Cryopreservation is considered an ideal strategy for the long-term preservation of plant genetic resources. Significant progress was achieved over the past several decades, resulting in the successful cryopreservation of the genetic resources of diverse plant species. Cryopreservation procedures often employ in vitro culture techniques and require the precise control of several steps, such as the excision of explants, preculture, osmo- and cryoprotection, dehydration, freeze-thaw cycle, unloading, and post-culture for the recovery of plants. These processes create a stressful environment and cause reactive oxygen species (ROS)-induced oxidative stress, which is detrimental to the growth and regeneration of tissues and plants from cryopreserved tissues. ROS-induced oxidative stresses were documented to induce (epi)genetic and somatic variations. Therefore, the development of true-to-type regenerants of the source germplasm is of primary concern in the application of plant cryopreservation technology. The present article provides a comprehensive assessment of epigenetic and genetic integrity, metabolic stability, and field performance of cryopreserved plants developed in the past decade. Potential areas and the directions of future research in plant cryopreservation are also proposed.

In vitro micrografting is an important technique supporting the micropropagation of a range of plant species, particularly woody plant species. Over the past several decades, in vitro micrografting has become a strategy to facilitate shoot recovery and acclimatization of in vitro-grown horticultural species. This review focuses on studies on horticultural crops over the past two decades that cover the establishment of in vitro micrografting, discusses factors affecting the success of in vitro micrografting, and provides commentary on the contribution of micrografting applications to the field of micropropagation. Considering the important roles of micrografting in the restoration of vigor and rooting competence, in promotion of shoot recovery following somatic embryogenesis and organogenesis, and in facilitation of shoot regrowth after cryopreservation, the potential use of this technique in facilitation of genetic engineering and safe conservation of horticultural species are specially highlighted.

Root and tuber crops (RTCs) are the second-most important carbohydrate commodity after cereals. Many species of the RTCs are vegetatively propagated, making their shoot tips the preferred material to be conserved for future uses. Shoot tip cryopreservation provides an important tool to support the long-term conservation of plant genetic resources. Over the past four decades, significant efforts have been undertaken to move shoot tip cryopreservation of RTCs from research projects to full-scale implementation in cryobanks. This comprehensive review focuses on the history of cryopreservation protocols developed in RTCs. The encapsulation and vitrification solution-based cryopreservation techniques followed by ultra-rapid freezing and thawing have been highly successful. Additionally, different strategies for improving the cryotolerance of shoot tips have been introduced to further increase post-cryopreservation recovery. Finally, the research conducted to explain the mechanism underlying cryoprotection and differential cryotolerance including the use of histological studies are highlighted.

Preservation of plant virus is a fundamental requirement in all types of virus-related research and applied applications. Development of efficient, reliable strategies for long-term preservation of plant virus would largely assist these studies. The present study reported a novel biotechnology allowing cryopreservation of Apple stem grooving virus (ASGV) in living shoot tips. Following cryopreservation by droplet-vitrification or encapsulation-dehydration, about 62–67% of shoot regrowth and 100% of ASGV cryopreservation were obtained. Although shoot proliferation and virus concentration were reduced in cryopreserved diseased shoots after 8 weeks of shoot regeneration, continuous subculture for 4 times (16 weeks) increased shoot proliferation and virus concentration to comparative levels as those produced by shoot tip culture (as a control to shoot tip cryopreservation). Cryopreserved ASGV was efficiently transmitted to a woody plant by micrografting and to a herbaceous indicator by mechanical inoculation. Gene sequencing in three fragments of ASGV genome including coat protein and movement protein showed that cryopreserved ASGV shared 99.87% nucleotide identities with shoot tip culture-preserved virus, indicating cryopreserved virus is genetically stable. The present study demonstrates ASGV, a representative virus that can infect meristematic cells of shoot tips, can be efficiently cryopreserved in shoot tips. To the best of our knowledge, this is the first report on plant virus cryopreservation in living tissues, and has great potential applications to long-term preservation of plant viruses.

In vitro tissue culture technologies provide novel tools for improving plant production