nematodes detect chemical signals and orient themselves toward plant roots. Bacteria of the genus Bacillus spp. have been widely studied due to their ability to interfere with this process, either by promoting repellence or by hindering nematode access to the roots. Thus, the objective of this study was to evaluate the potential of bacterial isolates in the control of Meloidogyne incognita and in promoting lettuce growth, focusing on chemotactic interaction and the influence of these microorganisms on nematode behavior. For this purpose, phytotechnical, biochemical, and microbiological evaluations were carried out, including nematode population density, plant growth, and root colonization by bacteria. The isolates were compared with a commercial control (BioMagno) and a negative control (plants inoculated with incognita, but without the application of bacteria). Evaluations of plant development variables and the nematode reproduction factor were performed 45 days after inoculation, allowing the effects of bacteria on both phytopathogen control and lettuce growth promotion to be understood. The experiment was conducted in two different periods in order to confirm the obtained results. The results showed that inoculation with bacteria promoted significant improvements in lettuce development and in the control of M. incognita. In the chemotaxis assay, the isolates of Bacillus thuringiensis and Pseudomonas aeruginosa showed the greatest repellent effect, reducing the attractiveness of the roots to nematode juveniles. Regarding phytotechnical parameters, plants treated with bacteria, especially the Bacillus isolates, showed greater biomass accumulation and improved nutritional status (higher N and P contents) compared with the infected control. In addition, the isolate Bacillus pumilus stood out due to the marked reduction in the number of galls and the reproduction factor, demonstrating high efficiency in biological control. It is concluded that the use of these bacteria represents a viable biotechnological alternative, acting both in the initial repellence and in the population suppression of the nematode, as well as in the promotion of plant growth.