Plant growth-promoting fungi (PGPF) have attracted considerable interest as bio-fertilisers due to their multiple beneficial effects on plant quantity and quality and their positive relationship with the ecological environment. Advancements in the development of PGPF for crops and economic plant cultivation applications have been achieved, but such improvements for the use of PGPF with popular medicinal herbs, such as Salvia miltiorrhiza, are rare. In this study, we collected S. miltiorrhiza specimens inhabiting wild, semi-wild, farmland and pot-cultured areas in the Henan province of China and isolated endophytes from the roots, shoots and leaves of these samples. Twenty-eight strains of the dominant genus Alternaria were identified and selected as candidate PGPF. Under greenhouse conditions, Alternaria sp. A13 simultaneously enhanced the dry root biomass and secondary metabolite accumulation of S. miltiorrhiza as the optimal PGPF of the 28 candidate isolates. To further assess the interaction between S. miltiorrhiza and Alternaria sp. A13, the effects on seedlings growth, active ingredient accumulation, and the activity of key enzymes for effective biosynthetic pathways were investigated over a period of six months under field conditions. Compared to uninoculated seedlings, S. miltiorrhiza seedlings colonised by Alternaria sp. A13 showed significant increment of 140% in fresh weight, 138% in dry weight, and enhancement in the contents of total phenolic acid, lithospermic acids A and B (LAA and LAB, respectively) of 210%, 128% and 213%, respectively. Examination of the related enzyme activities showed that the elicitation effect of A13 on LAB accumulation correlated with cinnamic acid 4-hydroxylase (C4H) activity in the phenylpropanoid pathway under field conditions. Our results confirmed that Alternaria sp. A13 not only contributes to the stimulation of S. miltiorrhiza root growth, but also boosts the secondary metabolism, thus demonstrating its application potential as a bio-fertiliser for S. miltiorrhiza cultivation, especially in areas outside of its native growth regions.

Polyporus umbellatus is a medicinal fungus primarily used for diuresis, with its sclerotium serving as the medicinal component. The growth and development of sclerotia are reliant on a symbiotic relationship with Armillaria. However, the impact of different Armillaria species on the yield and quality of sclerotia remains unclear. In this study, three Armillaria strains, A35, A541, and A19, were identified through TEF-1α sequence analysis and phylogenetic classification. These strains were classified into three distinct species: A35 as A. ostoyae, A541 as A. gallica, while the taxonomic status of A19 remains unresolved. After four years of co-cultivation with these Armillaria strains, three groups of P. umbellatus sclerotia were harvested and labeled as A35-P, A541-P, and A19-P, respectively. The yields of A35-P, A541-P, and A19-P exhibited significant variations, with A541-P achieving the highest yield (1221 ± 258 g·nest⁻¹), followed by A35-P (979 ± 201 g·nest⁻¹), and A19-P yielding the least (591 ± 54 g·nest⁻¹). HPLC revealed significant differences in the levels of polyporusterone A and polyporusterone B among the groups. The total polysaccharide content, determined via the phenol-sulfuric acid method, also varied significantly, with A541-P recording the highest content (0.897 ± 0.042%), followed by A19-P (0.686 ± 0.058%), and A35-P showing the lowest value (0.511 ± 0.083%). PCA based on these data indicated clear distinctions among A35-P, A541-P, and A19-P, with the three groups forming separate clusters. This study, for the first time, demonstrates the effects of three different Armillaria species on the yield and active compound content of P. umbellatus. These findings provide valuable insights for selecting high-quality Armillaria strains and offer guidance for the artificial cultivation of P. umbellatus.