ASSESSMENT OF FREEZE INJURY IN BOSKOOP GIANT BLACK-CURRANT BUDS

A seasonal study was conducted to assess the freezing injury of 'Boskoop Giant' black currant (Ribes nigrum L.) samples from Oct. 1991 through Mar. 1992. Buds were subjected to either differential thermal analysis (DTA) or one of a series of temperatures (0 to -36C). Freeze injury was then assessed either visually or with TTC. Results indicated that black currant floral buds have multiple low-temperature exotherms (LTE). Freeze injury in intact buds could not be visually quantified because of the lack of visible browning, nor assayed with TTC reduction. Excised floral primordia incubated in TTC, however, developed colored formazan following exposure to nonfreezing and sublethal freezing temperatures, but remained colorless when exposed to lethal temperatures. The percentage of floral primordia that were colored and colorless were tabulated and a modified Spearman-Karber equation was used to calculate the temperature at which 50% of floral primordia were killed (T50). The T50) temperature was correlated with the temperature at which the lowest LTE was detected (R2 = 0.62). TTC reduction assay using excised floral bud primordia was a good indicator of viability in frozen black currant buds. Chemical name used: 2,3,5-triphenyltetrazolium chloride (TTC).