ASSESSMENT OF FREEZE INJURY IN BOSKOOP GIANT BLACK-CURRANT BUDS

A seasonal study was conducted to assess the freezing injury of 'Bosko op Giant' black currant (Ribes nigrum L.) samples from Oct. 1991 throu gh Mar. 1992. Buds were subjected to either differential thermal analy sis (DTA) or one of a series of temperatures (0 to -36C). Freeze injur y was then assessed either visually or with TTC. Results indicated tha t black currant floral buds have multiple low-temperature exotherms (L TE). Freeze injury in intact buds could not be visually quantified bec ause 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 temp eratures, but remained colorless when exposed to lethal temperatures. The percentage of floral primordia that were colored and colorless wer e tabulated and a modified Spearman-Karber equation was used to calcul ate the temperature at which 50% of floral primordia were killed (T50) . The T50) temperature was correlated with the temperature at which th e lowest LTE was detected (R2 = 0.62). TTC reduction assay using excis ed floral bud primordia was a good indicator of viability in frozen bl ack currant buds. Chemical name used: 2,3,5-triphenyltetrazolium chlor ide (TTC).