Antifungal Bio-Efficacy Using Cyanobacterial Extracts and Rhizobia Against Root-Rot Disease of Faba Bean (Vicia faba L.) Plants

Abstract

The suppression effect of four biocontrol agents (i.e., cyanobacteria extracts: Nostoc linckia, Anabaena variabilis, Oscillatoria agardhii, and Spirulina sp.), in combination with Rhizobium leguminosarum biovar viceae (TAL–1148), against Rhizoctonia solani in faba bean plants was investigated through laboratory and pot experiments. After testing five R. solani isolates for pathogenicity, all of the identified fungi were found to be pathogenic and to have induced symptoms of root rot and pre- and post-damping-off. Comparing the results of in vitro experiments to the untreated control, algal extracts dramatically suppressed the pathogen's ability to develop mycelially. In comparison to the control (0%), O. agardhii showed the highest reduction (59.63%), followed by N. linckia (51.85%), A. variabilis (48.52%), and Spirulina sp. (40.37%). When compared to the other studied cyanobacteria and the control treatment, the combined effect of Rhizobium and cyanobacteria extracts (O. agardhii and N. linckia) produced the highest reduction in pre- and post-emergence damping-off, measuring 13.33 and 6.67%, respectively, in pot studies. Furthermore, in comparison to the control, these treatments enhanced the number and dry weight of nodules, shoot height, dry weight of shoots, N2%, and N content. Similar results were obtained using the fungicide Rizolex-T50%, which decreased the incidence and severity of the disease but had negative effects on Rhizobium and the symbiotic N2–fixing characteristics. Plants cultivated from treated faba bean seeds showed notable increases in the activity of the oxidative reductive enzymes (i.e., peroxidase and polyphenol oxidase). Thus, it could be concluded that using algal extracts in conjunction with R. leguminosarum was thought to be a practical, secure, and economical way to manage this type of soil-borne disease. More further studies are needed to emphasize this sustainable and eco-friendly approach using different phytopathogens.