Potential of a halophyte-associated endophytic fungus for sustaining Chinese white poplar growth under salinity

Abstract

Endophyte-mediated plant growth and stress tolerance have been increasingly acknowledged. Our knowledge of functions of endophytes from saline environments, however, is currently scant indeed. In this work, we found that an endophytic ascomycetous Curvularia sp. isolated from a halophytic plant Suaeda salsa was able to establish beneficial symbiosis with poplar (Populus tomentosa). Microscopic staining technique confirmed that the Curvularia sp. can penetrate the poplar roots after two week inoculation and readily form sclerotia-like structures and monilioid hyphal cells in root hair and/or cortex cells, both intercellularly and intracellularly. This implied that this fungus can be referred to as a dark septate endophyte. Pot experiments revealed that Curvularia sp. significantly promoted the poplar growth and resulted in increased production of the antioxidant enzymes, particularly the superoxide dismutase (SOD) and ascorbate peroxidase (APX) under salinity stress condition. The presence of Curvularia sp. also enhanced chlorophyll a, b and proline contents in leaves, although not all differences were significant. Compared to the non-inoculated plants, the photosystem II-based electron transport rate (ETR), actual quantum yield in the light-adapted steady state (ϕPSII) and photochemical quenching values (qP) was significantly higher in colonized plants, despite there were only slight differences in the values of the maximum quantum yield in the dark-adapted state (Fv/Fm) and in the light-adapted sate (F’v/F’m). Collectively, our data supports the evidence of the ability of Curvularia sp. to alleviate the adverse effects of salinity stress on poplar growth and highlights the potential use of endophytes from extreme conditions as novel probiotics in improving salt tolerance of tree seedlings.