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Steven McArtney, John Palmer, Sue Davies and Shona Seymour

The effect of liquid lime sulfur (LS) and fish oil (FO) application during bloom on leaf photosynthesis (Pn) and pollen tube growth in apple (Malus ×domestica) flowers were investigated in order to determine their mode of action as a bloom thinning agent. LS increased the percentage of flowers with fewer than 10 pollen tubes per flower to more than 64% compared to 5% or less in the control. Pollen tubes were completely absent from 27% to 48% of flowers following LS treatment compared with fewer than 4% of flowers having no pollen tubes on control trees. These data indicate that 30% to 50% of flowers that open on the day of LS application are unlikely to set a fruit due to the complete inhibition of embryo fertilization. Increasing the rate of LS from 0.5% to 4% increased the proportion of flowers with limited pollen tube number in a concentration dependent manner. LS suppressed the rate of light saturated Pn; successive LS sprays during the bloom period had an additive effect on suppression of Pn and fruit set. In one study the reduction in Pn was greatest 12 days after application of LS but Pn recovered by about 19 days after initial treatment. In a second study Pn of primary spur leaves had still not recovered when measured 57 days after the first of three applications. FO had no effect on the number of pollen tubes per flower, but reduced Pn and fruit set by about 10% and 20% respectively. An increase in the proportion of flowers with no pollen tubes, and therefore no embryo development, can account, at least in part, for the thinning response following application of LS to apples during bloom. It is likely that suppression of Pn contributes to the thinning response, although the importance of this mechanism will depend on perturbation of the total carbohydrate supply to developing fruit.

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F. Roger Harker, Christopher B. Watkins, Paul L. Brookfield, Mellisa J. Miller, Suzanne Reid, Phillippa J. Jackson, Roderick L. Bieleski and Tim Bartley

Preharvest development and postharvest disappearance of watercore in `Fuji' apples (Malus ×domestica Borkh.) from a northern (Hawke's Bay, latitude 39° south) and southern (Otago, latitude 45° south) region of New Zealand were compared. A new method for quantifying watercore was developed. A photocopy was taken of the symptoms after each fruit was cut in half through the equator, and then the area of affected flesh (photocopies black) was measured using morphometric methods and compared to the area of unaffected flesh (photocopies white). Watercore was more severe and developed earlier in the season in Otago than in Hawke's Bay. In Otago, a block-type watercore predominated, disorder symptoms initially appearing in the tissues located at the junction of two carpels, while in Hawke's Bay a radial-type of watercore predominated, initially appearing in the tissues surrounding the coreline vascular bundles. Regression analysis identified that orchard and harvest date accounted for most of the differences in watercore symptoms and that the initial appearance of low levels of watercore was the best predictor that fruit would start to develop commercially significant levels of watercore. Incorporation of background color, internal ethylene concentration, starch pattern index, and firmness only slightly improved the regression coefficient. Watercore disappeared from the flesh during storage of fruit from both regions. Fruit from early harvests had the least severe symptoms, and the highest rates of watercore disappearance during storage. In fruit with more severe symptoms at harvest, its disappearance during storage was associated with an increase in fruit volume and air space, which occurred despite continuing mass loss. We suggest that during storage, the extracellular fluid associated with watercore symptoms is absorbed into the cells, and thus drives the increase in fruit volume.

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John Cline, Gerry Neilsen, Eugene Hogue, Shawn Kuchta and Denise Neilsen

Use of and interest in organic mulches for both integrated fruit production (IFP) and organic fruit production is increasing given recent efforts to reduce pesticide inputs and improve soil health. A series of four experiments was conducted in the southern interior of British Columbia over 5 years to investigate the use of a spray-on-mulch (SOM) slurry, comprised primarily of recycled waste newsprint fiber, as an effective method to control excessive weed competition and enhance tree establishment and performance. In four experiments, ‘Gala’, ‘Granny Smith’, ‘Ambrosia’, and ‘Honeycrisp’ apple (Malus ×domestica) trees on ‘Malling 9’ (‘M.9’) rootstock were exposed to a series of treatments including a glyphosate check, SOM waste paper, SOM over an organic underlay, SOM incorporated with dichlobenil or tackifier, SOM over black landscape fabric, rowcover cloth, or polyethylene plastic. SOM provided superior weed control in comparison with the glyphosate check treatment, a standard orchard practice in many modern orchards in North America. SOM application over compost, paper, and especially over cloth barriers were found to be more effective weed barriers than SOM alone. In comparison with glyphosate checks, SOM improved tree growth during tree establishment. Although the addition of dichlobenil provided season-long weed control, tree growth was diminished in comparison with SOM alone and remained similar to that of the glyphosate checks. There was little or no benefit of including a 2.5% tacking agent to help improve SOM integrity and long-term surface stability. When applied to bearing 4-year-old trees, SOM provided similar tree vigor as glyphosate checks over four growing seasons. The addition of landscape fabric, plastic, or cloth underlay material in combination with SOM improved tree vigor in formative years, but this benefit diminished over time. SOM-treated trees had greater cumulative yields over glyphosate checks after 3 years of production. SOM provided significant temperature moderation during the summer and winter months and provided moisture conservation during the summer. There were few SOM effects on plant nutrient status.

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Henry W. Hogmire and Stephen S. Miller

As part of a regional NE-183 project (Multidisciplinary Evaluation of New Apple Cultivars), 23 apple (Malus ×domestica Borkh.) cultivars were evaluated for arthropod pest susceptibility. Incidence or injury data were collected from six foliage and eight fruit pests under field conditions over a four year period (2000–03). Cultivars were ranked based on susceptibility (least to most) to each pest, and rankings were summed for members of the foliage and fruit pest group to develop a susceptibility rating for foliage, fruit and all pests combined. Cultivars with lowest susceptibility to foliage pests included `GoldRush' and `Pioneer Mac', whereas `Yataka' and `Cameo' were most susceptible. For fruit pests, susceptibility was lowest for `Pristine' and `Sunrise', and highest for `Cameo', `Fuji Red Sport #2', and `Gala Supreme'. When both foliage and fruit pests were combined, susceptibility was lowest for `Sunrise' and `Pioneer Mac', and highest for `Cameo'. Some increasingly popular cultivars had high levels of injury from a few pests, including plum curculio and apple maggot on `Ginger Gold', codling moth and oriental fruit moth on `Cameo', and japanese beetle, plum curculio and apple maggot on `Honeycrisp'. A positive and significant correlation was found between day of harvest and percent fruit injury from codling moth/oriental fruit moth and tufted apple bud moth/redbanded leafroller, with later maturing cultivars experiencing higher injury levels presumably due to more exposure to later generations of these pests. Differences among cultivars in pest incidence and injury can be used by growers to improve pest management through cultivar selection, or by making modifications in control programs based on cultivar susceptibility.

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John M. DeLong, Robert K. Prange, Peter A. Harrison, R. Andrew Schofield and Jennifer R. DeEll

A final harvest window (FHW), expressed as Streif Index coefficients [firmness/(percentage soluble solids concentration × starch index)], was developed for identifying maximum fruit quality for strains of `McIntosh', `Cortland', and `Jonagold' apples (Malus ×domestica Borkh.) following 8 months of controlled-atmosphere (CA) storage. The Streif Index was calculated during nine preharvest (twice per week) intervals and four weekly harvests over three seasons. The relationship between Streif Index (dependent variable) and day of year (independent variable) of the preharvest and harvest samples was then derived by negative first-order linear regression equations that had parameter estimate (b1) probability values ≤0.0001 for all of the strains. Apples from the four harvest periods were stored in standard CA storage for 8 months and then subjected to a 7-day shelf-life test at 0 °C followed by 5 days at 20 °C. Poststorage quality data were categorized and combined to produce an overall fruit quality rating scale. For each strain, the final harvest (i.e., day of year) was identified as that which directly preceded at least a 10% drop in the poststorage fruit quality rating compared with the first harvest rating. The FHW, expressed as Streif Index coefficients via the regression of Streif Index (Y) on day of year (X), was then calculated as the 3-year final harvest mean with the upper and lower window limits being determined by the standard deviation of the mean. The lower to upper FHW boundaries ranged from 4.18 to 5.34, 4.12 to 5.46, 4.51 to 5.68, 5.23 to 5.99, and 1.38 to 2.34 for Redmax, Marshall and Summerland `McIntosh', Redcort `Cortland' and Wilmuta `Jonagold', respectively. The practical utility of the Streif Index method lies in the ease with which apple fruit maturity at harvest can be evaluated for its suitability for long-term CA storage.

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Douglas Nichols, Charles Embree, John Cline and Hak-Yoon Ju

To determine the effect of blossom and fruitlet thinners on crop load, fruit weight, seed development during the year of treatment, and the subsequent year effect on return bloom, fruit weight and yield, a field trial using the biennial apple cultivar `Northern Spy' (Malus × domestica Borkh.) was established. Treatments applied at full bloom included ATS (ammonium thiosulphate) [12% (w/v) nitrogen, 26% (w/v) S]; TD [15.9% (w/v) diacarboxylic acid, 5.5% (w/v) dimethylalkylamine salt (Endothal)] and SCY [57% (w/v) pelargonic acid (Scythe)]. At 18 days after full bloom (DAFB), oil treatments [98% (w/v) mineral oil (Superior “70” oil)] were applied with S [480 g·L-1 a.i. carbaryl (Sevin XLR)] and without as a means of increasing the efficacy of S. BA [19 g·L-1 a.i. 6-benzyladenine/1.9 g·L-1 a.i. gibberellins 4+7 (Accel)]; S; and/or SA [100% (w/w) 2-hydroxybenzoic acid (salicylic acid)], were also applied in a factorial arrangement on the same day. Fruit abscission was significantly increased the year of treatment with BA, S, BA + S, BA + SA, S + SA, BA + S + SA, oil, and S + oil. Average fruit weight was enhanced by S, BA + S, BA + SA, S + SA, BA + S + SA, and S + oil although in the latter treatment the crop load was very low. Only treatments that included BA reduced the number of fully developed seeds per fruit and seed number per trunk cross-sectional area (TCA) and increased return bloom. Defining the number of fully developed seeds per tree coupled with crop load is proposed as a predictor of return bloom in `Northern Spy'.

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Yong Zhang, Chunxia Fu, Yujing Yan, Yan’an Wang, Ming Li, Meixiang Chen, Jianping Qian, Xinting Yang and Shuhan Cheng

This research was initiated to determine the response of apple (Malus ×domestica) fruit quality to sprays of zinc sulfate (ZnSO4) and sugar alcohol zinc. Two apple cultivars Fuji and Gala were evaluated, the leaf zinc (Zn) concentration of which were about 14.3 mg·kg−1 dry weight without Zn deficiency symptoms. The trees were sprayed with ZnSO4 and sugar alcohol zinc separately during four different developmental stages: 2 weeks before budbreak (P1), 3 weeks after bloom (P2), the termination of spring shoot growth (P3), and 4 weeks before harvest (P4). The fruit was harvested at maturity and analyzed for fruit quality and fruit Zn concentration. Zinc sprays during the four different developmental stages increased Zn concentration of peeled and washed fruit at harvest, without phytotoxicity. The treatments at stages P2 and P4 increased average fruit weight of ‘Gala’ and ‘Fuji’, respectively. The treatments at stages P1 and P4 increased the fruit firmness of ‘Gala’, while the treatments at stages P1 and P2 increased the fruit firmness of ‘Fuji’. The treatments at stages P1, P2, and P4 increased the soluble sugar and vitamin C of ‘Gala’ fruit, while the treatments at all the stages increased the soluble sugar and vitamin C of ‘Fuji’. And the effects of sugar alcohol zinc were equal and more pronounced than those of ZnSO4. Thus, Zn sprays at critical periods can improve fruit quality of apple trees, which show no Zn deficiency symptoms with leaf Zn concentration less than 15 mg·kg−1 dry weight.

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Kentaro Kitahara and Shogo Matsumoto

An S-allele cDNA was cloned from pistils of 'McIntosh' apple (Malus ×domestica Borkh.). The allele, designated Si in Japan and S10 in Europe, is an S-RNase that is very similar (94%) to the S3-RNase at the deduced amino acid sequence level. This allele can be detected by amplification using the polymerase chain reaction (PCR) and specific primers, followed by digestion with restriction enzyme EheI. The S10 allele was discovered in 'Empire', 'Maypole', 'Shinano Red', 'Spencer', and 'Vista Bella'. The S-allele cDNAs sequenced to date are listed with their Japanese and European designations.

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Whitney J. Garton, Mark Mazzola, Nairanjana Dasgupta, Travis R. Alexander and Carol A. Miles

This study was designed to determine the efficacy of canker excision (CE) followed by a subsequent application of cauterization (CAU) and/or fungicide treatment to the excised area for the management of anthracnose canker (caused by Neofabraea malicorticis) on cider apple (Malus ×domestica) trees. Three experiments were conducted from 2015 to 2017, with one experiment each year, in an experimental cider apple orchard in western Washington where trees were naturally infested with N. malicorticis. Treatments were applied once in December and data were collected January through March. Treatments in the 2015 experiment were CE + CAU, CE + CAU + copper hydroxide, CE + 0.5% sodium hypochlorite, Bordeaux mixture (BM) only, and CE + copper hydroxide (control). The 2016 experiment included the same treatments as in 2015 plus one additional treatment, CE + BM. In 2017, one additional treatment was added, CE only, and CAU treatments were removed as they caused significant injury to the trees. Canker size was measured pretreatment, and the treated canker or excised area was measured posttreatment every 2 weeks for 13–15 weeks. Compared with pretreatment, cankers treated with BM did not increase in size, while the excised area treated with CAU increased 28-fold in size on average, and the excised area treated with 0.5% sodium hypochlorite or copper hydroxide increased up to 4-fold in size. Each year new cankers developed in all treatments 13–15 weeks after treatment application, at a time of year when there should not be any spores present to cause new infections. Dark brown streaking, indicative of the disease, was observed in the tissue below the intact or excised cankers 15 months after treatment application all years. Although N. malicorticis was not isolated from symptomatic tissue, symptoms were observed in all treatments including where cankers had not been excised and there was no wounding of the cambium tissue. Findings from this study indicate that of the treatments evaluated, the application of copper hydroxide after CE was the most effective for limiting the number of new cankers, but it did not limit expansion of the excised area. Additional physical and fungicidal strategies need to be tested for effective management of anthracnose canker.

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James M. Wargo, Ian A. Merwin and Christopher B. Watkins

`GoldRush' is a new scab (Venturia inaequalis) resistant apple (Malus ×domestica) with excellent flavor and storage qualities that tends to produce small and russeted fruit. We investigated the effects of rate, timing, and method of nitrogen (N) fertilizers on `GoldRush' fruit size and quality during 1998-99. Fertilizer treatments were 1) no N fertilizer (control); 2) a low N rate of 45 kg·ha-1 (40.1 lb/acre) applied in April (LN-Apr); 3) a low N rate of 45 kg·ha-1 applied half in April and half in June (LN-Apr+Jun); 4) a high N rate of 90 kg·ha-1 (80.3 lb/acre) split in April and June (HN-Apr+Jun); 5) a high N rate of 90 kg·ha-1 applied in April, May, June, and July at 22.5 kg·ha-1 (20 lb/acre) each month (HN-Apr+May+Jun+Jul); and 6) canopy sprays of 1% (wt/wt) urea-N, equivalent to 7 kg·ha-1 (6.2 lb/acre) applied monthly in May, June, July, and August (foliar urea). In 1998, an additional foliar urea spray at 5% (wt/wt) concentration was applied to trees after harvest. The first year's Ntreatments did not affect relative average fruit weights or total yields, but unfertilized trees produced more fruit in smaller size categories. Nitrogen fertilization resulted in greener and softer fruit both years. In the second year, all N additions increased yields compared with controls, but average fruit weight was inversely correlated with crop load. Foliar urea sprays and HN-Apr+May+Jun+Jul treatments increased yields the most. Fruit from LN-fertilized trees were normally distributed across a range of eight box-count size categories, peaking at size 100 both years. In the unfertilized control, fruit size was skewed into smaller size categories and yield was reduced. Total yields were greatest in foliar urea and HN-Apr+May+Jun+Jul treatments, but fruit-size distribution was skewed into smaller categories, peaking at size 138 in the second year. Foliar urea and HN-Apr+May+Jun+Jul treatments produced the highest crop value, but when estimated labor and fertilizer costs were considered, foliar urea and LN-Apr+Jun were the most efficient treatments. Nitrogen fertilizer improved fruit size and market value, but average fruit size in all treatments remained relatively small in both years, indicating that N fertilization alone may not increase fruit size in `GoldRush.'