In the Shangluo region of China, Salvia miltiorrhiza plants have been observed with black-brown necrosis on the aerial parts, while the roots retain an intact epidermis but display internal rot that can be easily crushed by hand. A pathogen was consistently isolated from the diseased roots and, based on colony morphology, was identified as a member of the genus Phytopythium . Molecular identification based on partial sequences of four gene regions—the nuclear ribosomal internal transcribed spacer (ITS), mitochondrial cytochrome c oxidase subunits I and II ( cox I and cox II), and β-tubulin —confirmed the morphological classification and revealed that the isolate represents a previously undescribed Phytopythium species, designated Phytopythium shangluoense after its geographic origin. Detached root inoculation assays demonstrated that P . shangluoense could cause complete root rot of S . miltiorrhiza within 15 days. Within the temperature range of 13–28 °C, seedling disease incidence reached 100% within three days after inoculation. Additionally, a set of genus-specific primers based on the ITS region was designed and validated, allowing sensitive and accurate discrimination of Phytopythium spp. from other known root pathogens of S . miltiorrhiza . Furthermore, dual culture assays and subsequent pot assays demonstrated that Streptomyces fungicidicus strain FYA1 exhibits significant inhibitory effects against P . shangluoense , achieving an efficacy of 80% against root rot caused by this pathogen. This study provides the first confirmed evidence of the isolation and designation of P. shangluoense and demonstrates that it is an aggressive oomycete plant pathogen capable of independently causing root rot and plant death in S . miltiorrhiza , offering critical insights for early diagnosis and integrated disease management.
Li et al. (Fri,) studied this question.