Potencial de rizobactérias no controle da podridão negra (Neoscytalidium sp. e Lasiodiplodia spp.) e seca (Fusarium sp.) na cultura da mandioca

Abstract

Cassava (Manihot esculenta Crantz) is a crop of significant socioeconomic importance in various regions of the world. Despite its hardiness, the crop is affected by the incidence of root diseases caused by pathogens such as Fusarium sp., Lasiodiplodia sp. and Neoscytalidium sp., which, once afflicted, express negative impacts on productivity. Rhizobacteria can act as biological control agents, becoming na efficient alternative for disease control as well as growth promoters in plant. Therefore, the aim of this study was to select rhizobacteria isolates originating from cassava roots with the potential for biocontrol of cassava dry and black rot, as well as to evaluate their ability to promote plant growth. Twenty-five bacteria were isolated from healthy roots of three cassava plants. The ilosates were characterized based on colony morphology and subsequently subjected to tests for their potential to inhibit the in vitro mycelial growth of the pathogens causing black rot (Lasiodiplodia sp. and Neoscytalidium sp.) and dry rot (Fusarium sp.), as well as their potential to promote plant growth. Of the isolates, 44% were characterized as Gram-positive, and 56% as Gram-negative. Regarding in vitro antagonistic activity, 8% of the isolates inhibited the mycelial growth of Fusarium sp., and for Lasiodiplodia sp. the rhizobacteria named BAC 4 and 10 showed reductions of 46% to 50% in Fusarium sp., growth, while BACs 4 and 7 reduced Lasiodiplodia sp. growth by 55.25% and 50.25%. Twelve percent of the isolates inhibited the mycelial growth of Neoscytalidium sp., with BACs 4, 7, and 10 exhibiting pathogen inhibition rates of 58%, 57%, and 57%, respectively, compared to the control treatment. The rhizobacteria that showed in vitro potential were tested in vivo using the BRS Novo Horizonte cassava variety. The treatments involved adding the bacterial solution to the substrate and immersing the cassava cuttings (manivas) in the bacterial solution for 5 minutes. Evaluations were conduted after 30 days. Concerning growth promotion, BAC 03, in the absence of pathogens and when incorporated into the cassava cuttings, showed the best results, with a 16.77% increase compared to the control. BAC 1 and BAC 2 did not exhibit a significant increase in growth, either in the absence or presence of pathogens. The isolate labeled BAC 3 demonstrated the best results when incorporated into cassava cuttings and in the absence of pathogens for all evaluated parameters, characterizing it as a plant growth promoter. The isolates proved to be effective both in controlling phytopathogens in vitro and promoting plant growth. Therefore, it is suggested that they can be successfully integrated into an ecologically sustainable integrated management program with great potential for use in cassava cultivation.