Rooting ability of Persian walnut as affected by seedling vigour in response to stool layering

Summary

Walnut (Juglans regia L.) is an important nut crop with a “difficult-to-root” characteristic. In this study, the rooting ability of low-vigour and precocious seedlings of 3-year-old Persian walnut was compared with semi-vigorous and high-vigour seedlings using the stool layering method. The results indicated that low-vigour seedlings rooted more (40%) than semi-vigorous (31.42%) and high-vigour (17.14%) seedlings. The average number of roots per shoot (layer) and rooting score (on a scale of 1 – 5) in the low-vigour group were 7.83 and 4.19, respectively, which differed significantly from the high-vigour group. Moreover, most of the high quality adventitious roots formed on low-vigour seedlings appeared to originate from internal tissues compared to the low quality and brittle roots that originated from callus in high-vigour seedlings. Improved rooting of low-vigour seedlings, together with a significant negative correlation between layer size and root number (r = –0.29), reflects substantial structural or hormonal differences among seedlings of different vigour. Approx. 70% of rooted layers survived after transferring to field condition. Our results provide more support for the possibility of vegetative propagation of walnut by conventional stool layering, as well as the selection of easy-to-root, dwarf walnut cultivars or rootstocks on their own roots.