Uso de fungos e bactérias como agentes de biocontrole no manejo das podridões radiculares na mandiocultura: isolamento, caracterização e validação do potencial antagônico

Abstract

The cassava crop, in addition to its importance in food security, also has a range of industrial uses that give it enormous potential to stimulate development and increase production yields. However, one of the most limiting biotic stresses for this crop is root rot, a complex of diseases caused by fungi that cause a high economic impact. Thus, given the scarcity of resistant varieties, damage and the low efficiency of chemical control, it is necessary to search for alternative ways to manage these diseases. In this sense, the objective of this work was to isolate and characterize microorganisms as agents of biological control of the rhizosphere and rhizoplane of cassava (Manihot esculenta) culture, testing the in vitro antagonistic potential of the isolates against phytopathogens that cause rot in the culture itself. The experiments were carried out at the Phytopathology Laboratory of Embrapa Cassava and Fruticulture. Soils and cassava roots were collected in 6 locations in the city of Cruz das Almas Bahia, where the cassava plantation was maintained consecutively for a long time, in order to isolate microorganisms from specific groups, such as Trichoderma, endospore-producing bacteria and actinobacteria, with biocontrol potential. For this purpose, selective media and the serial dilution process were used. Followed by morphological characterization and human (37 °C) and plant pathogenicity tests, with detached cassava leaf (BRS Formosa) and finally, in vitro pairings of the “double” and “four points” type to validate the antagonistic potential of the isolates obtained against phytopathogens that cause root rot. Statistical analysis of variance (ANOVA) and Scott-Knott test at 5% probability were performed using the statistical software R 4.0.4 (R CORE DEVELOPMENT TEAM, 2020). A significant amount of 117 isolates was obtained, with 1.71% belonging to the Trichoderma spp. group, 53.85% to the actinobacteria group and 44.44% belonging to the Bacillus spp. group. 98.3% of the isolates grew at 37 °C. Of the total, 11 isolates were tested for possible pathogenicity in plants and antagonistic potential in vitro, where none of them showed pathogenic characters in detached leaves and 5 of them showed significant inhibition potentials for the tested disease groups, namely: Trichoderma (TRI- FC30 and TRI-FT41), with averages above 50% inhibition, Actinobacteria (ACT-FP52, ACT-FE70) with averages of 61.12% and 50% inhibition and Bacillus BAC-FC99 with 37.5% inhibition for dry rot and 11.1% for black rot. The preliminary results of this work indicate that Trichoderma, Bacillus and actinobacteria have antagonistic/inhibitory potential against pathogens that cause cassava root rot. The cassava microbiome has the potential to obtain microorganisms with biotechnological value in the field of biological disease control.