Tratamentos biológicos e químicos no controle da podridão de Macrophomina e na promoção de crescimento em soja

Abstract

Gray rot, caused by Macrophomina phaseolina, is a disease that affects a wide range of hosts, especially soybeans. In adverse conditions, such as water deficit and high temperatures, the severity of the disease is increased. Therefore, this work aimed to evaluate the potential for controlling gray rot and promoting growth in soybean plants through the use of Trichoderma species, isolated or in mixture with chemical products, applied to the seeds. The Trichoderma species were: Trichoderma endophyticum, Trichoderma asperellum and Trichoderma harzianum, the growth regulator was the product Stimulate® in addition to the insecticide Thiamethoxam. In vitro and in vivo assays were developed, in a completely randomized experimental design, with 6 replications. In in vitro tests, compatibility tests were carried out with the products and Trichoderma species, and culture pairing. In vivo, the test using seeds inoculated with the pathogen or not, and subjected to treatments, was organized in a factorial scheme (2 x 12), evaluating germination, vigor and promotion of seedling growth. In pots, two inoculation methodologies were evaluated (in the substrate and in the seed) with the application of the aforementioned treatments. The potential for gray rot control and growth promotion were evaluated. Height and dry mass assessments were carried out at 15 days, and disease symptoms at 5, 10 and 15 days after emergence stabilization. The seeds used in both trials were subjected to the same treatments: Thiamethoxam alone and combined with T. asperellum, T. endophyticum or T. harzianum; plant growth regulator isolated and combined with T. asperellum, T. endophyticum, or T. harzianum; T. asperellum; T. endophyticum; T. harzianum and control. The data were subjected to analysis of variance and the means were compared using the Scott-Knott test. The chemicals were compatible with Trichoderma species. In pairing cultures, the three species of Trichoderma showed antagonistic potential against the pathogen. Seed germination and germination speed index were not responsive to the treatments used in the absence of M. phaseolina, however, when the pathogen was present in the seeds, the isolates T. asperellum, T. harzianum and T. endophyticum were highlighted these variables. In pots, disease severity was higher when the pathogen was inoculated into seeds and treatments with T. endophyticum demonstrated greater suppression of symptoms in plants. In the infested substrate, the variables did not differ between treatments. It is concluded that Trichoderma species act to control the disease and can be combined with chemical products, as well as the inoculation of the pathogen in the seeds is more severe than in the substrate, due to the time it takes for the pathogen to establish itself there.