Antifungal activity and resistance induction against Sclerotium cepivorum by plant growth-promoting fungi in onion plants

The influence of the inoculation with plant growth-promoting fungi (PGPF) isolates on growth enhancement of onion plants and progress of white rot disease in onions, caused by Sclerotium cepivorum, was evaluated. The tested PGPF isolates were Phoma sp. GS8-1, Phoma sp. GS 8-3, Trichoderma asperellum SKT-1, Fusarium equiseti GF18-3 and Penicillium simplicissmum GP17-2. Abnormal shape and lysis in the mycelia of the pathogen were reported in dual cultures of PGPF and S. cepivorum using scanning electron microscopy. The germination of sclerotia was reduced after soaking in culture filtrates of PGPF. The highest reduction was recorded in P. simplicissmum GP17-2 treatment (70.85%). The results demonstrated that the treatments with PGPF isolates significantly enhanced the plant height, root length, bulb perimeter and plant dry weight. Additionally, PGPF clearly reduced disease severity of white rot disease of onions. Among PGPF isolates, T. asperellum SKT-1 and P. simplicissmum GP17-2 showed the best effects in reducing the incidence and severity of white rot and enhancing onion growth. On the other hand, the levels of peroxidase and polyphenol oxidase were improved in the treated onion plants than in the untreated plants at 7 days after induction treatments. Similarly, early and strong expressions of defence genes, PR1 and PR2, were reported in plants treated with PGPF. Overall, this research suggested that PGPF treatments generated favourable effects on the suppression of white rot disease of onions.