Applying chlorophyll fluorescence technique to cold hardiness studies of grapevines

Woody tissue cold hardiness and chlorophyll fluorescence of Concord (Vitis labruscana Bailey) grapevines were measured regularly during the dormant seasons in 1997 to 998, 1998 to 1999, and late winter 2000. Chlorophyll fluorescence was measured after a controlled freeze-stress. Fv/Fm was used as an indicator of viability. Response magnitude varied with each portion of the dormant season and the type of woody tissues. Fv/Fm temperature inflection points (temperature at which no and 100% tissue injury occurred) were closely related with T(50) (temperature at which 50% of the sample was injured) calculated from a regrowth test. Injury thresholds Fv/Fm(0), Fv/Fm(50), and Fv/Fm(100) (the Fv/Fm values when no, 50%, and 100% of the tissue were injured, respectively) are proposed for different woody tissues at three periods of the dormant season. Preliminary application of two fluorometers and field measurement was also demonstrated.