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Sung H. Guak, Lailiang Cheng, and L.H. Fuchigami

Potted apple trees (Malus domestica L. `Gala') were drenched with either water or an antitranspirant (N-2001). After treatment, no additional water was applied to the plants. Abscisic acid (ABA) content of immature and mature leaves was determined by radioimmunoassay after 0, 1, 3, and 5 h and 1, 2, 4, 7, 8, and 9 days after treatment. ABA content of mature and immature leaves of antitranspirant-treated plants peaked 1 and 4 days after treatment, respectively, and remained constant thereafter. In contrast, with increasing water stress, the ABA content of mature and immature leaves of control plants without antitranspirant peaked at 7 and 8 days, respectively. The overall level of ABA in mature leaves of both treatment groups was significantly greater than in immature leaves. The water saturation deficit increased, water and turgor potentials of leaves decreased, and stomatal conductance decreased in response to antitranspirant application. The changes in water relations parameters and stomatal conductance were highly correlated with changes in leaf ABA content.

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Sung H. Guak, Charles C. Shin, and L. H. Fuchigami

Antitranspirant N-2001 (10%), Great Lakes Chemical Corporation, was applied as a soil drench to `Fuji'/EMLA7' apple plants growing in 15 cm pots in a 25/22±3°C (D/N) greenhouse. After bringing pots to field capacity, chemical application was made and water was withheld thereafter. One hour after chemical application, stomatal conductance of treated and control plants was 0.25 and 0.70 cm/sec, respectively. Stomatal conductance of treated plants was maintained at approximately 0.25 cm/sec throughout the test period (28 days). Stomatal conductance of the control plants decreased to 0.25 cm/sec 13 days after treatment due to desiccation. The stem xylem water potential of the treated and control plants was -2.0 and -5.5 MPa, respectively, 28 days after treatment. The relative water content of leaves of treated plants was 45% greater than controls. The average loss of water via transpiration of treated plants was 32% less than the control plants.

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Sanliang Gu, Leslie H. Fuchigami, Sung H. Guak, and Charles Shin

Seedling plugs of `Better Boy' tomato plants (Lycopersicon esculentum Mill.) were potted in 60% processed fiber: 40% perlite (by volume) media amended or nonamended with either crystalline or powdered hydrophilic polymer (2.4 kg·m-3), and treated with one of several concentrations (0%, 2.5%, 5%, 7.5%, and 10%) of antitranspirant GLK-8924, at the four true-leaf stage. Plants were either well-irrigated or subjected to short-term water stress, withholding water for 3 days, after antitranspirant GLK-8924 application. Leaf stomatal conductance, transpiration rate, whole-plant transpirational water loss, and growth were depressed by short-term water stress and antitranspirant GLK-8924. In contrast, hydrophilic polymer amendment increased plant growth, resulting in higher transpirational water loss. The depression of stomatal conductance and transpiration rate by short-term water stress was reversed completely in 2 days after rewatering while the reduction of plant growth rate diminished immediately. The effects of antitranspirant GLK-8924 were nearly proportional to its concentration and lasted 8 days on stomatal conductance and transpiration rate, 4 days on plant growth rate, and throughout the experimental period on plant height and transpirational water loss. Plant growth was reduced by antitranspirant GLK-8924 possibly by closing leaf stomata. In contrast, hydrophilic polymer amendment resulted in larger plants by factors other than influences attributed to stomatal status. Hydrophilic polymer amendment did not interact with antitranspirant GLK-8924 on all variables measured. The application of antitranspirant GLK-8924 was demonstrated to be useful for regulating plant water status, plant growth, and protecting plants from short-term water stress.

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Gerry H. Neilsen, Denise Neilsen, Sung-hee Guak, and Tom Forge

Mature, fruiting ‘Ambrosia’/‘M.9’ apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees were subjected over three growing seasons to a split-plot experimental design involving four irrigation main plot treatments and three subplot crop load treatments with six replicates. This semiarid production region is traditionally irrigated 01 May to 01 Oct. during which time an average of ≈ 15 cm of precipitation occurs. Irrigation treatments were applied through 2 × 4 L⋅h−1 emitters per tree and included I1: daily application of 100% evapotranspiration (ET); or I2: 50% daily ET; or I3: 50% ET applied to one side; and I4: 50%, 25%, or 18% ET-application, applied every second day, 2007–09, respectively. Crop load treatments were imposed annually ≈4 to 5 weeks after full bloom to create low (2.5, 3, and 3.75 fruits/cm2 trunk cross-sectional area (TCSA), medium (4.5, 6, and 7.5 fruits/cm2 TCSA), and high crop loads (9, 12, and 15 fruits/cm2 TCSA), 2007–09, respectively. Leaf and fruit nutrient concentration was affected more by crop load than by any deficit irrigation strategy. Increased crop load increased concentrations of leaf nitrogen (N), calcium (Ca), and fruit Ca in 2 of 3 years and consistently decreased concentrations of leaf and fruit phosphorus (P) and potassium (K) and, in 2 of 3 years, fruit boron (B). Reductions in seasonal water applications (as with I4) reduced leaf P in 2 of 3 years. But, when significant, (usually only 1 of 3 year) increased fruit Ca, magnesium (Mg), P, K, and B concentrations. Crop load also had a dominant effect on fruit nutrient removal rates expressed as kilograms per hectare. High crop load increased removal of all measured nutrients in most years. In contrast, imposition of deficit irrigation strategies often (2 of 3 years) reduced fruit P, Mg, and B removal rates but had little effect on N, Ca, and K. Cumulative evidence suggests that deficit irrigation applied to N, P, K, and B fertigated high density ‘Ambrosia’ apple orchards in combination with crop load reduction to maintain fruit size should usually not create additional nutrient problems. However, low fruit Ca concentrations may occur if the crop is very low. Fertigation of 20 g K/tree/year was insufficient for older trees because inadequate K occurred in all treatments by the third year.

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Sanliang Gu, Leslie H. Fuchigami, Lailiang Cheng, Sung H. Guak, and Charles C.H. Shin

Seedling plugs of `Early Girl' tomato plants (Lycopersicon esculentum Mill.) were potted in peatmoss and perlite (60:40% by volume) medium, fertilized with 8, 16, 24, or 32 g NutriCote Total controlled-release fertilizer (type 100, 13N–5.67P–10.79K plus micronutrients) per pot (2.81 l), and treated with 0%, 2.5%, 5%, or 7.5% antitranspirant GLK-8924 solution, at the four true-leaf stage. Plants were tipped at the second inflorescence and laterals were removed upon emergence. Leaf stomatal conductance, transpiration rate, and growth were depressed by GLK-8924. In contrast, higher fertilization rate increased plant growth but leaf stomatal conductance and transpiration rate were not affected until 3 weeks after GLK-8924 treatment. With 24 g NutriCote per pot, lamina N concentration in GLK-8924 treated plants was 12.5-fold of that in untreated plants, regardless of GLK-8924 concentration. Lamina P, K, Fe, and Cu were greater while S, Ca, Mg, Mn, B, and Zn were not affected by GLK-8924. The reduced growth by GLK-8924 may be due to the reduced stomatal conductance while the increased growth by high fertilization may be due to influences on plant nutritional status.