Phenological Changes in the Chlorophyll Content and Its Fluorescence in Field-Grown Sugarcane Clones Under Over-Wintering Conditions

Abstract

As a step toward breeding cultivars with tolerance to chilling stress, phenological changes in chlorophyll content (SPAD index) and its fluorescence (Fv/Fm) were investigated under over-wintering conditions using different sugarcane clones. A leading commercial cultivar in Japan, NiF8, and two interspecific lines, KY11-6114 and KY08-1200, were tested in this study. Daily minimum temperature decreased gradually with the advance of winter, and the lowest temperature of 1.2 °C was recorded in January. Although the temperature increased toward spring season, it remained below 10 °C until the end of experiment. Stem elongations in KY11-6114 and KY08-1200 during winter were significantly greater than in NiF8. The decrease in SPAD index was calculated from the difference between the beginning of winter and each measuring time. KY08-1200 and KY11-6114, with longer stem elongation, had a smaller decrease in SPAD index than NiF8 under over-wintering conditions. The Fv/Fm of all three clones decreased in January when the lowest temperature was recorded and recovered toward spring. Among three clones, KY08-1200 was less affected by chilling stress and presented a higher value of Fv/Fm up to the end of experiment. Considering these results, we concluded that the decreased chlorophyll content measured by the SPAD index was a simple indicator for screening chilling-tolerant clones.