English walnut rootstocks help avoid blackline disease, but produce less than ‘Paradox’ hybrid

Abstract

While 'Paradox' hybrid seedlings are often the rootstocks of choice for California walnut (Juglans hindsii) orchards, there is a resurgence of interest in using English walnut (Juglans regia) seedlings because walnut blackline disease, which is endemic in many California walnut production districts, does not affect them. We compared the growth and productivity of walnuts on English rootstocks from a variety of sources to those on Paradox rootstock. Two trials were established near Linden in San Joaquin County, California. Site 1, established in 1989, consisted of 3 rows of Chandler trees that had been grafted on seedlings of English walnut cultivars Manregian, Eureka, Ronde de Montignac, Corne and a source collected from Tarragona, Spain. Site 2, established in 1994, included seedlings of Eureka, Waterloo, Chandler, Sunland, Russia, Carpathian and Paradox hybrid. The growth and productivity of Chandler walnut trees were similar among trees on seedling English rootstocks in one trial, but trees on English rootstocks were smaller and had lower production than Paradox hybrid-rooted trees in the other.