Polysaccharide Elicitor from the Endophyte <i>Bionectria</i> sp. Fat6 Improves Growth of Tartary Buckwheat under Drought Stress

Drought can limit the growth and reduce the yield of crops, but the safe and effective bio-approach to improve the drought resistance of crops is very little. We conducted an experiment in which we monitored the effects of polysaccharide from the endophyte Bionectria sp. Fat6 on the growth of Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn) seedlings under control and drought-stressed conditions by determining gas exchange, photosynthesis parameters, photosynthetic pigment contents, and metabolite accumulation. Results indicated that the polysaccharide from endophyte stimulated plant growth and increased the aboveground biomass, root mass, and root/shoot ratio of Tartary buckwheat. Application of the polysaccharide to drought-stressed plants resulted in a significant increase in the net photosynthetic rate, stomatal conductance, and transpiration rate of Tartary buckwheat and decreased the intercellular CO₂ concentration. The contents of chlorophyll a, chlorophyll b, chlorophyll a + b, and carotenoids in leaves were higher in polysaccharide-treated seedlings than that in control. Polysaccharide notably increased the soluble protein and proline content and decreased the malondialdehyde content in Tartary buckwheat leaves. The endophytic polysaccharide may protect Tartary buckwheat against drought by improving leaf gas exchange and photosynthetic capacity, and altering concentrations of protective metabolites. Together, these changes may compensate for the negative impacts of drought stress on the growth of Tartary buckwheat. Thus, the polysaccharide from the endophyte Bionectria sp. Fat6 may be an effective biotic elicitor and a promising bio-approach to improve Tartary buckwheat production worldwide.