The identity, virulence, and antifungal effects of the Didymellacesous fungi associated with the Rapeseed Blackleg pathogen Leptosphaeria biglobosa

Authors: CHENG, JUNYU - Huazhong Agricultural University; LUO, TAO - Huazhong Agricultural University; ZHANG, JING - Huazhong Agricultural University; WU, MINGDE - Huazhong Agricultural University; YANG, LONG - Huazhong Agricultural University; Chen, Weidong; LI, GUOQING - Huazhong Agricultural University

Submitted to: The Journal of Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2023
Publication Date: 12/4/2023
Citation: Cheng, J., Luo, T., Zhang, J., Wu, M., Yang, L., Chen, W., Li, G. 2023. The identity, virulence, and antifungal effects of the Didymellacesous fungi associated with the Rapeseed Blackleg pathogen Leptosphaeria biglobosa. The Journal of Fungi. 9(12):1167. https://doi.org/10.3390/jof9121167.
DOI: https://doi.org/10.3390/jof9121167

Interpretive Summary: Oilseed rape is an important crop worldwide. The crop encounters several devastating diseases. One of these diseases is blackleg caused by Leptosphaeria biglobosa (Lb). During a large-scale survey of blackleg disease in China, we found eight fungal isolates (P1 to P8) that morphologically resemble the blackleg pathogen but did not cause disease on oilseed rape. Among these eight isolates, isolate P2 was identified as Didymella macrostoma and selected for extensive study to investigate biocontrol potential and biocontrol mechanisms. D. macrostoma P2 can grow on oilseed rape. Liquid growth culture filtrates of D. macrostoma P2 showed antifungal activity to the blacklet pathogen, Botrytis cinerea (gray mold) and Sclerotinia sclerotiorum (white mold). Two antimicrobal components, penicillither and Zaragozic acid A, were detected in cultures of isolates P2. This study suggests that fungal relatives of Lb are useful for screening biocontrol agents (BCAs) against rapeseed diseases, and D. macrostoma P2 is has potential as a biocontrol agent for oilseed rape diseases.

Technical Abstract: Eight fungal isolates (P1 to P8) were obtained from rapeseed stems (Brassica napus) infested with the blackleg pathogen Leptosphaeria biglobosa (Lb). They formed pycnidia with similar morphology to those of Lb, and thus were considered as Lb relatives (LbRs). In this study, the species identity of these LbRs were identified. Their virulence on rapeseed and efficacy in suppression of Lb infection were determined, and isolate P2 was selected to investigate biocontrol potential and biocontrol mechanisms. The results showed that the LbRs belong to two teleomorphic genera in the family Didymellaceae, Didymella for P1 to P7 and Boeremia for P8. Pathogenicity tests indicated the LbRs were weakly virulent, compared to Lb. Co-inoculation assays on rapeseed cotyledons demonstrated that P1 to P7 (especially P1 to P4) had a suppressive effect on Lb infection, whereas P8 had a marginal effect on Lb infection. Moreover, D. macrostoma P2 displayed more aggressive than Lb in endophytic colonization of healthy rapeseed cotyledons. Cultures of P2 in potato dextrose broth (PDB) and pycnidiospore mucilages exuded from P2 pycnidia showed antifungal activity to Lb. Further leaf assays revealed that antifungal metabolites (AM) of P2 from PDB cultures effectively suppressed infection by Lb, Botrytis cinerea (gray mold) and Sclerotinia sclerotiorum (white mold). Two AM components, penicillither and Zaragozic acid A, were detected in PDB cultures and pycnidiospore mucialges of P2. This study suggests that the LbRs are a repertoire for screening biocontrol agents (BCAs) against rapeseed diseases, and D. macrostoma P2 is a multi-functional BCA, an AM producer and an endophyte.