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Salih Kafkas, Hakan Ozkan and Mehmet Sutyemez

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.

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K.M. Kelley, S.A. Weinbaum, P.B. Catlin and T.T. Muraoka

Nitrogen (N) deficiency reduced biomass and altered N allocation within large walnut tree canopies (Juglans regia L. cv Serr). N-fertilized control trees contained 2.5 times more N in current year spurs, leaves and fruit than did those of N-deficient trees. The N content and biomass allocated to kernels was reduced in N-deficient canopies to a greater extent than was al location to current year shoots and foliage. N removal in abscised leaves and fruit was 3 times greater in canopies of fertilized trees than in N-deficient trees.

A non-destructive method is described to calculate total spur, leaflet and fruit numbers. Calculations were based on ratios of fruit counts on selected scaffold limbs to total fruit number per tree. Dry weight and N content of representative spurs, leaflets and fruit permitted estimation of whole canopy biomass and N content in these organs. N contained in current year spurs and the N lost from the tree in fruit and leaf litter were calculated for both N-fertilized control and N-deficient trees.

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David A. Goldhamer, Robert Beede, Steve Sibbett and Dave Ramos

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.

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Qinglong Zhang and Patrick H. Brown

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.

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William H. Olson and Richard P. Buchner

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.

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Ellen G. Sutter and Hamid Ahmadi

Somatic embryos of Juglans regia transformed with Agrobacterium rhizogenes Rol B gene and non-transgenic lines were proliferated on basal DKW medium. They were then transferred to media containing different concentrations of ABA, IBA and BA to increase the rate of proliferation and maturation. Transgenic embryos required 50 μM ABA and 40 μM IBA whereas non-transgenic embryos required 40μM ABA and 10 μM IBA. Neither kind of embryos required BA. Roots were. induced by drying embryos at 75% for 2-3 weeks until they lost about 30% fresh weight and then transferring them to basal DKW medium for an additional 2 weeks in the dark. Over 50% of the somatic embryos grown on medium containing both ABA and IBA developed well defined root systems compared to less than 15% of embryos grown on basal medium. A combination of 27 μM GA, and 9 μM BA was needed for development of shoot systems and germination of both transgenic and non-transgenic rooted embryos. Anatomical studies followed to characterize the extent of development at each stage.

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Patrick H. Brown

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.

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Kourosh Vahdati, Charles Leslie, Zabihollah Zamani and Gale McGranahan

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).

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V.S. Polito, K. Pinney, R. Buchner and W. Olson

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.

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I. Klein, S.A. Weinbaum, T.M. DeJong and T.T. Muraoka

Localized and carry-over effects of light exposure [as inferred from specific leaf weight (SLW)] on spur viability, flowering, and fruit set were monitored in selected spurs throughout walnut (Juglans regia, cvs. Serr and Hartley) tree canopies. Shaded spurs (i.e., average SLW <4 mg·cm-2) were predisposed to die during the winter, and spur mortality was accentuated among spurs that had borne fruit that season. More catkins and distillate flowers per spur were characteristic of the more exposed positions within the canopy (as indicated by SLW) during the previous summer and following an “off” year. In exposed `Serr' canopy positions (SLW >5 mg·cm-2), catkin and Pistillate flower maturation was reduced in fruiting spurs by 60% and 30%, respectively, in the subsequent year relative to vegetative spurs. In `Hartley', the number of distillate flowers was also reduced by 35% on spurs that fruited the previous year relative to spurs that had been vegetative. Maximum rates of return bloom and fruit set were evident in spurs exhibiting the highest SLW and N per unit leaf area (NA), specific to each cultivar. Among spurs of both cultivars, distillate flower development was more sensitive to shading in the previous season than was catkin development. Shell weight of `Serr' varied positively with SLW, but kernel weight, fruit N, and oil concentration did not vary “with SLW in either cultivar.