Combined application of effective Trichoderma, Pseudomonas and arbuscular mycorrhiza spp. reduced soil-borne diseases and boosted growth in cotton

Background The most common soil-borne diseases in cotton are root rot and wilt, which are caused by Rhizoctonia solani (Taub) Butler and Fusarium oxysporum f. sp. vasinfectum, respectively. These two diseases significantly reduce plant stand and production. Under extreme circumstances, the application of fungicides does not provide satisfactory management of these diseases and also pollutes the environment. The effect of biocontrol agents, their combinations and fungicides on root rot and wilt management and plant growth in Gossypium hirsutum and G. arboreum cultivars CSH-3129 and CICR-3 were studied during 2017-18 and 2018-19.Results Out of six isolates of Trichoderma spp., T. asperellum (Th-11) was the most effective for inhibiting the mycelial growth of R. solani and F. oxysporum f. sp. vasinfectum (64.4-100%). The combined seed treatment of T. asperellum (Th-11, c.f.u. 2 x 10(8)/g) + Pseudomonas fluorescens (c.f.u. 2 x 10(8)/g) + arbuscular mycorrhizal fungi (AMF; 1200 IP/g) resulted in the highest plant vigour index in CSH-3129 (890.9%) and CICR-3 cultivars (393.5%) at 15 days after treatment. Ninety days after sowing, the combined seed treatments of T. asperellum (Th-11) + P. fluorescens + AMF followed by T. asperellum (Th-11) + P. fluorescens showed the lowest area under the disease progress curve in CICR-3 and CSH 3129. Two-year pooled results indicated that the combined seed treatment with T. asperellum (Th-11) + P. fluorescens + AMF reduced the root rot disease by 51 and 57.5% in CICR-3 and CSH-3129 cultivars, respectively, under field conditions.Conclusion The present investigation suggested that combined application of the most effective strains of T. asperellum (Th-11) @10 g/kg + P. fluorescens @10 g/kg and AMF @20 g/kg can effectively manage root rot and wilt diseases up to 60 days after sowing and enhance plant growth under field conditions. However, the application rates of these biocontrol agents vis-a-vis load of pathogen inoculum in the field must be further evaluated for improved and long-term effects.