Identity and pathogenicity of Diaporthe species causing canker and dieback on twigs of Rhus chinensis in Southwest China

Chinese gallnuts are widely used in medicine and chemicals due to their high tannin acid content. Rhus chinensis, the main host of the gall aphid, produces horned gallnuts that account for more than 70 % of all Chinese gallnut production. Fungal diseases like canker and dieback on R. chinensis threaten gall quality and yield, but little is known about their causative fungi. In 2021, twig canker and dieback affected 67.7 % of R. chinensis plants in Niujie Town, Yunnan province, Southwest China. Our study revealed that Diaporthe spp. are the main agents of the diseases, based on morphology, multigene phylogeny (ITS, tef1-α, tub2, his3 and cal), and pathogenicity tests. This is the first study of identity and pathogenicity of Diaporthe species causing twig canker and dieback on R. chinensis. Diaporthe spp. were isolated from all 11 diseased samples, with six common species identified, belonging to two sections: Section Eres (D. apiculata, D. citrichinensis, D. eres, and D. oraccinii) and Section Sojae (D. orixae and D. soja). Section Eres was predominant (IR = 42.7 %), with the D. citrichinensis species complex (D. citrichinensis and D. oraccinii) as the dominant taxon. Four tested species (D. citrichinensis, D. eres, D. oraccinii, and D. orixae) caused lesions and/or dieback on 5-year-old twigs of R. chinensis in in vivo pathogenicity tests. This finding provides a foundation for disease management in gallnut production and further exploration of how fungi overcome tannin-based plant defenses and their role in plant disease, aiding in developing effective control strategies against these fungal pathogens.