Desiccation studies of dormant buds from selected woody horticultural plant species

Several reports have demonstrated the advantages of backing up field maintained collections in liquid nitrogen. However, the application of cryopreservation protocols to the wide range of genetic diversity found in germplasm collections has only been reported in a few instances. Long-term preservation of dormant buds is less expensive than cryopreservation of shoot or meristem cultures; hence it presents an option for backing-up collections of woody plant species. Dormant bud cryopreservation procedures can be species dependent, but in general they require an ability of the buds to survive desiccation to ≤30% MC and slow-cooling (1°C/h) to -30°C prior to liquid nitrogen exposure. Therefore, this study looked at viability after desiccation to assess pre-liquid nitrogen survival of dormant buds from a number of species. Dormant branches were collected from field-grown trees, cut into 35 mm sections containing one dormant bud per stem section and desiccated to 35-40%, 30-35% and 25-30% MC. Bud sections were then rehydrated in moist peat moss and survival was evaluated by grafting. Data indicated that 65-100% of almond and apricot, >80% of sweet cherry, >21% of walnut and >12% of blueberry dormant buds survived desiccation to 25-30% MC. In contrast, pomegranate dormant buds did not survive desiccation to 25-30% MC suggesting other preservation methods may be applicable for this species. Dormant buds present a difficult experimental system due to many sources of variation which can confound results including the level of dormancy of the buds and the grafting step where success can depend on personnel doing the grafting as well as the source and variety of the rootstock. Development of dependable cryopreservation protocols would increase the number of woody plant accessions being backed up at our Center in a considerably shorter time than preserving the accessions via tissue culture material.