Foliar application of <i>Verticillium dahliae</i> Aspf2‐like protein improved the heat tolerance of creeping bentgrass by regulating photosynthetic and antioxidant capabilities

Abstract Continuous high ambient temperature in hot summer months leads to a sharp decline in turf quality of cool‐season turfgrass. Verticillium dahliae Aspf2‐like protein (VDAL) is a secretory protein of V. dahliae that can improve crop yield and resistance to disease, but its role in improving heat tolerance of cool‐season turfgrass has not been reported so far. The objectives of this study were to explore the effect and mechanism of foliar application of VDAL on improving heat tolerance in cool‐season creeping bentgrass ( Agrostis stolonifera ) and to further examine the advantage of foliar spraying with VDAL in mitigating summer bentgrass decline (SBD) in the US transition zone or other regions with similar climate. The results demonstrated that the optimal dose of VDAL for improving thermotolerance of two creeping bentgrass cultivars (heat‐tolerant 13 M and heat‐sensitive Seaside II) was screened as 0.2 g L −1 based on analyses of chlorophyll content, photochemical efficiency of PSII, and cell membrane stability under controlled heat stress conditions. Foliar application of the optimal dose of VDAL significantly restricted chlorophyll loss under heat stress and also alleviated heat‐induced declines in net photosynthetic rate, transpiration rate, stomatal conductance, and water use efficiency. In addition, overaccumulations of superoxide anion radical and hydrogen peroxide could be significantly alleviated by the exogenous application of VDAL through improving the activity of antioxidant enzymes including superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase in two cultivars. A further 2‐year field trial showed that foliar application of VDAL improved turf quality, chlorophyll content, photochemical efficiency, and cell membrane stability of the two cultivars during hot summer months of 2022 and 2023. The results indicate that the appropriate dose of VDAL plays a positive role in photosynthetic performance and antioxidant capacity for thermotolerance of creeping bentgrass, and foliar application of VDAL could be considered an effective approach for alleviating SBD.