Methods of Assessing Bermudagrass [Cynodon dactylon] Responses to HPPD-Inhibiting Herbicides
2011
Elmore, M. T. | Brosnan, J. T. | Kopsell, D. A. | Breeden, G. K.
Mesotrione, topramezone, and tembotrione inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD), an enzyme integral to carotenoid biosynthesis. Research was conducted to evaluate the efficacy of visual bleaching and chlorophyll fluorescence yield (Fᵥ/Fₘ) measurements for estimating common bermudagrass [Cynodon dactylon (L.) Pers.] carotenoid and chlorophyll concentrations following mesotrione (0.28, 0.35, and 0.42 kg ha⁻¹), topramezone (0.018, 0.025, and 0.038 kg ha⁻¹), and tembotrione (0.092, 0.184, and 0.276 kg ha⁻¹) applications. Measurements of VB and Fᵥ/Fₘ were evaluated 3, 7, 14, 21, 28, and 35 d after application. Leaf tissues were sampled on the same dates and assayed for chlorophyll and carotenoid compounds by using high-pressure liquid chromatography methodology. Carotenoid and total chlorophyll concentrations were regressed upon VB and Fᵥ/Fₘ on each evaluation date. While significant (P < 0.05) relationships were detected on each date, variation explained by linear regression was modest (R² < 0.65); thus, neither VB nor Fᵥ/Fₘ assessments are good predictors of carotenoid and chlorophyll concentrations after HPPD-inhibiting herbicide treatment. Comparisons of R² values for VB and Fᵥ/Fₘ data suggest no advantage in using Fᵥ/Fₘ in place of VB measurements when evaluating HPPD-inhibiting herbicide activity.
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