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.
Wesley T. Watson*, David N. Appel, Michael A. Arnold, Charles M. Kenerley, and James L. Starr
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).
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.
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
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.
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.
Luiz Argenta, Xuetong Fan, and James Mattheis
The efficacy of the ethylene action inhibitor 1-methylcyclopropene (1-MCP) applied in water to slow ripening of `Golden Delicious' [Malus sylvestris var. domestica (Borkh.) Mansf.] apples was evaluated in comparison with 1-MCP applied as a gas in air. The material was applied by dipping fruit in 1-MCP water solutions (0, 0.03, 0.3 or 3 μM) for 4 min, or by exposing fruit to 1-MCP gas (0, 0.01, 0.1 or 1 μL·L-1) in air for 12 h. Fruit were held in air at 20 °C for 25 days after treatment or stored at 0.5 °C in air for up to 6 months followed by 7 days in air at 20 °C. Application of 1-MCP in water or air delayed the increase in respiration and ethylene production associated with fruit ripening, and reduced the amount of fruit softening, loss of acidity and change in peel color. Treatments applied in water required a concentration 700-fold higher compared to those applied in air to induce similar physiological responses. Fruit responses to 1-MCP varied with treatment concentration, and the maximum effects were obtained at concentrations of 0.1 or 1 μL·L-1 in air and 3 μM in water. Peel color change was impacted less than retention of firmness and titratable acidity for some 1-MCP treatments. Treatment with 1-MCP was less effective for slowing peel degreening when treated fruit were stored at 0.5 °C compared to storage at 20 °C. In 1 of the 3 years of this study, fruit treated with 1-MCP and stored in air at 0.5 °C developed a peel disorder typified by a gray-brown discoloration that is unlike other disorders previously reported for this cultivar.
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.
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.
Kate M. Maguire, Nigel H. Banks, Alexander Lang, and Ian L. Gordon
Research quantified contributions to total variation in water vapor permeance from sources such as cultivar and harvest date in `Braeburn', `Pacific Rose', `Granny Smith', and `Cripps Pink' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. In a study on `Braeburn' fruit from eight orchards in Central Otago, New Zealand, >50% of the total variation in permeance was associated with harvest date. This variation was the result of a large increase in water vapor permeance from 16.6 to 30.2 (se = 0.88, df = 192) nmol·s-1·m-2·Pa-1 over the 8 week experimental harvest period. Fruit to fruit differences accounted for 22% of total variation in permeance. Interaction between harvest date and orchard effects explained 7% of the total variation, indicating that fruit from the different orchards responded in differing ways to advancing harvest date. Tree effects accounted for only 1% of the total variation. Weight loss from respiration [at 20 °C and ≈60% relative humidity (RH)] comprised 3.04±0.11% of total weight loss, averaged across all harvest dates. In a second study of fruit of four apple cultivars, almost 30% of the total variation in water vapor permeance was associated with cultivar differences. Mean water vapor permeance for `Braeburn', `Pacific Rose', `Granny Smith', and `Cripps Pink' fruit was 44, 35, 17, and 20 (se = 4.3, df = 300) nmol·s-1·m-2·Pa-1 respectively. Over 20% of the total variation was associated with harvest date and arose from a large increase in water vapor permeance from 21 nmol·s-1·m-2·Pa-1 at first harvest to 46 nmol·s-1·m-2·Pa-1 (se = 5.3, df = 200) at final harvest, 10 weeks later, on average across all four cultivars. There was large fruit to fruit variation in water vapor permeance accounting for 25% of the total variation in permeance values. Tree effects only accounted for 4% of the total variation. Water vapor permeance in `Pacific Rose'` and `Braeburn' increased substantially with later harvest but values remained relatively constant for `Granny Smith' and `Cripps Pink'. A simple mathematical model was developed to predict weight loss from `Braeburn' fruit. Based on these findings, it appears worthwhile to increase the stringency of measures to control weight loss in `Braeburn' and `Pacific Rose'` apples, particularly those harvested late in the season.