Cryotherapy Using Shoot Tip Cryopreservation
Jean Carlos Bettoni, Independent Researcher, 35 Brasil Correia Street, Videira, SC 89560510, Brazil<EMAIL_ADDRESS>Gayle M. Volk, USDA-ARS National Laboratory for Genetic Resources Preservation, 1111 S. Mason St., Fort Collins, Colorado 80521<EMAIL_ADDRESS>The purpose of this chapter is to describe the concept of shoot tip cryotherapy—the application of shoot tip cryopreservation to eradicate pathogens.
Outline
- Introduction
- Principles of shoot tip cryotherapy
- Development of shoot tip cryotherapy procedures
- Regrowth and pathogen detection
- Efficacy of cryotherapy
- Conclusions
- References
- Acknowledgments
1. Introduction
Most fruit and nut cultivars, as well as some root and tuber vegetables and sugar crops, are vegetatively propagated to maintain their specific genetic combinations. New plants that are identical to the initial plant are produced by grafting, rooted cuttings, runners, rhizomes, tubers, etc. (Figure 1). If stock plants harbor diseases, those pathogens might be transmitted to the offspring when infected materials are vegetatively propagated, and this represents a major constraint for crop production. Infected plants usually have reduced yields and an increased susceptibility to other pathogens. Moreover, the presence of pathogens limits the safe movement of plant materials across borders. Propagating clean, pathogen-free stock plants is the most effective and sustainable strategy to control the presence and spread of viruses in the field. Improved methods for producing disease-free plants are therefore needed to control the spread of pathogens (Rubio et al., 2020; Barba et al., 2017).
Figure 1. Examples of propagation methods: A) apple grafting, B) strawberry runners, C) garlic bulbs, D) potato tubers. Photo credits: Remi Bonnart (A), G. Volk (B,C), and USDA (D).
Tender 1–2 mm shoot tips can survive liquid nitrogen (LN) storage if processed with optimized cryopreservation protocols. When the shoot tips are derived from infected plants, a percentage of the plants recovered after LN exposure will not harbor the pathogens that were in the source plant. This process of eliminating pathogens is termed cryotherapy. Cryotherapy has been used to eliminate viruses, viroids, phytoplasma, and bacteria from plant materials. Shoot tip cryotherapy is transitioning from primarily a research effort to a more prevalent method in pathogen elimination operations (Wang et al., 2022). Detailed information about shoot tip cryotherapy for pathogen eradication can be found in multiple reviews (Wang and Valkonen, 2009; Zhao et al., 2019; Bettoni et al., 2021; Wang et al., 2022).
2. Principles of shoot tip cryotherapy
Shoot tip-based pathogen elimination methods depend on pathogens preferentially residing in certain cells. Many pathogens, including most viruses, are absent from the undifferentiated cells in the apical dome of the meristem. Cells in the apical meristems are smaller in size, have smaller v