α-tocopherol and β-carotene concentrations in tropical grasses as affected by increasing daylength

Extended daylength substantially increases the total mass of subtropical forages. An experiment was designed with four forages to determine the result of altered plant growth as a result of extended daylength on concentrations of P-carotene and alpha-tocopherol. Pure stands of Florakirk and Tifton-85 bermudagrass (Cynodon dactylon), Florona stargrass (Cynodon nlemfuensis Vanderyst) and Pensacola bahiagrass (Paspalum notatum Fluegge) were established in central Florida during the summer of 1997. Individual grass plots were exposed to two daylength treatments, extended (artificial light used to maintain daylength at 15 h) and normal daylength, conducted over a seven-month period. Samples were harvested at distances of 4 m 'behind' the light and 1.0 m 'in front' of the light. Samples were collected and analyzed for beta-carotene and alpha-tocopherol at six sample dates from late fall to early spring. Extended daylength increased forage yields from 32 to 258% over normal daylength. However, there was no difference between forage alpha-tocopherol and beta-carotene concentrations of the grasses between normal and extended daylength. Tifton-85 had the lowest mean forage concentrations of beta-carotene (37 mug g(-1)) and alpha-tocopherol (22.6 mug g(-1)). January forages had the lowest concentrations of a-tocopherol while the lowest beta-carotene concentrations were found in February. Frost dramatically reduced both beta-carotene and alpha-tocopherol concentrations. Forage concentrations of a-tocopherol and beta-carotene were not substantially affected by increased daylength and were able to meet livestock requirements. However, concentrations of these vitamins were low from October to January.