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G.H. Neilsen, D. Neilsen, L.C. Herbert and E.J. Hogue

A split-plot experimental design was imposed in the year of planting and maintained for the first five growing seasons in a high density apple orchard on M.9 rootstock planted at 1.5 m (within row) × 4 m (between row) in a loamy sand soil susceptible to K deficiency when drip-irrigated. Four N-K fertigation treatments involving low (N1) and high (N2) rates of N combined with 0 (K0) or 15 g K/tree per year (K1) were applied in five replicated and randomized main plot units. Subplots consisted of three-tree plots of each of the apple cultivars Gala, Fuji, Fiesta and Spartan. Soil solution monitoring indicated the maintenance of distinctly different soil solution N and K concentrations in the respective N-K treatments during the study. The most important plant response was prevention of the development of K deficiency by the K1-fertigation treatment. Fertigation of 15 g K/tree generally increased leaf K, fruit K and Mg concentrations, fruit size and yield and fruit titratable acidity and red coloration at harvest for all cultivars. K fertigation also decreased leaf Mg and B concentrations, fruit N, P and Ca concentration and fruit firmness. In addition to leaf K concentrations <1%, K deficiency was associated with fruit K concentrations <100 mg/100 g fresh weight and soil solution K concentration <5 mg·L-1. Increasing the rate of fertigated N when growth was constrained by K deficiency increased leaf N and Mn and decreased leaf P and B, but had no effect on tree vigor or fruit production and quality.

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Xuetong Fan, James P. Mattheis and John K. Fellman

The effect of exogenous methyl jasmonate (MJ) and jasmonic acid (JA) compared with the effect of ethephon on surface color and quality of `Golden Delicious' and `Fuji' apples (Malus ×domestica Borkh.) was studied. Treatments were applied by dipping fruit in water solutions of JA, MJ, or ethephon or by exposing fruit to MJ vapors. Response to MJ vapor treatment depended on fruit developmental stage, with the maximum effect occurring as fruit began to produce ethylene. MJ promoted color changes more effectively than JA. The promotive effect of JA increased with JA concentration. A minimum concentration of 0.1 mmol·L-1 JA was needed to promote significant color change within 15 d at 20 °C. JA at 1 or 10 mmol·L-1 promoted color change more effectively than 0.35 or 3.5 mmol·L-1 ethephon. The magnitude of JA-promoted responses decreased at lower temperatures. Treatments with 10 mmol·L-1 JA or 3.5 mmol·L-1 ethephon were phytotoxic. Treatments using JA at 1 or 10 mmol·L-1 in water promoted loss of fruit titratable acidity compared to controls. Firmness and soluble solids content were relatively unresponsive to JA treatments. Based on these results, using JA and MJ to promote degreening of apple fruit with minimal loss of other quality attributes appears feasible.

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Chad E. Finn, Bernadine C. Strik, Brian M. Yorgey, Theodore A. Mackey, James F. Hancock, Jungmin Lee and Robert R. Martin

planted in 2006 and evaluated from 2008 to 2012 at Oregon State University’s North Willamette Research and Extension Center (Aurora, OR). Fruit titratable acidity, percent soluble solids, and pH were determined at each harvest date in each year from fresh

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Horacio E. Alvarado-Raya, Rebecca L. Darnell and Jeffrey G. Williamson

.05). There was no effect of girdling on fruit titratable acidity (≈2.4%), the ratio of soluble solids:titratable acidity (≈5.0), or pH (≈3.6). 2004 experiment. No data were taken for the beginning of flowering in the 2004 experiment. However

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Xinhua Yin, Jinhe Bai and Clark F. Seavert

Manufacturing, Two Rivers, WI) at about 2500 to 3000 g n for 1 min, and was used to determine sugar and titratable acidity concentrations. Fruit sugar content (%) was determined using a digital refractometer (PR101α; Atago, Tokyo). Fruit titratable acidity was

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Kelly T. Morgan, T. Adair Wheaton, William S. Castle and Laurence R. Parsons

soluble solids (TSS) concentrations in all 3 years ( Table 2 ). However, no significant effect of N rate or irrigation rate on fruit titratable acidity was found. Canopy size and yield of young trees generally increased as irrigation rate increased