Research Update

Evaluating Seaweed Extract-based Biostimulant for Improving Heat and Drought Stress Tolerance in Creeping Bentgrass

Authors: Xunzhong Zhang, Ph.D.1, Zachary Taylor, Ph.D.2, Mike Goatley, Ph.D.1, Isabel Brown1, and Kelly Kosiarski1 1School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA; 2Helena Agri-Enterprises LLC, Greenville, NC

Creeping bentgrass (Agrostis stoloniferia) experiences quality decline during summer stress. Various bioproducts have been used to improve creeping bentgrass performance during summer in the United States transition zone. Various plant biostimulants, such as extracts of brown seaweed (Ascophyllum nodosum), humic and fulvic acids, protein hydrolysates and other N-containing compounds, beneficial microorganisms, and small organic molecules, have been used for turfgrass management. Although various hormones and other hormone-like compounds have been identified in SWE, the hormonal effects of extracts of the brown seaweed Ascophyllum nodosum are explained to a large extent by the down- and upregulation of hormone biosynthetic genes in plant tissues, and to a lesser extent to the hormonal content of SWE themselves. The SWEs may protect chlorophyll, and photosynthetic function, and delay leaf senescence and also promote root growth and viability. Cytokinins can improve NaR activity and N assimilation Utilize®, a SWE –based biostimulant, is derived from extracts of brown seaweed Ascophyllum nodosum and it formulated exclusively for Helena Agri-Enterprises by Goemar (Saint Malo Cedex, France). The objectives of this study were to determine the optimum rate of foliar application of SWE-based biostimulant Utilize® for improving creeping bentgrass tolerance to heat and drought stress and quality. The experiment was conducted in the growth chamber at Virginia Tech, Blacksburg, VA. Mature ‘Penn A4’ creeping bentgrass plugs (10 cm diameter) were transplanted into plastic pots (16 cm diameter) filled with The United States Golf Associationspecified sand with 10% peat. Plants were cultured in growth chambers (Conviron, model PGC20) with temperatures at 22 /18 ºC (day/night), 70% relative humidity, 12-h photoperiod and photosynthetically active radiation (PAR) at 400 µmol·m-2·s-1. Plants were fertilized at 0.15 lb N/1000 ft2 (28-8-18 plus micronutrients) every two weeks, trimmed to 5 cm weekly, and irrigated by hand until water drained from bottom of the pots, three times per week. Plants were grown in growth chambers for about six weeks. The treatments were applied to the grass as follows: 1). Control; 2). Utilize® at 29 µL m-2; 3). Utilize® at 58 µL m-2; 4). Utilize® at 87 µL m-2; and 5). Utilize® at 116 µL m-2. There were 5 treatments with 4 replications. Fourteen days after initial application, turfgrass was subjected to heat and drought stress treatment with temperatures at 35/25 ºC (day/night). The grasses were irrigated daily to compensate for 40 – 50% of gravimetrically measured evapotranspiration (ET) loss. Physiological and metabolic data were collected biweekly and root biomass and viability were determined at the end of the trial.

The results indicated that foliar application of Utilize® at 58, 87, and 116 µL m-2 biweekly consistently improved turf quality and leaf color ratings (Fig. 1), increased leaf chlorophyll and carotenoid content, net photosynthetic rate, nitrate reductase (NaR) activity, and root growth and viability. Utilize® at 58, 87, and 116 µL m-2 increased NaR activity by 26.5%, 16.3%, and 16.3%, respectively, when compared to the control. Utilize® at 58, 87, and 116 µL m-2 increased root biomass, root length, surface area (SA), and root volume when compared to the control. The results of this study suggest that SWE-based biostimulant Utilize® improves N metabolism and root viability. Foliar application of Utilize® at 58 µL m-2 biweekly could effectively improve creeping bentgrass performance during summer stress.

Fig. 1. Leaf color response of creeping bentgrass to Seaweed extract-based biostimulant Utilize® under heat and drought stress conditions for 42 days. Left to Right: (Control), (SWE 29 µL m-2), (SWE 58 µL m-2), (SWE 87 µL m-2) and (SWE 116 µL m-2)