Evaluation of a Novel Streptomyces avermitilis Strain from Egyptian Soil for Biological Control of Tetranychus urticae in Greenhouse Cucumber Plantations

Background: Infestation in greenhouse cucumber with the two-spotted spider mite (Tetranychus urticae Koch) commonly causes severe damage to crop quality and quantity and increases crop production costs. Objective: This study was conducted to investigate the efficacy of high-abamectinproducing isolates of S. avermitilis against T. urticae-infested cucumber and to assess their impact on biochemical stress markers in these vegetables. Methods: In this study, 72 non-antagonistic Streptomyces were isolated from rhizospheric soil samples collected from eight different locations in Egypt and screened for their ability to produce the secondary metabolite, abamectin Results: The screening process identified two potent abamectin-producing isolates, EW8 and T2, which produced 42.7 and 29.6 μg/L abamectin, respectively, as confirmed by LC-MS/MS analysis. According to DNA sequence analysis of the 16S rRNA gene, these two isolates belong to the species S. avermitilis. The acaricidal activity of either culture suspensions of S. avermitilis strains WE8 and T2, or their extracts containing abamectin, against the mobile stages and egg hatchability of T. urticae was evaluated in the laboratory and the greenhouse. Data on the mortality among the examined female mites and the reduction in their number of eggs point out a potential acaricidal activity of the examined strains of S. avermitilis and their extracts containing abamectin against T. urticaes. Furthermore, the extracts containing abamectin from these two S. avermitilis strains induced oxidative stress in the infested cucumber plants by T. urticaes, as indicated by increased levels of malondialdehyde (MDA). However, the levels of MDA in T. urticae-infested cucumber plants varied depending on the strain and the specific abamectin crude extract used. Conclusion: S. avermitilis strains T2 or WE8, or their crude extract could be applied in greenhouse cucumber plantations to combat red mite infestation (Fig. 1).