Synergism between Streptomyces viridosporus HH1 and Rhizophagus irregularis Effectively Induces Defense Responses to Fusarium Wilt of Pea and Improves Plant Growth and Yield

Fusarium wilt is a detrimental disease of pea crop, resulting in severe damage and a reduction in its yield. Developing synergistically enhanced bioagents for disease management and growth promotion is pivotal for food safety, security, and sustainability. In this study, biocontrol potential of treating pea plants with Streptomyces viridosporus HH1 and/or their colonization with Rhizophagus irregularis against infection with Fusarium wilt was investigated. Impacts on the expression profiles of defense-related genes, biochemical, and ultrastructural levels, as well as the growth and yield of pea plants in response to these treatments, were also investigated. Data obtained indicated the antifungal activity of S. viridosporus HH1 against F. oxysporum f.sp. pisi in vitro. Furthermore, the GC-MS analysis revealed production of different bioactive compounds by S. viridosporus HH1, including 2,3-butanediol, thioglycolic acid, and phthalic acid. The results from the greenhouse experiment exhibited a synergistic biocontrol activity, resulting in a 77% reduction in disease severity in pea plants treated with S. viridosporus HH1 and colonized with R. irregularis. In this regard, this dual treatment overexpressed the responsive factor JERF3 (5.6-fold) and the defense-related genes β-1,3-glucanase (8.2-fold) and the pathogenesis-related protein 1 (14.5-fold), enhanced the total phenolic content (99.5%), induced the antioxidant activity of peroxidase (64.3%) and polyphenol oxidase (31.6%) enzymes in pea plants, reduced the antioxidant stress, and improved their hypersensitivity at the ultrastructural level in response to the Fusarium wilt pathogen. Moreover, a synergistic growth-promoting effect was also recorded in pea plants in response to this dual treatment. In this regard, due to this dual treatment, elevated levels of photosynthetic pigments and improved growth parameters were observed in pea leaves, leading to an increment in the yield (113%). In addition, application of S. viridosporus enhanced the colonization levels with R. irregularis in pea roots. Based on the obtained data, we can conclude that treating pea plants with S. viridosporus HH1 and colonization with R. irregularis have synergistic biocontrol activity and growth-promoting effects on pea plants against Fusarium wilt. Despite its eco-safety and effectiveness, a field evaluation of this treatment before a use recommendation is quite necessary.