Evaluation of Streptomyces spp. for biocontrol of gummy stem blight (Didymella bryoniae) and growth promotion of Cucumis melo L.

Abstract

Gummy stem blight of Cucumis melo L. (melon) caused by Didymella bryoniae is a serious disease in the major production area of northwest China. Two Streptomyces isolates (Streptomyces pactum A12 and S. globisporus subsp. globisporus C28) previously isolated from the Qinghai-Tibet Plateau were investigated regarding their biocontrol of gummy stem blight and growth promotion of melon under controlled conditions. Streptomyces A12 and C28 indicated obvious antagonistic activity against D. bryoniae in vitro. Both A12 and C28 significantly decreased disease severity and AUDPC (area under the disease progress curve) of melon gummy stem blight in vivo (P < 0.05). Ten-fold dilution of C28 culture filtrate was more effective in controlling the disease compared with other treatments, the disease reduction effects were 41.0–64.2%. The mean fresh weights were increased by 40.4% for plants, 44.2% for roots, and 40.3% for aerial parts, when A12 was applied in both nursery soil and transplanted soil. Streptomyces C28 also increased the mean fresh weights of melon plants by 18.4–49.0% compared with the control in pot trial. Streptomyces A12 and C28 showed substantial colonization abilities in the rhizosphere and on the rhizoplane of melon plants. Results demonstrated that Streptomyces A12 and C28 were of positive effect on the biocontrol of gummy stem blight and growth promotion of Cucumis melo L.