role of leaf pigment and antioxidant levels in UV-B resistance of dark- and light-green Kentucky bluegrass cultivars

Ultraviolet-B [UV-B (280-320 nm)] radiation is one of the major factors causing quality decline of transplanted sod. Pigments and antioxidants are associated with plant stress resistance, but their roles in turfgrass tolerance to UV-B damage are not well understood. The objectives of this study were to determine if kentucky bluegrass (Poa pratensis L.) cultivars with darker green genetic leaf color possessed greater pigment and antioxidant defense capacities and if such characteristics were associated with greater resistance to UV-B. Two cultivars, 'Moonlight' (dark green) and 'Limerick' (light green), were selected and subjected to continuous, artificial UV-B radiation (70 micromol.m(-2).s(-1)). UV-B irradiation reduced turf quality by 58% ('Moonlight') and 77% ('Limerick') relative to day 1 when measured 10 days after initiation of UV-B exposure. Higher canopy photochemical efficiency (PEc) was found in 'Moonlight' relative to 'Limerick' under UV-B stress and during recovery. 'Moonlight' contained greater levels of chlorophyll (1.5 to 1.6-fold), carotenoids (1.3-fold), superoxide dismutase [SOD (1.0-fold)] and catalase [CAT (1.5-fold)] than 'Limerick' when measured at 10 days after UV-B initiation. Turfgrass quality and PEc were positively correlated with pigments (chlorophyll and carotenoids) and antioxidant enzymes (SOD and CAT), and negatively correlated with lipid peroxidation. The results suggest that selecting dark-green cultivars with greater pigment content and antioxidant activity may be an effective approach for turfgrass breeders and sod producers to improve tolerance of newly transplanted sod to environments with higher UV-B radiation.