Optimum levels of Paecilomyces variotii extracts in regulating resistance of rice seedlings to low temperature stress

Objectives Biostimulants are capable of alleviating abiotic stress, especially low temperature stress, and have been widely used in agriculture production. We extracted and testified a new type of biostimulant from the endophytic fungus in wild sea buckthorn. The proper dosage for the best effect was studied for rice seedlings against low temperature stress.

Methods The tested Paecilomyces variotii extracts (PVE) was obtained through fermentation and purification of the strain Paecilomyces variotii. Germination and hydroponic pot experiments were conducted using rice as tested materials. The rice seeds were germinated and grown in nutrient solution under low temperature stress (15℃). The treated PVE dosages in the nutrient solution were 0, 0.05, 0.10, 0.20, 0.50 and 1.00 μg/L, respectively. The seed germination rate, activities of antioxidant enzymes (SOD, POD and CAT), indices of photosynthetic and growth of rice seedlings were measured.

Results Comparing with no PVE (CK), the germination rates of rice seeds in PVE treatments were increased by 66.7%–106.7% on the 5th day, and by 28.2%–47.8% on the 6th day; the aboveground biomass increased by 7.9%–20.4% and the root weights by 12.5%–28.1% in the concentration range of 0.05–0.50 μg/L; the total root length, root surface area, root volume and average root diameter were increased by 48.0%, 36.6%, 36.2% and 35.2% under PVE concentration of 0.10 μg/L, respectively. Within the PVE concentrations of 0.05–0.50 μg/L, the photosynthetic rate of rice leaves was significantly increased from 5.1% to 34.4%, and the stomatal conductance and transpiration rate of leaves were increased as well. Under PVE concentration of 0.10 μg/L, the SOD, CAT and POD activities in leaves were increased by 46.9%, 9.6% and 18.4%, and those in roots were increased by 28.0%, 12.7% and 16.4%; the MDA contents in leaves and roots were reduced by 22.0% and 29.8%, respectively. The PVE could alleviate low temperature stress in the range of 0.05–0.50 μg/L, with the best effect in concentration of 0.10 μg/L.

Conclusions PVE could alleviate the low temperature stress of rice seedlings by increasing nutrient uptake area of roots, leaf photosynthetic capacity and reducing cellular oxidative damage at 0.10 μg/L concentration. The appropriate dosage of PVE is 0.10 μg/L.