PERSPECTIVE: Indian citrus germplasm in the frozen state: conserving exceptional genetic diversity for posterity, utilization and food security

India has a rich genetic diversity of citrus, both cultivated and wild types, particularly in the northeastern and northwestern regions. Managing genetic resources of this enormous diversity is a challenging task. Citrus species show non-orthodox seed storage behavior and, therefore, are not easily conserved using conventional −20°C storage methods. Cryopreservation is the only feasible long-term ex situ conservation strategy of a diverse genus like citrus. This strategy not only protects valuable genetic material against threats such as diseases, climate change, and habitat loss, but also facilitates future research and breeding efforts to develop resilient and high-yielding citrus varieties. Although germplasm collection and conservation of citrus began >100 years ago, the long-term ex situ conservation of citrus genetic resources accelerated from the 1990s with the establishment of the cryogenebank at ICAR-National Bureau of Plant Genetic Resources, New Delhi, India. During the last three decades, germplasm of citrus has been collected from various parts of the country and protocols to cryopreserve seeds, embryos, embryonic axes and pollen have been successfully developed. The base collection of citrus germplasm at the National Cryogenebank has cryopreserved embryos and embryonic axes through different techniques, namely desiccation-fast freezing, encapsulationdehydration, vitrification, or encapsulation-vitrification. Basic studies on seed physiology and storage behavior of diverse citrus species have been conducted, resulting in the successful development of cryopreservation protocols. These advancements have facilitated the cryobanking of over 1,245 accessions from 39 species of Citrus and of the related genus Poncirus in the National Cryogenebank.