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Wesley T. Watson*, David N. Appel, Michael A. Arnold, Charles M. Kenerley, and James L. Starr

Phymatotrichopsis omnivora (Duggar) Hennebert (syn. Phymatotrichum omnivorum Duggar) is a recalcitrant soilborne pathogen that causes serious root rot problems on numerous plant species in the southwestern United States and northern Mexico. Apple trees [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. (syn. M. domestica Borkh. non Poir.)] are highly susceptible to P. omnivora with most tree death occurring in the summer months. Studies were conducted from 1996 to 1999 to examine when and at what rate infection and colonization of roots of apple trees by P. omnivora actually occurs. In three-year-old trees growing in orchard soils in 45-gallon containers (171,457 cm3) and inoculated with sclerotia in August 1997, infection occurred in the nursery after 12 weeks. For trees inoculated with sclerotia in February 1998, infection occurred within 15 weeks. After 18 weeks, 100% of trees were infected after inoculation in August and 80% of trees were infected after the February inoculation. This information is vital to understanding the epidemiology of Phymatotrichum root rot in apple orchards.

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David R. Rudell, John K. Fellman, and James P. Mattheis

Repeated preharvest applications of methyl jasmonate (MJ) to 'Fuji' apple [Malus sylvestris var. domestica (Borkh.) Mansf.] fruit were evaluated for impacts on peel color, size, fruit finish, and maturation. MJ treatments at 2 week intervals began 48 days after full bloom (DAFB) (early season) or 119 DAFB (late season) and fruit were harvested 172 DAFB. MJ treatment stimulated significant increases in peel red color following the initial application and thereafter. Early season MJ treatment reduced fruit diameter and length to diameter ratio but slowed softening and starch hydrolysis. Fruit receiving late season MJ treatments had increased incidence of bitter pit and splitting, shorter green life, and slower softening. Results suggest preharvest application of MJ impacts apple color development and other aspects of fruit quality. Chemical name used: methyl 3-oxo-2-(2-pentenyl)cyclopentane-1-acetate (methyl jasmonate).

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Desmond R. Layne, Zhengwang Jiang, and James W. Rushing

Replicated trials were conducted in Summers 1998 and 1999 at two commercial orchards (A and B) to determine the influence of a metalized, high density polyethylene reflective film (SonocoRF) and aminoethoxyvinylglycine (ReTain), on fruit red skin coloration and maturity of `Gala' apples (Malus sylvestris var. domestica). There were four experimental treatments: 1) nontreated control; 2) reflective film (RF); 3) ReTain; and 4) RF + ReTain. RF was applied 4 weeks before anticipated start of harvest by laying a 5-ft-wide (150-cm) strip on each side of the tree row in the row middle. ReTain was applied 4 weeks before harvest at the commercial rate in one orchard and at 60% of the commercial rate in a second test. ReTain delayed fruit maturity. Fruit from RF trees had a significantly greater percent surface red color than fruit from trees not treated with RF. Fruit from RF + ReTain were significantly redder and had higher soluble solids concentration (SSC) than fruit from trees treated with ReTain alone. There were no differences in size, fruit firmness or starch content between fruit from RF and RF + Retain. RF appears to be a method to increase red skin coloration in `Gala' apples treated with ReTain without adversely impacting maturity.

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Kevin R. Kosola, Beth Ann A. Workmaster, James S. Busse, and Jeffrey H. Gilman

roots from apple trees [ Malus sylvestris var. domestica (Borkh.) Mansf.] at the University of Wisconsin Peninsular Agricultural Experiment Station near Sturgeon Bay (lat. 44°52′51.96″ N, long. 87°20′7.8″ E) on 13 May 2004. The soil type was an Emmet

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James D. Hansen

Durations of ultrasound treatments were evaluated for efficacy in removing or destroying external pests of apples (Malus sylvestris var domestica). Egg hatch of codling moth (Cydia pomonella; Lepidoptera: Tortricidae), was inversely related to time of ultrasound exposure, although egg mortality was less than 60% after 45 min of treatment. Mortality of twospotted spider mite (Tetranychus urticae; Acari: Tetranychidae), and western flower thrips (Frankliniella occidentalis; Thysanoptera: Thripidae), was directly related to ultrasound durations; adding detergent to the ultrasound bath increased treatment efficacy. Ultrasound did not remove san jose scale (Quadraspidiotus perniciosus; Homoptera: Diaspididae), from the fruit surface. Ultrasound, which can be incorporated in the packing line, shows promise as a postharvest phytosanitation treatment against external pests.

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David R. Rudell and James P. Mattheis

`Golden Delicious' apple [Malus sylvestris var. domestica (Borkh.)] cortex disks suspended in solutions containing a nitric oxide (•NO) donor [S-nitrosoglutathione (GSNO) or sodium nitroprusside (SNP)], •NO gas, or nitrite (KNO2) were used to identify impacts of •NO on ethylene production and NO2 on •NO and ethylene production. Treatment with GSNO or SNP reduced ethylene biosynthesis compared with control treatments containing equimolar concentrations of oxidized glutathione (GSSG) or Na4(CN)6 respectively. Apple disk exposure to •NO gas did not impact ethylene production. Treatment with NO2 resulted in increased •NO production and decreased ethylene biosynthesis. Generation of •NO increased linearly whereas ethylene generation decreased exponentially with increasing NO2 treatment concentration. •NO was enhanced in autoclaved tissue disks treated with NO2 , suggesting that its production is produced at least in part by nonenzymatic means. Although this evidence shows •NO is readily generated in apple fruit disks by NO2 treatment, and ethylene synthesis is reduced by •NO/NO2 generated in solution, the exact nature of •NO generation from NO2 and ethylene synthesis modulation in apple fruit disks remains to be elucidated.

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Richard P. Marini, John A. Barden, John A. Cline, Ronald L. Perry, and Terence Robinson

The influence of rootstock on average fruit weight was evaluated for a subset of data from a multilocation NC-140 apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] rootstock trial. Data for eight dwarf rootstocks were collected at four locations for 2 years. Analysis of covariance was used to evaluate the effect of rootstock on average fruit weight when crop density or number of fruit per tree was included in the linear model as a covariate. When number of fruit harvested per tree was used as a covariate, average fruit weight was not affected by rootstock in either year in Ontario. In Michigan and Virginia, rootstock and number of fruit per tree, but not the rootstock × number of fruit interaction, were significant, so common slopes models were used to estimate least squares means for average fruit weight. In general, trees on M.27 and P.1 produced the smallest fruit, and trees on B.9, M.9 EMLA, and Mac.39 produced the largest fruit. In New York the interaction of rootstock × number of fruit was significant, so least squares means were estimated at three levels of number of fruit per tree. Both years, at all levels of number of fruit, trees on M.26 EMLA produced the smallest fruit and trees on M.27 EMLA produced the largest fruit. Average fruit weight was most affected by number of fruit per tree when Mark was the rootstock. In general, results were similar when crop density was used as the covariate, except that trees on M.27 EMLA did not produce small fruit in Michigan and Ontario.

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Denise Neilsen, Peter Millard, Gerald H. Neilsen, and Eugene J. Hogue

Uptake, recycling, and partitioning of N in relation to N supply and dry matter partitioning was determined for 3- and 4-year-old `Elstar' apple trees [(Malus sylvestris (L) Mill. var. domestica (Borkh.) Mansf.] on Malling 9 rootstock in 1994 (year 3) and 1995 (year 4), respectively. Trees received N yearly as Ca(NO3)2 at 20 g/tree applied on a daily basis through a drip irrigation system. The fertilizer was labelled with 15N in year 3 to allow quantification of remobilization and uptake. The trees were not allowed to crop in years 1 and 2 and were not thinned in years 3 and 4, thereby establishing a range of crop loads. Dry matter and N contents were measured in fruit, midseason and senescent leaves and prunings collected in year 3, in midseason leaves, and in components of the whole trees, harvested in fall of year 4. Labelled N withdrawn from leaves in year 3 was less than that remobilized into leaves and fruit in year 4, indicating that senescent leaves were not the only source of remobilized N. Nitrogen uptake efficiency (total N uptake/N applied) in year 3 was low (22.3%). Of the N taken up, ≈50% was removed at the end of the growing season in fruit and leaves. In fall of year 4, the trees contained about 20 g N of which 50% was partitioned into leaves and fruit, indicating that the annual N uptake by young dwarf apple trees is low (≈10 g/tree). Data were pooled to compare dry matter and N partitioning into two major sinks: fruit and shoot leaves. Total fruit dry weight increased, and in year 4, fruit size decreased with fruit number, indicating that growth was carbon (C) limited at high crop loads. The number of shoot leaves initiated in both years was unaffected by fruit number, but leaf size decreased as fruit number increased in year 4. In year 3, the amount of both remobilized and root-supplied N in fruit increased with fruit number, but the N content of the shoot leaf canopy was unaffected. In general, N and C partitioning were coupled and leaf N concentrations were high (2.8% to 3.2%), suggesting that the low uptake efficiency of fertilizer N resulted because the availability of N in the root zone greatly exceeded demand.

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Zhiguo Ju and Eric A. Curry

Effects of Lovastatin treatment on ethylene production, α-farnesene biosynthesis, and scald development were studied using `Delicious' and `Granny Smith' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] and `d'Anjou' pears (Pyrus communis L.) stored in air at 0 °C. During 6 months storage, Lovastatin did not affect internal ethylene concentration but reduced α-farnesene production in a concentration dependent manner in both apples and pears. Lovastatin reduced scald at 0.63 mmol·L-1 and inhibited scald completely at 1.25 or 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. In `d'Anjou' pears, Lovastatin at concentrations from 0.25 to 1.25 mmol·L-1 inhibited scald completely. After 8 months storage, inhibition of scald in both apples and pears by Lovastatin was concentration-dependent but none of the concentrations totally eliminated scald. Compared with 11.8 mmol·L-1 diphenylamine, Lovastatin treatment reduced scald to the same level at 1.25 mmol·L-1 in `d'Anjou' pear and 2.50 mmol·L-1 in `Delicious' and `Granny Smith' apples. Lovastatin did not affect apple or pear fruit color, firmness, soluble solids content, or titratable acidity during storage in either apple or pear compared with the controls. Chemical name used: [1S-[1a (R °), 3α, 7β, 8β (2S °, 4S °), 8αβ]]-1,2,3,7,8,8α-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1-naphthaienyl 2-methylbutanoate (Lovastatin).

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Richard P. Marini

Data obtained over two years from chemical thinning experiments with `Redchief Delicious' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Manst.] on Malling 26 (M.26) rootstock were used to estimate mean fruit weight (MFW) and mean fruit value (MFV) using two sampling methods. The estimated values were compared with the true MFW and the true MFV calculated from the entire crop from a tree. Statistical techniques were used to assess agreement between the values obtained with estimation methods and the true values. Estimates of MFW obtained from a 20-fruit sample per tree may differ from the true value by ≈13% and estimates obtained from weighing all fruit on three limbs per tree may range from 11% to 19% of the true mean. Estimates of MFV obtained from packouts of a 20-fruit sample may differ from the true value by about $0.04 (U.S. dollars)/fruit and estimates from packing out all fruit on three limbs per tree may differ from the true mean by about $0.07/fruit. Analysis of variance was performed on each data set. The resulting P values differed for the three methods of calculating MFW and MFV. Therefore, erroneous conclusions may result from experiments where MFW and MFV are estimated from subsamples. Error associated with estimating fruit weight and fruit value from the sampling methods employed in this study may be larger than many pomologists can accept. Until protocols for sampling apple trees, which account for the important sources of within-tree variation, are developed, researchers should consider harvesting the entire crop to calculate MFW and MFV.