Survival of cryogenically-stored dormant apple buds: A 20 year assessment

Authors: Walters, Christina; Volk, Gayle; TOWILL, LEIGH - Retired ARS Employee; Forsline, Philip

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/13/2009
Publication Date: 4/13/2009
Citation: Walters, C.T., Volk, G.M., Towill, L., Forsline, P.L. 2009. Survival of cryogenically-stored dormant apple buds: A 20 year assessment. I International Symposium on Cryopreservation in Horticultural Species, April 5-8, 2009. Leuven, Belgium. pp. 25. Meeting abstract.

Interpretive Summary: Cryobiologists assume that the extreme low temperatures of liquid nitrogen stop chemical and physical reactions that lead to sample aging and loss of viability. This assumption, based on extrapolations of temperature – reaction kinetic relationships, is not completely supported by accumulating evidence that dried seeds can deteriorate during cryogenic storage. After 30 years of cryogenic storage, seeds of some species exhibited quantitatively lower viability and vigor. In this paper, we ask whether loss of viability also occurs in cryogenically stored dormant buds of apple. The same thermodynamic models used for seeds apply to apple buds, suggesting the possibility that decline may occur within decades rather than centuries. Evaluating the empirical evidence of long term survival of apple buds is difficult because of the numerous sources of variation that confound viability assessments. Survival of buds dried to 25-30% water (fresh weight basis), slowly cooled to -30oC and then plunged into liquid nitrogen varies with genetic line, month of harvest and year of harvest. Viability assessments use budding techniques, which rely on consistency and skill of the grafter. Many of these variables were controlled in a 15 year long experiment in which the same eight genotypes were harvested yearly, cryogenically stored, and periodically evaluated for survival. For the most part, apple buds survived cryostorage. However, there are some indications of change in survival that may arise from uncontrolled experimental variation or deterioration during storage. Cryogenic storage of dormant buds is a highly efficient way to back up orchard collections, but assumptions about the power of crygenics to prevent change in biological material must still be viewed with some caution.

Technical Abstract: Cryobiologists assume that the extreme low temperatures of liquid nitrogen stop chemical and physical reactions that lead to sample aging and loss of viability. This assumption, based on extrapolations of temperature – reaction kinetic relationships, is not completely supported by accumulating evidence that dried seeds can deteriorate during cryogenic storage. After 30 years of cryogenic storage, seeds of some species exhibited quantitatively lower viability and vigor. In this paper, we ask whether loss of viability also occurs in cryogenically stored dormant buds of apple. The same thermodynamic models used for seeds apply to apple buds, suggesting the possibility that decline may occur within decades rather than centuries. Evaluating the empirical evidence of long term survival of apple buds is difficult because of the numerous sources of variation that confound viability assessments. Survival of buds dried to 25-30% water (fresh weight basis), slowly cooled to -30oC and then plunged into liquid nitrogen varies with genetic line, month of harvest and year of harvest. Viability assessments use budding techniques, which rely on consistency and skill of the grafter. Many of these variables were controlled in a 15 year long experiment in which the same eight genotypes were harvested yearly, cryogenically stored, and periodically evaluated for survival. For the most part, apple buds survived cryostorage. However, there are some indications of change in survival that may arise from uncontrolled experimental variation or deterioration during storage. Cryogenic storage of dormant buds is a highly efficient way to back up orchard collections, but assumptions about the power of crygenics to prevent change in biological material must still be viewed with some caution.