How applicable are dormant buds in cryopreservation of horticultural woody plant crops? The Malus case

Using dormant buds (DB) for germplasm cryopreservation was published few decades ago and since then, dormant buds have been used to preserve genetic resources of selected horticultural woody plant species. The advantages of employing DB in preservation are widely known; the most relevance is no requirements of aseptic cultures, high processing throughput and involvement of a relatively low skilled technical support; but the method has also shortcomings, such as seasonality of processing and lack of procedural modifications that might support preservation of all accessions in a collection. The US, NLGRP cryopreserved DB of 2168 unique Malus (Mill.) accessions (among 51 species) with a ≥40% post cryo viability. The method worked well for all accessions in 20 species, for ≥90% of accessions in six species and at a various percent (0-89%) in the remaining 25 species. For species with the largest number of processed accessions, the M. domestica, Borkh., M. hybrid and M. sieversii (Ledeb.) M. Roem. (1355, 326 and 128 cryopreserved accessions, respectively), the percent of accessions responding favorable to the DB method was high (96, 96 and 82%). The results indicated variability in Malus DB response to liquid nitrogen exposure; similar results were recorded in the Pyrus L. collections. Procedural refinements of the DB cryopreservation method could increase the method applicability to a much higher number of Malus species and its use in other collections of horticultural woody plants like Prunus L. and Pyrus L.