Biocontrol of root rot complex disease of Phaseolus vulgaris by Streptomyces sp. strains in the field

Soil-borne pathogens associated with root rot complex diseases cause major yield losses in common bean (Phaseolus vulgaris L.) worldwide. The lack of active ingredients available against these pathogens makes disease control difficult. Seed treatments with Streptomyces spp. have been described as a potential ecofriendly strategy against this complex disease. Here, we evaluate the effect of Streptomyces sp. strains CBQ-EA2 and CBQ-B-8 as biological control agents (BCAs) against root rot complex disease of P. vulgaris, mainly caused by Macrophomina phaseolina and Rhizoctonia solani under natural field conditions in Cuba. To this end, seed treatments with Streptomyces sp. strains CBQ-EA2 and CBQ-B-8, using single or mixed applications, were examined. Seed treatments with the BCA Trichoderma harzianum Rifai A-34 and the chemical Celest (R) Top 312 FS were included for comparison. In all experimental fields, treatments with Streptomyces spp. had significantly higher efficacy in reducing disease incidence (DI) and disease severity (DS) than the chemical Celest (R) Top 312 FS, and a similar effect as that by the BCA T. harzianum A-34. Most of the treatments evaluated showed higher germination, quality and yield of legumes than the nontreated control. Seed treatments using the combination of the two actinobacterial strains (Streptomyces sp. CBQ-EA-2+ CBQ-B-8) showed higher effectiveness in reducing DI and DS, and enhancing germination, yield and quality of legumes compared with the nontreated control, with a similar effect as that with the BCA T. harzianum A-34 and the chemical Celest (R) Top 312 FS. Overall, microbial consortia deserve further research in the future to develop potential biological products for crop protection.

Automated summary

Soil-borne pathogens associated with root rot complex diseases have devastating effects on global common bean (Phaseolus vulgaris L.) yield. In this study, the potential of Streptomyces sp. strains CBQ-EA2 and CBQ-B-8 as biological control agents (BCAs) against root rot complex disease of P. vulgaris was evaluated under natural field conditions in Cuba. Seed treatments with these strains showed significantly higher efficacy in disease reduction than the chemical control and had similar effects as the BCA T. harzianum A-34. The combination of the two Streptomyces strains exhibited the best results in disease reduction and improved germination, yield, and quality of legumes. The findings suggest that microbial consortia should be further researched for the development of biological products for crop protection.