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Pinghai Ding*, Minggang Cui and Leslie H. Fuchigami

Reserve nitrogen is an important factor for plant growth and fruiting performance in tree fruit crops. The fall foliar urea application appears to be an efficient method for increasing N reserves. The effect of fall foliar urea application on N reserves and fruiting performance were studied with four year old `Gala'/M26 trees grown in 20 gallon containers in a pot-in-pot system from 2001 to 2003 at the Lewis-Brown Horticulture Farm of Oregon State Univ.. The trees were either sprayed with 0 or 2 times 3% urea after harvest in October. Shoot and spur samples were taken at the dormant season for reserve N analysis. Fruit performance was recorded in the following growing season. The fall foliar application significantly increased spur N reserve and had the trend to increase shoot N reserve but not significantly. The fall foliar application significantly increased tree fruit set and cluster fruit set. With normal fruit thinning, fall foliar urea application has the trend to increase both tree yield and average fruit size; without fruit thinning, fall foliar urea application has the trend to increase tree yield. These results indicate that fall foliar urea application an effective method to increase reserve N for maintaining tree yield.

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Lailiang Cheng, Shufu Dong and Leslie H. Fuchigami

Bench-grafted Fuji/M26 trees were fertigated with seven nitrogen concentrations (0, 2.5, 5.0, 7.5, 10, 15, and 20 mm) by using a modified Hoagland solution from 30 June to 1 Sept. In Mid-October, plants in each N treatment were divided into three groups. One group was destructively sampled to determine background tree N status before foliar urea application. The second group was painted with 3% 15N-urea solution twice at weekly interval on both sides of all leaves while the third group was left as controls. All the fallen leaves from both the 15N-treated and control trees were collected during the leaf senescence process and the trees were harvested after natural leaf fall. Nitrogen fertigation resulted in a wide range of tree N status in the fall. The percentage of whole tree N partitioned into the foliage in the fall increased linearly with increasing leaf N content up to 2.2 g·m–2, reaching a plateau of 50% to 55% with further rise in leaf N. 15N uptake and mobilization per unit leaf area and the percentage of 15N mobilized from leaves decreased with increasing leaf N content. Of the 15N mobilized back to the tree, the percentage of 15N partitioned into the root system decreased with increasing tree N status. Foliar 15N-urea application reduced the mobilization of existing N in the leaves regardless of leaf N status. More 15N was mobilized on a leaf area basis than that from existing N in the leaves with the low N trees showing the largest difference. On a whole-tree basis, the increase in the amount of reserve N caused by foliar urea treatment was similar. We conclude that low N trees are more effective in utilizing N from foliar urea than high N trees in the fall.

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Sanliang Gu, Leslie H. Fuchigami and Victor Sahakian

Applicability of processed fiber (methane digested cow manure) as a substitute for peatmoss for production of various containerized perennial woody plant species with various fertilization and fumigation practices was investigated in this study. Liner plants of five species and rooted cuttings of 41 species were potted in various media containing processed fiber as the replacement of peatmoss with or without fertilization and fumigation, with commercial mix as control. Plants varied in their responses to the media, fertilization, and/or fumigation. Most plant species performed well in the media containing processed fiber. The physical and chemical properties of processed fiber, either alone or mixed with other media components, were satisfactory for producing woody perennial species even with less fertilization and no fumigation.

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Sanliang Gu, Lailiang Cheng and Leslie H. Fuchigami

`Early Girl' tomato plants (Lycopersicon esculentum Mill.) were grown in a medium containing peatmoss and perlite (60%:40% by volume). The medium was drenched with 0% or 5% GLK-8924 antitranspirant. Half of the plants were flushed daily with 250 mL water (leaching), and the other half were subirrigated by capillarity. The solution osmotic potential of the medium was reduced significantly by 5% GLK 8924 treatment, then recovered gradually to the control level after 3 days with leaching or 10 days without leaching. Leaf stomatal conductance, transpiration rate, and plant growth were depressed by the antitranspirant application, and the depression was alleviated by leaching. Neither antitranspirant GLK-8924 treatment nor leaching influenced leaf abscisic acid (ABA) content. The effect of the antitranspirant on leaf gas exchange and plant growth was highly related to the reduction in the solution osmotic potential of the medium, but not to leaf ABA content. Younger leaves had higher stomatal conductance and transpiration rate but lower ABA content than older leaves in general.

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Michael D. Remmick and Leslie H. Fuchigami

Stems of 1-year seedling Washington hawthorn (Crataegus phaenopyrum) and 1-year layers of apple rootstocks M.9 and M.26 EMLA were subjected to positive air pressures in a double-open-end pressure chamber to determine the cavitation response of each taxon. Inferences regarding relative desiccation tolerance of the taxa can be made by comparing the range of applied pressures over which air-seeding and subsequent reduction of water flux through xylem conduits is induced. M.9 rootstock maintained higher levels of water flux relative to M.26 EMLA or Washington hawthorn at pressures between 3.0 to 4.0 MPa, suggesting greater resistance to water stress-induced air-seeding in the former compared to the latter two taxa. The cavitation responses of M.26 EMLA and Washington hawthorn were indistinguishable from each other. Inferences regarding water stress-induced cavitation response will be discussed relative to this technique.

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Michael D. Remmick and Leslie H. Fuchigami

A film-forming antidesiccant (Moisturin-4; Burke's Protective Coatings, Washougal, Wash.), 1:1 (v/v) with water, was applied to dormant, bare-root, 2-year seedlings of Washington hawthorn (Crataegus phaenopyrum), a difficult-to-establish species. Antidesiccant applications were made to nonstressed controls or to stressed plants (13 h air-drying at 19C and 20% RH) either before or after drying. Antidesiccant was applied to stems only (SO), roots and stems (RS), or not at all (stressed controls). Three subgroups of treated plants were measured to assess changes in fresh weight (FW), xylem water potential (XWP), or specific conductivity (k s) of stems before stress, after stress, or 2 to 3 weeks following planting in the greenhouse. Applications of antidesiccant to SO allowed stressed plants to recover prestress levels of FW after 2 to 3 weeks, whereas stressed plants receiving the RS treatment did not fully recover prestress levels of FW. XWP of stressed SO plants tended to increase following outplanting. k s was highly variable, but tended to be higher in nonstressed plants. Nonstressed and SO seedlings had higher percentages of budbreak.

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Jorge H. Siller-Cepeda, Leslie Fuchigami and Tony H. H. Chen

Many seeds of woody plants require low temperature or other treatments to overcome dormancy. Changes in catalase activity and glutathione has been proposed to be associated with the breaking of dormancy. We examined the level of glutathione and catalase activity of cherry seeds (Prunus mahaleb cv. Lambert) exposed to several dormancy breaking agents. Seeds imbibed in water for 24 hrs. were either stratified at 4°C or at 25°C for up to 12 weeks, or exposed to other dormancy breaking agents. Germination test, glutathione and catalase activity were determined weekly and/or after treatment. Analysis of levels and state of glutathione were performed by high pressure liquid chromatography (HPLC), and catalase activity was assayed spectrophotometrically. Total glutathione in dry and imbibed seeds were similar, but, ratio between the reduced and oxidized form were different. Low temperature stratification for 12 weeks increased the reduced form of glutathione six-fold, while percent germination increased up to 94%.

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John M. Englert, Leslie H. Fuchigami and Tony H.H. Chen

Desiccation stress during the postharvest handling of bare-root nursery plants is often responsible for poor performance after transplanting. Alternate methods of handling desiccation sensitive deciduous trees, such as Washington hawthorn (Crataegus phaenopyrum Med.), and herbaceous perennials species, including Iris, Hosta, and Hemerocallis, are needed for improving survival after transplanting.

A new antidesiccant compound called Moisturin has been useful in reducing water loss from Washington hawthorn trees during storage and shipping, and in improving survival and plant performance during establishment. Hawthorn seedlings or multi-stemmed trees treated with Moisturin before a period of water stress had up to 75% less dieback than control or other antidesiccant treatments.

The use of Moisturin treatment and / or protection with plastic bags of topped bare-rooted herbaceous perennials before five weeks of cold storage (2C) was effective in improving the survival of Iris ensata, Iris sibirica, and Hosta plants. Hemerocallis plants survived equally well with all treatments. The greatest effect on reduction of water loss and improvement of survival was when plants were sealed in plastic bags.

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Giovanni Iapichino, Tony H.H. Chen and Leslie H. Fuchigami

An efficient adventitious shoot production protocol has been developed for Rhododendron laetum × aurigeranum. Shoot tips taken from greenhouse-grown plants were cultured on Anderson's medium supplemented with 74 μM 2iP. Axillary shoots were excised and cultured on medium containing 23 μM IAA and 74 μM 2iP. After 6 months, brown callus developed at the cut surfaces of the shoot-tip explants. This callus produced many adventitious shoots (up to 70 per explant). Clusters of adventitious shoots were divided, subculture, and continued to proliferate shoots. An estimated 1600-fold increase in the number of shoots could be readily achieved in 6 months. In vitro rooting of adventitious shoots was accomplished in 4 weeks. Seventy-three percent of shoots rooted on 1/4 strength Anderson's medium supplemented with 28 μm IAA. Plantlet survival was 100%3 weeks after transfer to soil. Chemical names used: 1-H-indole-3-acetic acid (MA); N-(3 -methy1-2-butenyl) -1H-purine-6 amine (2iP).

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Abbas M. Shirazi, Leslie H. Fuchigami and Tony H.H. Chen

Red-osier dogwood sterns, Cornus sericea L., at ten different growth stages were subjected to a series of temperatures ranging from 25C to 60C by immersing them in a water bath for one hour. After heat treatments, the viability of internode tissues were determined by electrical conductivity and ethylene production. Heat tolerance was expressed as LT50, the temperature at which 50% of the tissues were injured. The results suggest that the LT50 of dormant plants remained relatively constant, approximately 53C. During dormancy, heat stress did not stimulate ethylene production from internode tissues. In contrast, tissues from non-dormant plants exposed to heat stress produced increasing levels of ethylene reaching a peak at 40C followed by a steady decrease at higher temperatures. Application of 1-aminocyclopropane-1-carboxylic acid (ACC) to stem segments from dormant plants, following heat treatment, enhanced production of ethylene.