Biological control of root rot and wilt diseases of cucumber using certain bioagents and biocides under greenhouse conditions

Abstract

Ten fungal isolates belonging to Rhizoctonia solani (4 isolates), Fusarium semitectum, F. solani, Macrophomina phaseolina, F. oxysporum f.sp. cucumerinum (2 isolates), and Sclerotium rolfsii were recovered from infected cucumber roots collected from various localities during the fall (2020) and spring (2021) growing seasons. Pathogenicity tests revealed that all isolates were capable of infecting cucumber plants, causing root rot and wilt diseases. Rhizoctonia solani isolate No. 3 was identified as the most destructive, resulting in the highest disease severity. Similarly, F. oxysporum f.sp. cucumerinum isolate No. 8 was the most virulent among the wilt pathogens. Significant variations were observed among the tested cucumber genotypes regarding their susceptibility to pre- and post-emergence damping-off. In vitro studies demonstrated that Trichoderma asperellum, T. harzianum, T. album, and T34 exhibited varying degrees of antagonistic activity against the pathogenic fungi. Additionally, different bacterial bioagents were evaluated under laboratory and greenhouse conditions; Pseudomonas fluorescens followed by Bacillus megaterium showed the highest efficacy in inhibiting the mycelial growth of R. solani and F. oxysporum f.sp. cucumerinum, whereas Bacillus subtilis exhibited moderate effects, and Paenibacillus polymyxa was the least effective. Furthermore, commercial biocides (Bio-Arc, Plant Guard, and Rizo-N) were evaluated during the fall (2022) and spring (2023) seasons under greenhouse conditions. Plant Guard was the most effective treatment at all tested concentrations in reducing disease severity caused by R. solani and F. oxysporum f.sp. cucumerinum. Moreover, Bio-Arc, followed by Rizo-N at the highest concentration, resulted in a significant reduction in the incidence of root rot and wilt diseases.