Role of the cotyledonary tissue in improving low and ultralow temperature tolerance of butternut (Juglans cinerea) embryonic axes
1998
Beardmore, T. | Vong, W.
Butternut (Juglans cinerea L.) survival is threatened in North America by the fungus Sirococcus clavigignenti-juglandacearum. To date, there is no control for this fungal disease and long-term seed storage, to ensure survival of the species, is not a viable option. Initially, low (0, -5, -10, -15, and -40 degrees C) and ultralow (-196 degrees C, cryopreservation) temperature tolerance of butternut embryonic axes isolated from the nuts collected from one tree was examined. Embryonic axes with approximately 3 mm of cotyledonary tissue attached to the hypocotyl area germinated after exposure to 0, -5, -10, -15, and -40 degrees C for 4 h and to -196 degrees C for 24 h. Percent germination after exposure to 0 and -5 degrees C was 87 and 82%, respectively, and after -10 and -15 degrees C was 29 and 27%, respectively. Thirty-two percent of axes germinated after -40 degrees C, and 36% germinated after exposure to -196 degrees C. Tolerance to -196 degrees C was examined in the embryonic axes isolated from the nuts of 13 other trees. Significant tree-to-tree variation was found in the tolerance of the embryonic axes to low temperature. This variation corresponded to the water content of the embryonic axes; water contents of 4.8% and lower exhibited tolerance to -196 degrees C. Reducing the water content of the embryonic axes by slow desiccation to 4.8% or less resulted in an increased tolerance to -196 degrees C. These results suggest that low and ultralow temperature storage of embryonic axes may be a viable method for butternut ex situ conservation.
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