Effects of DMI Fungicide Applications On Secondary Metabolites in Creeping Bentgrass (Agrostis stolonifera L.).

Terpenoids constitute the most prolific class of secondary metabolites.  Geranylgeranyl diphosphate (GGPP) is the 20-carbon compound in the isoprenoid pathway that gives rise to both the diterpene gibberellin (GA) compounds and the tetraterpene carotenoid pigments.  Applications of propiconazole and tebuconazole are commonly made to control diseases, but little is known about the effect they may have on carotenoid accumulation in Agrostis stolonifera.  Applications of DMI fungicides inhibit GA biosynthesis in plants.  By blocking the GA pathway, we hypothesize that the result may be a shift of metabolic precursors from normal GA synthesis to the carotenoid pathway.  Since carotenoids act as powerful antioxidants, an increase in the products in the carotenoid pathway may result in improved stress tolerance in plants.   Two applications of propiconazole and tebuconazole were made at seven day intervals at rates of 0, 976, and 1952 g a.i. ha^-1.  Leaf blades were harvested seven days after the last treatment applications.  Measurements of leaf blade F_v/F_m and digital image analysis of the plants were taken weekly.  Carotenoid and chlorophyll pigments were extracted from fresh frozen leaf blades and measured using HPLC procedures to determine treatment impacts on carotenoid metabolism.  Correlations were made among turf visual ratings, digital image analysis and the concentrations of leaf blade carotenoid and chlorophyll pigments.