Biocontrol of Pythium root rot on lisianthus using a new dark septate endophytic fungus Hyaloscypha variabilis J1PC1

Pythium root rot is one of the most destructive diseases on lisianthus in Japan. Current management strategies against Pythium root rot are insufficient in controlling the disease especially on hydroponically grown lisianthus. This study aimed to explore the potential of dark septate endophytic (DSE) fungi to suppress the root rot disease caused by Pythium irregulare. Among the 10 DSE screened for their pathogenicity on lisianthus, seven DSE produced a positive effect on shoot growth and were thus selected for the first screening in an axenic dual-plate assay. Accordingly, the isolate J1PC1 displayed consistent disease suppression and was thus selected as a final candidate for evaluation in small- and large-scale hydroponic experiments as well as a pot experiment using commercial soil. Shoot disease severity and disease incidence were significantly reduced by J1PC1 treatment compared with that in the untreated control. The control efficacy of J1PC1 reached 50–70%, consequently producing highly marketable lisianthus plants. J1PC1 showed no signs of direct antagonism nor parasitism on P. irregulare, suggesting that other mechanisms might be involved. Real-time PCR using species-specific primers successfully detected J1PC1 from the root tissues even after 3 months of plant treatment. Using cultural, morphological, and internal transcribed spacer-based molecular analysis, J1PC1 was identified as Hyaloscypha variabilis. Collectively, our results strongly indicate that J1PC1 is a promising biocontrol agent for Pythium root rot.