Mature hedgerow walnut trees (Juglans regia L. cv. Chico) were irrigated at rates of 33, 67, and 100% of potential orchard ETc (about 350, 700, and 1050 mm/season, respectively) for three years. All trees were then returned to 100% ETc for the subsequent three year period.
Deficit irrigation reduced vegetative growth as measured by shaded area of the orchard floor and trunk growth. Yield reductions, which were minimal after one season, were significantly greater in years two and three. However, the relationships between crop yield and applied water were linear for all deficit irrigation seasons. Upon a return to full irrigation, trunk (and presumably shoot) growth of the previously stressed trees accelerated to levels greater than the control. The subsequent increase in fruiting positions resulted in a return to full production after two years. This suggests that hedgerow walnuts have the potential to recover rapidly from drought-induced production losses if no secondary effects of tree water stress, such as disease or pests, occur.
The objective of this work was to determine the chilling and heat requirements of Persian walnut cultivars and genotypes using excised twigs. The experiment was carried out from Nov. 2006 and 2007 to Mar. 2007 and 2008. One-year-old twigs were prepared from four cultivars and four domestic genotypes of Juglans regia L. After leaf fall, the twigs were taken and placed in plastic bags and kept at 4 ± 1 °C to stimulate 400 to 1500 chilling hours. After chilling, the excised twigs were transferred to the greenhouse with a natural photoperiod and a temperature from 18 to 27 °C. The evaluation of budbreak was made three times a week and the number of accumulated growing degree hours (°C) was determined until the buds reached the balloon or green tip stage. The chilling requirements were lowest (400 h) for catkins and highest (1000 h) for lateral buds. The Serr cultivar and ‘Z30’ genotype had the lowest chilling requirements (650 and 650 h). ‘Lara’, ‘Z63’, ‘Z53’, ‘Pedro’, and ‘Z67’ showed intermediate chilling requirements with values of 900, 900, 800, 750, and 750 h, respectively. Finally, ‘Hartley’ completed its dormancy after an accumulation of 1000 h, being the walnut cultivar with the highest chilling requirement in our study. As the final result, the cultivars and genotypes were classified into three groups based on their heat requirements: low requirement (‘Z30’ and ‘Serr’), medium requirement (‘Z53’, ‘Z67’, ‘Lara’, and ‘Pedro’), and high requirement (‘Hartley’ and ‘Z63’).
We investigated the basis for fruit drop in walnut (Juglans regia L.) following bloom period applications of streptomycin as a potential control treatment for walnut blight, a bacterial disease incited by Xanthomonas campestris pv. juglandis (Pierce) Dye. Experiments were conducted on streptomycin-treated field plots of `Vina' walnut. Four streptomycin treatments were applied at different times relative to anthesis. Fruit from all treatments grew similarly for four weeks following anthesis when high levels of fruit abscission began to occur in the treatment sprayed during the bloom period. Microscopy revealed that in this treatment ovules failed to develop normally, and neither embryo nor endosperm developed. The pattern of fruit development and timing of fruit drop following streptomycin treatment at bloom is similar in all ways to that of unpollinated walnut flowers where growth appears normal until abscission occurs 3 to 5 weeks after anthesis. Pollen germination and pollen tube growth were inhibited in the bloom-period treatments. Pollen germination in vitro was not affected by addition of streptomycin to a germination medium. If streptomycin were to be used in a walnut blight control program, application timed to coincide with the period of pistillate bloom and pistillate flower receptivity should be avoided.
Concentrations of N, P, K, Ca, Mg, B, Fe, Cu, Zn, and Mn in mature commercial fig (`Calimyrna'; `Sari Lop') leaves are presented throughout the growing season. These data can be used as preliminary norms for the interpretation of tree nutrient status for high-yielding commercial fig orchards. In comparison with other deciduous tree crops growing in the same regions {almond [Prunus amygdalus Batsch syn. P. dulcis (Mill) D.A. Webb], walnut (Juglans regia L.), peach [Prunus persica (L.) Batsch]}, productive fig trees have relatively low leaf N, P, and K concentrations (2.1%, 0.1%, and 1.0% dry weight, respectively) in July, although tissue Mn and Ca concentrations often exceed those typically found in other deciduous species growing in the same soils. Seasonal variations in fig leaf nutrient concentrations are similar to those of other tree crops. Marked declines in tissue K and N concentrations toward the end of the season may indicate a need for supplemental N and K fertilization in highly productive orchards. The potential for K deficiency in fig also is indicated by the generally lower leaf K concentrations in the low-vigor orchards examined.
English walnut (Juglans regia) producers in California compete with many insect and disease pests to produce an acceptable crop. Traditional control strategies work reasonably well for most pests. However, environmental concerns, loss of certain pesticides and new or impending regulations threaten the use of many traditional techniques for control of many of the pests. Codling moth (Cydia pomonella), walnut husk fly (Rhagoletis completa), and walnut aphid (Chromaphis juglandicola) are the major insects that affect California walnut production. Control strategies that use integrated pest management programs, beneficial insects, mating disruption, insect growth regulators, improved monitoring techniques and precise treatment timing based on the insect's life cycle are leading edge techniques currently available for insect control in walnuts. Major diseases include walnut blight (Xanthomonas campestris pv. juglandis), crown gall (Agrobacterium tumefaciens) and crown and root rot (Phytophthora spp). Both copper resistant and copper sensitive strains of the walnut blight bacterium are best controlled with combinations of copper bactericides and maneb instead of copper materials alone. A new computer model, Xanthocast, used to forecast the need for walnut blight treatment is under evaluation. Crown gall is managed using a preplant biological control agent and a heat treatment to eradicate existing galls. Phytophthora crown and root rot is dealt with primarily by site selection, irrigation management and rootstock selection.
The characteristics and mechanisms of foliar Zn uptake and translocation in pistachio (Pistachio vera L.) and walnut (Juglans regia L.) were investigated using 68Zn labelling in both intact and detached leaves. Following washing, mature walnut and pistachio leaves retained 8% and 12% of the total Zn applied, respectively. About half of retained Zn (3.5% and 6.5% of total Zn respectively) was absorbed into the leaf and translocated outside the treated area. Leaf age affected the Zn absorption capacity of pistachio but not walnut. Immature pistachio leaves absorbed more Zn than mature leaves. The absorption of Zn by walnut leaves at high concentrations (7.5 to 15 mm Zn) was not significantly affected by the pH of the solution. In pistachio Zn absorption was greatest at pH 3.5 and declined as pH increased to 8.5. The uptake process was not affected by light or addition of metabolic inhibitors. Foliar leaf absorption was only slightly affected by changes in temperature with an average Q10 of 1.2 to 1.4. This study suggests that foliar Zn uptake is dominated by an ion exchange and/or diffusion process rather than an active one. This study also demonstrates the usefulness of stable isotope labelling in studies of foliar Zn absorption.
The role of pollen in abscission of pistillate flowers of Persian walnut (Juglans regia L.) cv. Serr was investigated over a 4-year period by controlled pollinations and pollen counts. Self-pollen, pollen from other walnut selections or cultivars, or dead pollen was applied at high and low doses to pistillate flowers enclosed in pollination bags. Unbagged, open-pollinated flowers and bagged, nonpollinated flowers served as controls. In all cases, presence of pollen significantly increased the probability of pistillate flower abscission (PFA). Dead pollen resulted in as much PFA as live pollen. Counts of pollen grains confirmed that PFA-type flowers had significantly more pollen than normal flowers. In the fourth year `Serr' pollen was applied to unbagged flowers of `Serr' and ten other Persian walnut cultivars, and the amount of PFA on the artificially pollinated flowers was significantly higher than on the open-pollinated flowers, while the control flowers dusted with talc or pine pollen had almost no PFA. These results clearly indicate that excess pollen is involved in pistillate flower abscission in `Serr' walnut and suggests that other cultivars may also be sensitive to pollen load. This phenomenon may have implications in the biology of selfing and evolution.
In vitro rooting of three commercial cultivars of Persian walnut (Juglans regia L.), `Sunland', `Chandler', and `Vina', was examined using a two-phase rooting procedure: root induction in the dark on Murashige and Skoog (MS) medium with 15 μm IBA followed by root development in the light on a mixture of one-quarter strength Driver Kuniyuki Walnut (DKW) basal medium and vermiculite (1:1.25, v/v). Rooting percentages were: `Sunland' (94%), `Chandler (55%), and `Vina' (27%). A positive relationship was observed between the vigor of cultivars and rooting ability, but shoot length did not affect rooting success. Rooting was optimum when shoots were cultured on root induction media for 6 to 8 days. Increasing the sucrose level in the root induction medium to 40 g·L-1 improved rooting, and shoots induced to root at 22 °C rooted more readily than those induced at 30 °C. Either increasing or decreasing the nitrogen level in the multiplication medium had a negative effect on rooting. Rooted walnut shoots often cease growth during acclimatization, resulting in shoot rosetting. Spray application of Promalin® (25 mL·L-1) caused buds to break and induced elongation of shoots. Chemical name used: indole-3-butyric acid (IBA).
Abstract
Heritabilities and phenotypic correlations among 18 traits of walnut (Juglans regia L.) were estimated from measurements obtained over 14 years from approx 200 families including a total of more than 2,000 offspring. Prior to this analysis the data were statistically adjusted to mitigate the seriously confounding effects of fluctuating annual climate on estimates of genotypic value. The heritabilities were then estimated by regressing the average performance of each seedling, during its 1st 2 years of production, on its mid-parent performance. Heritabilities are above 80 for leafing date, 1st shedding of pollen, receptive date of pistils, harvest date, shell thickness, all nut and kernel measurements and wt. They are above .39 for last shedding of pollen, fruitfulness of laterals, shell seal, number of light colored kernels, kernel veins, and kernel spots, and approx zero for crop and number of good kernels. The precision of these estimates is very high. Thus they should be reliable predictors of rate of genetic gain attainable in such populations when seedlings are selected as parents on the basis of their own performance. The implication of these genetic relationships on the effectiveness and efficiency of breeding methods and selection procedures in walnut are discussed.
Turkey has more than 4 million walnut trees (Juglans regia L.), most of which are derived from seedlings, and are nongrafted trees. This characteristic leads to a huge opportunity to select superior walnut genotypes from natural populations for cultivation and for breeding programs. Several selection studies have been performed in the last decades and few genotypes were selected. The goal of this study was to characterize and determine genetic relationships among 21 walnut genotypes with potential in walnut production using amplified fragment length polymorphism (AFLP) and selective amplification of microsatellite polymorphic loci (SAMPL) techniques. Eight primer combinations (six for AFLP and two for SAMPL) were applied to 21 walnut genotypes and a total of 230 bands of which 50.4% of them were polymorphic were obtained. The SAMPL technique was more effective than AFLP in the separation of very closely related genotypes. Genotypes of the pairs `Maras-18' with `Maras-46', `KSU-5' with `Sutyemez-1', `Maras-12' with `Sutyemez-2,' `Kaman-3' with `Kaman-4', and `KSU-11' with `Maras-10' were the most closely related.