Progress of collection, conservation and innovative utilization of walnut resources in the National Walnut and Chestnut Germplasm Repository (Tai’an)

Walnut, a deciduous fruit tree in temperate regions, belongs to the genus Juglans in the family Juglandaceae. The genus Juglans, comprising approximately 23 species, is widely distributed throughout the world. The distribution range of walnut covers Asia, Europe, North America, South America, Oceania, and parts of Africa. There are significant morphological differences among various varieties. Plants of this genus have edible, medicinal, and material values. Walnut kernels are rich in nutrients, containing various plant proteins, fats, trace elements, and vitamins. China is rich in walnut germplasm resources and is one of the origin and distribution centers of the genus Juglans. There are five species native to China, namely, Common walnut (J. regia L.), Manchurian walnut (J. mandshurica Max), Wild walnut (J. cathayensis Dode), Ma walnut (J. hopeiensis Hu), and Iron walnut (J. sigillata Dode). China has a long history of cultivation, and its cultivation area and yield rank first in the world. In the future, China's walnut industry needs to optimize its variety structure further, promote green technology, and tap the potential of high-value by-products to consolidate its position as the world's largest producer. China's walnut germplasm resources are vibrant, which provides a solid foundation for the development of the walnut industry. China has established several national and provincial walnut germplasm repositories, including the Walnut Germplasm Resources Repository of Yunnan Academy of Forestry and the Walnut Germplasm Resources Repository of Hebei Province, which have preserved a large amount of germplasm resources. These databases provide essential basic data for walnut breeding and industrial development by collecting, preserving, identifying, and evaluating information. In terms of breeding and popularization, many new walnut varieties with high yield, high quality, and disease resistance were cultivated through cross- breeding and marker- assisted selection. For example, varieties such as Xiangling, Wen 185, Zhonglin series, Liaohe series, and Yunxin series have demonstrated excellent performance in terms of yield, quality, and disease resistance, and have been widely promoted and planted across the nation. In recent years, the breeding and popularization of early fruiting walnut varieties have significantly increased the early yield and economic benefits of walnut. The genetic diversity and functional genes of walnut germplasm resources were analyzed by genomics, transcriptomics, and metabolomics to provide theoretical support for molecular breeding. For example, genome sequencing technology has revealed the origin of allopolyploidy and the changes in the evolutionary rate of walnut species. In the future, it is necessary to collect and preserve additional wild walnut germplasm resources, explore their disease resistance, stress resistance, and high-yielding genes, and provide more highquality resources for breeding. To explore the application potential of walnut germplasm resources in functional foods, medicine, and materials science, we must improve resource utilization efficiency. The National Walnut and Chestnut Germplasm Repository (Tai’an) is one of the most significant repositories for preserving walnut germplasm resources in China. By December 2024, 450 walnut germplasm resources had been collected and preserved, facilitating the optimization of walnut varieties and industrial upgrading. This effort played a crucial role in alleviating rural poverty and promoting prosperity, as well as industrial revitalization. Basic research on walnut quality and disease resistance has promoted the promotion of excellent walnut varieties and industrial upgrading. This paper reviews the development history of the National Walnut Germplasm Repository (Tai’an), summarizes the current situation of collection and conservation of walnut germplasm resources in recent decades, and the achievements of innovative utilization of walnut germplasm resources, and prospects the future research direction, to provide reference and guidance for the efficient utilization and industrial development of walnut germplasm resources in the future.