Cultivar Influences Early Rootstock and Scion Survival of Grafted Black Walnut

Abstract

Black walnut (Juglans nigra L.) is being increasingly planted and cultivated in the midwestern USA for the economic potential of both its wood and nuts. Trees that are established for nut production have greater potential for long-term productivity and profit if they are grafted to superior nut-producing cultivars. While numerous productive cultivars have been identified that perform well as scions, advances have not yet been made toward developing superior black walnut rootstocks. Furthermore, very little is known about how various black walnut scion or rootstock cultivars may interact with each other and their environment. The objective of this study was to evaluate early transplant performance of black walnut scion-rootstock combinations at four sites, and to determine which cultivars or cultivar-graft combinations may be best for successful establishment of new plantings. A total of 327 trees comprising 20 different black walnut scion-rootstock graft combinations transplanted at four locations in Missouri (spring 2001) and Arkansas (fall 1999) were selected for analysis. All trees were pre-grafted, and consisted of potted two-year-old seedling rootstocks of known female parentage (open-pollinated seeds from named cultivars), and one-year-old scions of superior, named nut-producing cultivars. Rootstock and scion survival at all sites was assessed in fall 2002. Seedlings from the cultivar ‘Kwik-Krop’ survived significantly better as rootstocks (83%) than did seedlings from ‘Sparrow’ (51%), ‘Thomas’ (57%), and an unimproved nursery-run rootstock (65%), but rootstock source did not affect survival of specific scion cultivars. Among trees on surviving rootstocks, ‘Kwik-Krop’ scions survived better (96%) than did ‘Surprise’ (79%) or ‘Emma K’ (80%) scions. Over the entire range of rootstocks, trees with ‘Thomas’ scions had better rootstock survival (79%) than ‘Sparrow’ (63%), ‘Kwik-Krop’ (63%), and ‘Surprise’ (53%) scions. These results suggest that rootstock seed source is an important consideration for successful establishment of grafted black walnut plantings, and that scion cultivar might also influence early transplant survival.