Supercooling and Extracellular Ice Formation in Differentiating -Buds of Eastern Thornless Blackberry

Abstract

`Hull Thornless' and `Black Satin' blackberry (Rubus spp.) canes were collected from Sept. 1989 through Mar. 1990 to determine the hardiness and supercooling characteristics of buds at various stages of development. Anatomical studies were also conducted to examine the location of ice voids in buds frozen to -5 or -30C. Differentiation of the terminal flower occurred in `Black Satin' buds by 6 Nov., whereas `Hull Thornless' buds remained vegetative until early spring. As many as nine floral primordia were observed in both cultivars by 12 Mar. The hardiness of the two cultivars was similar until February. Thereafter, `Black Satin' buds were more susceptible to cold injury than those of `Hull Thornless'. Flora1 and undifferentiated buds of both cultivars exhibited one to four low temperature exotherms (LTEs) from 9 Oct. to 12 Mar. in differential thermal analysis (DTA) experiments. The stage of flora1 development did not influence the bud's capacity to supercool. The number of LTEs was not related to the stage of floral development or to the number of floral primordia. Extracellular voids resulting from ice formation in the bud axis and scales were observed in samples subjected to -5 or -30C.