EXTENDING THE DORMANT BUD CRYOPRESERVATION METHOD TO NEW TREE SPECIES

In cryopreservation of germplasm, using dormant winter buds (DB) as source plant material is economically favorable over tissue culture options. Although the DB cryopreservation method has been known for many years, the approach is feasible only for cryopreserving a select number of temperate tree species. The original method developed for Malus (apple) DB, requires desiccation of stem segments (to 25-30% moisture content), slow cooling (to -30°C), storage in liquid nitrogen vapor (LNV) and viability testing by grafting. We investigated the possibility of using this method for cryopreservation of DB of Juglans regia, J. cinerea, Prunus dulcis, P. persica, Salix exigua and S. triandra germplasm. The post LNV viability of P. dulcis, P. persica and S. triandra DB was very low. Dormant buds of J. cinerea harvested in December were viable in a higher percent than buds harvested in January. The fraction of viable Salix DB on 10 cm branch segments was significantly higher (30 and 80%) than on 6 cm long segments (0 and 45%; P<0.05); this indicated that the longer segments might be more suitable for cryopreservation of the two Salix species. For Juglans regia, the viability after LNV exposure was evaluated by grafting and forced bud break under high relative humidity conditions and the percent of viable buds was similar for both methods; hence testing under mist might be a valid indication of viability. The application of the Malus DB cryopreservation method might also be applicable to preservation of almond, peach and English walnut however studies on factors enhancing post LNV viability are needed.