Diversity and biological characteristics of cold-adaptable endophytic fungi isolated from Saussurea involucrata roots

Abstract:

[Background] Saussurea involucrata is a rare and endangered medicinal plant growing in the alpine region. However, little is known about the cold adaptation of endophytic fungi (EFs) isolated from S. involucrata. [Objective] To well understand the diversity and biological characteristics of EFs isolated from S. involucrata roots. [Methods] EFs were isolated by tissue block culture at 4℃ and 15℃, respectively. All the strains were preliminarily identified based on the ITS sequences. According to the ITS sequence similarity, strains were clustered into OTU for the diversity analysis. The representative strain (RS) of each OTU was selected, and the morphology of RSs was observed. The growth rates of RSs and the effects of RSs on S. involucrata seedling growth were investigated at different temperatures. [Results] A total of 142 strains of EFs were isolated, including 68 and 74 strains obtained at 4℃ and 15℃, respectively. The 142 strains were clustered into 14 OTUs, which belonged to 9 genera, 7 families, 5 orders, and 4 classes of 2 phyla. At 4℃ and 15℃, respectively, 10 and 11 OTUs were obtained and indicated different taxa (P<0.01). The community at 4℃ included 3 unique OTUs, in which Alternaria was the dominant genus. The community at 15℃ included 4 unique OTUs, in which Rhexocercosporidium was the dominant genus. Ten strains of dark septate endophytes (DSEs) were identified from 14 RSs, and 9 of them were psychrophiles or psychrotrophs. There were 6 RSs that could promote the growth of S. involucrata seedlings, 5 of which were DSEs, including 3 psychrotrophs and 2 psychrophiles. S11 and S12 promoted the growth of seedlings at both 15℃ and 20℃, while S01, S13, and S14 promoted the seedling growth only at 15℃. S13 and S14, the RSs of dominant Rhexocercosporidium, were DSEs and psychrotrophs capable of promoting plant growth. The plant growth-promoting effects of S01 and S12 at 15℃ were stronger than those at 20℃. Compared with those at 20℃, S01 and S12 increased the total root length of seedlings cultured at 15℃ by 2.17‒2.27 times (P<0.05). [Conclusion] The EFs isolated at 4℃ and 15℃ showed rich diversity. The isolation temperature affected the composition and structure of fungal communities. Lower temperatures were beneficial to the isolation of cold-adaptable DSEs.