Potencial de bactérias na promoção de crescimento e biocontrole de fitonematoides em cana-de-açúcar

Abstract

Among the problems affecting sugarcane (Saccharum spp.) in Brazil, the plant parasitic nematodes are responsible for limiting the plant development and crop productivity. In this sense, management measures for these pathogens are necessary to reduce damage and preserve the biological balance of the soil and the environment. In this sense, the objectives of this study were: 1) to evaluate the potential of microbiolization of sugarcane seedlings with five rhizobacteria isolates (XT21- Arthrobacter pascens, XT23-Micrococcus luteus, XT38-Exiguobacterium acetylium, XT39-Micrococcus luteus e XT56-Bacillus megaterium) in the biocontrol of root-knot nematode (Meloidogyne javanica) root-lesion (Pratylenchus zeae) and spiral nematode (Helicotylenchus dihystera), plant development, stalk quality and sugarcane yield in the plant-cane and ratoon under field conditions; 2) to prospect the in vitro nematicidal activity of bacterial isolates on P. zeae; and, characterize these isolates for their ability to biocontrol and plant promoting growth; and, 3) to evaluate the development of seedlings of different sugarcane cultivars by microbiolization with isolates XT23, XT38 and XT39 under two irrigation forms. The treatment of seedlings with all isolates resulted in >70% suppression of M. javanica and 45% of P. zeae with XT39 isolate in plant-cane. In ratoon-cane, the highest levels of control of M. javanica were >40% in the roots with the isolates XT23, XT38 and XT39, and a reduction of 80% in the soil, regardless of the isolate. For P. zeae, although all isolates controlled the nematode in the soil and/or roots, the treatments with XT38 and XT56 resulted in control levels >40%; and for H. dihystera, suppression above 60% was observed, mainly in the sugarcane roots with XT23, XT38 and XT56 isolates. At 210 and 240 days after microbiolization (plan-cane) and second application (ratoon-cane) bacteria, the XT38 rhizobacteria using resulted in higher ºBrix in the stalks besides has resulted a chlorophyll levels increasing together XT23 and XT39 rizhobacteria treatments. Although some TSS increase occurred only in the ratoon-cane juice, an additional 18 thousand liters of sugarcane juice were produced with XT21 and XT23 in ratoon-cane. A significant increase of stalk mass was obtained using XT21 isolate in both harvests; and, with XT38 and XT23 in plant and ratoon-cane, respectively. About reducing sugars evaluations, lower glucose levels were observed with XT21 in plant-cane and with the other isolates in ratoon-cane. On the other hand, lower percentage values of cellulose and crude fiber in the stalks were observed in the treatment of seedlings with XT38. The XT21 and XT38 isolates produced the highest number of compounds related to biocontrol and plant growth promotion, the first being associated with the production of proteases, ammonium, hydrocyanic acid and auxin; and, the second, to proteases, hydrocyanic acid and phosphatase production. Evaluating the production of sugarcane seedlings, the microbiolization with XT23 and XT38 rizhobacteria was effective in increasing the fresh mass of shoots and roots, however, negative effects were observed and it may be related to the cultivar and the system of irrigation adopted.