Selection Methods and Key Points for Walnut Rootstock Types in Walnut Seedling Cultivation
Currently, the process of improving walnut varieties in China is relatively fast, and most regions have already achieved the use of grafting methods to propagate seedlings. The commonly used rootstock types include 5 kinds: common walnut, iron walnut, wild walnut, Manchurian walnut, and Chinese wingnut.
As shown in the picture: walnut
1. Common walnut. The walnuts produced in northern China are almost all common walnuts. Using common walnut as rootstock to graft improved walnut varieties (except bubble walnut), it is customarily called "common rootstock" or "own rootstock". It is widely used in walnut-producing areas in northern China. Generally, varieties with poorer quality such as clamp walnut or soft-shell walnut are used, not early-fruiting thin-shell walnuts. This rootstock has strong affinity, the graft union heals easily, the grafting survival rate is the highest, and the seedlings grow vigorously, with good growth and fruiting, and no premature fruiting phenomenon occurs. At the same time, common walnut as rootstock also has resistance to blackline disease.
2. Iron walnut. Commonly used in Yunnan and Guizhou provinces, with a relatively long history of application. It is two types of the same species as bubble walnut. The nut shell is thick and hard, and the kernel yield is low (20% ~ 30%), so it is generally not used as a fruit. The survival rate of grafting bubble walnut is high. It is the rootstock for excellent varieties such as bubble walnut, Niangqing walnut, Santai walnut, Dabai shell walnut, and Xixiang walnut, and is tolerant of hot and humid climates. However, it is not tolerant of severe cold, so it is not suitable for use in northern regions.
3. Wild walnut. Mainly distributed in Jiangsu, Hubei, Shaanxi, Sichuan, Gansu and other provinces. It has good grafting affinity and is suitable for the rainy and highly humid climate conditions of the south.
4. Manchurian walnut. It is cold-resistant, drought-resistant, and tolerant of barren soil. It is the most cold-resistant species in the genus Juglans and can be used as a cold-resistant rootstock for common walnut to expand the cultivation range. It is suitable for Northeast, North China, and Northwest China. Its affinity is not as good as that of common walnut, and both the grafting survival rate and preservation rate are lower than those of walnut own rootstock.