Persian walnut ( Juglans regia L.) is widely cultivated for nut and wood production ( McGranahan and Leslie, 2012 ). Originally cultivated on Persia’s plateau, it has been introduced worldwide ( Bernard et al. 2018a ). In addition to morpho
performance ( Bonhomme et al., 2005 , 2010 ; Lacointe et al., 2004 ). As persian walnut orchards are long-term investments, mediating the effects of winter temperature changes may become a major task for orchard management in the near future ( Melke, 2015
purpose of this research was to evaluate the use of gamma-irradiated pollen for production of parthenogenetic haploid plants in persian walnut. Viability of irradiated pollen, percent fruit set, parthenogenetic embryos formation, and the first production
Phytophthora crown and root rot (PCRR) is among the most serious diseases of Persian walnut worldwide. In California, more than 10 species of Phytophthora have been implicated in the disease, but Phytophthora cinnamomi and P. citricola are
the chilling requirement of walnut cultivars between 400 and 1500 h below 7 °C. Table 1. Chilling requirement of Persian walnut cultivars and genotypes (hours below 7 °C) to reach 50% of lateral and terminal buds and catkins to the balloon or green tip
The Persian or English walnut (Juglans regia) is widely cultivated, with commercial production in France, Italy, Turkey, China, and the United States. Practically all of the U.S. production of Persian walnuts is in the central valley of California, which now has about 169,000 bearing acres with an average yield of around one and one-third short tons per acre. Many orchards produce over two tons, and three tons per acre are common in many modern plantings. Walnuts have two major outlets: the exported in-shell market (about 35% of production) and the domestic shelled market (about 68% of production). A cooperative handles about half the crop, while several independent handlers sell the remainder. Walnuts are sensitive to both low and high temperatures. Temperatures in excess of 90 °F will begin to sunburn nuts. Freezing temperatures will damage tender growth in the spring and fall. Dormant trees can tolerate 15 °F without injury if soils are moist. Dry winter soils and cold temperatures cause winter kill. A minimum of 800 hours of winter chilling are required to avoid delayed bud break and poor crops. Walnuts do best on deep, medium textured, well drained soil. Under these conditions, both rootstocks, the Northern California Black Walnut (J. hindsii) and Paradox (J. regia x J. hindsii), do well. Under less favorable soil conditions, Paradox is the preferred rootstock. A mature walnut orchard requires 4 to 4.5 acre-feet of water per acre per year if the trees are to produce the maximum number of high quality nuts possible. Hartley, preferred for its in-shell quality, is the leading cultivar, with about 30% of the acreage. In recent years, the Chandler variety has accounted for most new plantings. It is known for high kernel quality and yields. Yield factors include: bearing habit, bearing area, flower differentiation, fruit set, nut size, kernel percentage, and kernel quality. Major insect pests of walnut include codling moth, navel orangeworm, and walnut husk fly. The major diseases are walnut blight, deep bark canker, Phytophthora, and blackline. Major research efforts include the walnut breeding program, which includes blackline and Phytophthora susceptibility of new cultivars and root-stocks, codling moth and walnut husk fly control, epidemiology and control of walnut blight, pruning and planting strategies, and clonal propagation.
. 2009 Estimation of chilling and heat requirement of some Persian walnut cultivars HortScience 44 697 701 Bartolozzi, F. Fontanazza, G. 1999 Assessment of frost tolerance in olive Sci. Hort. 81 309 319 Bierman, J. Stushnoff, C. Burk, M.J. 1979
Abstract
In vitro propagation of mature cultivars of Juglans regia L. (Persian or English walnut) could have several major advantages over propagation by grafting on seedling black walnut [J. hindsii (Jeps.) Jeps.] rootstock. If commercial cultivars perform satisfactorily on their own roots, the expensive and time-consuming process of grafting could be avoided, genetic uniformity could be assured, and trees would not be subject to the lethal girdling of blackline disease (5). In addition, mature clones on their own roots might be more precocious than grafted seedlings. These factors are becoming increasingly important as walnut growers change to high-density or hedgerow orchards (D.E. Ramos, personal communication).
nut. Although China is considered one of the origin places of J. regia , the natural population is rare in China at present, most of them are landrace populations. Chinese walnut is one of the most widely distributed temperate deciduous native tree
, Univ. of California-Davis, for advising and reviewing the analysis, and we thank the Ministry of Science, Research, and Technology of Iran, the Univ. of Tehran, and the Walnut Marketing Board of the United States for supporting the stay of Kourosh