Antimicrobial forcing solution improves recovery of cryopreserved temperate fruit tree dormant buds

Dormant bud cryogenic preservation is a cost- and labor-efficient method of genetic resource backup compared to in vitro derived meristem shoots cryopreservation. While protocols have been developed for cryopreserving apple dormant buds, effective and reproducible protocols are yet to be developed for several temperate fruit and nut species. Dormant bud cryopreservation typically requires material to be grafted to evaluate viability and recover a plant. Forced bud development has been used on a very limited scale for cryostored dormant budwood recovery, however, it provides a labor-efficient alternative viability assessment. To increase the utility of this approach, regrowth must be optimized to allow complete plant recovery. We hypothesized that bacterial attacks are limiting regrowth, thus, an antimicrobial forcing solution can maximize regrowth potential. This study examined the effects of an antimicrobial forcing solution (8-hydroxyquinoline citrate and sucrose, 8-HQC) on the cryosurvival and recovery of dormant buds of fruit (Malus x domestica, Prunus armeniaca, Prunus avium, Prunus persica, Pyrus communis), and nut species (Juglans regia, Juglans nigra, Juglans microcarpa). Recovery and shoot development were significantly improved for all the fruit and one nut species (J. microcarpa) treated with the 8-HQC, compared to standard recovery under high humidity alone (P < 0.001). Additionally, this post cryo recovery approach led to successful in vitro shoot tip establishment across all surviving fruit species. 8-HQC embedded forced bud development method increased viability and efficiency for existing cryostored material and can be used as a benchmark to develop protocols for different crops that could potentially lead to complete plant recovery.