Chlorophyll fluorescence response of
and ‘Muscat Hamburg’ under two combined drought−cold stress modes. (a)−(c) indicate the response of Fo
(b) and Fv/Fo
(c) to gradient cooling (GC) mode, while (d)−(f) represent the response of Fo
(e) and Fv/Fo
(f) to non−acclimated freezing (NAF) mode. The values were the mean value±SE of three replicates, and * and ** indicate significant differences between V. amurensis and ‘Muscat Hamburg’ at P<0.05 and P<0.01 level (t test), respectively.