Search

‘Honeycrisp’ is a popular apple cultivar, but it is prone to several disorders, especially bitter pit. Previously reported models for predicting bitter pit are biased, indicating that the models are missing one or more important predictor variables. To identify additional variables that may improve bitter pit prediction, a study was undertaken to investigate the influence of canopy position, spur characteristics, and individual fruit characteristics on bitter pit development. ‘Honeycrisp’ trees from two orchards over 2 years provided four combinations of orchards and years. Fruits were sampled from spurs at different canopy positions and with varying bourse shoot lengths and numbers of fruits and leaves. Following cold storage, bitter pit was assessed in three ways: 1) bitter pit severity was recorded as the number of pits per fruit, 2) bitter pit was recorded as a binomial response (yes, no) for each fruit, and 3) the incidence of bitter pit was recorded as the proportion of fruit developing bitter pit. As a result of the high fruit-to-fruit variation, bitter pit severity was associated with canopy position or spur characteristics to a lesser extent than bitter pit incidence. Bitter pit incidence was generally greater for fruits developing on spurs with only one fruit and spurs from the lower canopy. Binomial data were analyzed with a generalized linear mixed model. Fruit harvested from trees with heavy crop loads, and those developing on spurs with multiple fruit and spurs with long bourse shoots had the lowest probability of developing bitter pit. Regardless of how bitter pit was assessed, bitter pit related positively to fruit weight (FW), but the relationship usually depended on other variables such as canopy position, fruit per spur, and leaves per spur. The advantages of fitting binomial data with logistic regression models are discussed.

The goal of this research was to evaluate resistance of apple rootstocks to late winter deacclimation during a 2-day exposure to warm temperatures in Maine. We measured the cold temperature tolerance of xylem, phloem, and cambium from 0 to −40 °C in 1- and 2-year-old shoot pieces from apple rootstock cultivars and advanced selections ‘M.9 T337’ (M.9), ‘M.7 EMLA’ (M.7), ‘Budagovsky 9’ (B.9), ‘Geneva® 41’ (G.41), ‘Geneva 30’ (G.30), ‘Geneva 935’ (G.935), ‘Geneva 814’ (G.814), G.4013, G.5257, and Vineland 6 (V.6) after a 2-day exposure to warm (22 °C) or cold (2 to 4 °C) temperatures. Injury was measured on a 0 to 10 rating scale based on percentage of discolored cross-sectional xylem and phloem, and cambial length and circumference with brown discoloration, with 0 indicating no browning and 10 indicating browning in the entire tissue. Injury was also measured as intensity of browning on a scale of 0 (no browning) to 5 (dark brown to black). The weighted averages of the two ratings were used to calculate an index of browning. Genotypic variation occurred in the degree of deacclimation, which ranged from none to as much as 15 °C loss in hardiness. Two genotypes, ‘G.41’ and ‘M.9’, showed little change in hardiness in both years they were tested. Two genotypes, G.4013 and ‘G.814’, lost substantial hardiness in both years and may be vulnerable to late winter freeze-thaw events, but were among the hardiest before deacclimation. ‘G.935’ and G.5257 showed a small loss of hardiness, whereas ‘B.9’ lost hardiness in the cambium, but not the xylem, and V.6 lost hardiness after warm exposure, but showed almost no injury at temperatures as cold as −35 °C. The loss of hardiness of these four genotypes that were tested in only one year should be verified with additional testing because of the potential for yearly variation.

‘Honeycrisp’ (Malus ×domestica) apples were harvested from a total of 17 mid-Atlantic orchards during 2018 and 2019 to verify a previously published bitter pit prediction model. As in the previous study, bitter pit incidence was associated with low calcium (Ca) levels and high ratios of nitrogen (N), potassium (K), and/or magnesium (Mg) to Ca in the fruit peel and excessive terminal shoot growth. The best two-variable model for predicting bitter pit developed with the 2018–19 data set contained boron (B) and the ratio of Mg to Ca (R2 = 0.83), which is different from previous models developed with data from three individual years (2015–17). When used to predict the bitter pit incidence of the 2018–19 data, our previous best model containing the average shoot length (SL) and the ratio of N to Ca underestimated the incidence of bitter pit. The model is probably biased because one or more important variables related to bitter pit have not yet been identified. However, the model is accurate enough to identify orchards with a low incidence of bitter pit.

Blossom thinning can confer significant benefits to apple growers, including increased fruit size and annual bearing. However, current blossom thinning practices can damage spur leaves and/or fruit. We evaluated the use of short duration forced heated air treatments [thermal shock (TS)] as a blossom thinning strategy for ‘York Imperial’. Using a variable-temperature heat gun, TS treatments were applied to solitary blossoms 24 hours after pollination. Effects of output temperature (five levels) and treatment duration (four levels) were evaluated using a completely randomized design with a factorial treatment structure. Short duration treatments (0.5 and 1.0 seconds) were ineffective for arresting pollen tube growth in vivo. TS temperature required to inhibit stylar pollen tube growth was inconsistent across years. In 2014, TS temperatures ≥56 °C inhibited pollen tubes from reaching the style base at 2.0 and 4.0 second durations. However, in 2015, TS temperatures ≥81 °C at 4.0 seconds prevented pollen tubes from reaching the style base. Inconsistent effects of TS across years were attributed to treatments being applied too late due to optimal conditions for pollen tube growth during the intervening 24-hour period after pollination. Excessive injury to spur leaf tissue was observed at temperatures higher than 84 °C and 70 °C (2.0 and 4.0 seconds, respectively). Pollen tube growth was reduced or arrested at temperature and duration combinations that caused minimal visible injury to spur leaves. Identifying and exploiting structural differences between apple blossoms and vegetative spur leaves may provide insight for the future development of TS or other attempts at developing selective thinning technologies.

‘Brown Snout’ cider apple (Malus ×domestica) is desired by cider makers for its relatively high levels of phenolics, and over-the-row machine harvesting of ‘Brown Snout’ has been demonstrated to provide similar yield to hand harvest at a significantly lower cost. The purpose of this study was to determine if there is a measurable impact of harvest method on the phenolic profile of ‘Brown Snout’ juice and cider to better inform equipment adoption recommendations. Using a redox titration assay, the titratable tannin content (± SE) of juice (0.19% ± 0.01%) and cider (0.19% ± 0.01%) were found not to differ due to harvest method. Using a protein precipitation assay, juice from machine-harvested fruit was found to have lower levels of total tannins [231 ± 36 mg·L−1 catechin equivalents (CE)] than juice from hand-harvested fruit (420 ± 14 mg·L−1 CE). However, the total tannins of cider did not differ due to harvest method, the overall average for machine and hand harvest was 203 ± 22 mg·L−1 CE. The total phenolics of juice and cider did not differ due to harvest method (1415 ± 98 mg·L−1 CE and 1431 ± 73 mg·L−1 CE, respectively). Discriminant analysis based on an average of 33 tentatively identified phenolic compounds, as measured by ultra-high performance liquid chromatography coupled with quadrupole time of flight mass spectrometry, showed no separation due to harvest method in juice or cider. In conclusion, over-the-row machine harvesting of ‘Brown Snout’ resulted in a final product of similar quality at reduced labor costs, and thus shows potential for increasing the commercial sustainability of cider apple operations.

Anthracnose canker, caused by Neofabraea malicorticis, threatens the sustainability of cider apple (Malus ×domestica) production in the maritime climate of western Washington. In the short-term, the disease reduces overall orchard productivity and in the long-term it reduces an orchard’s economic life span. The disease is difficult to manage using cultural practices, and information on fungicide efficacy is limited and contradictory. To address this situation, a 2-year study was conducted to evaluate efficacy of zinc (4.49 lb/acre), basic copper sulfate (2.49 lb/acre), captan (2.94 lb/acre), thiophanate-methyl (0.69 lb/acre), pyraclostrobin plus boscalid (0.38 lb/acre), and combinations of these fungicides to manage anthracnose canker infection in young cider apple trees cultivated in a maritime climate. Trees used in the first year of the study (2016) were found to be infected by anthracnose canker on receipt, so the first year was a measure of disease control and the second year (2017) was a measure of disease prevention. In 2016, when fungicide treatments were applied every 3 weeks from March through October, none of the treatments evaluated inhibited the development of new infections or the expansion of existing cankers (77% increase in canker size on average for all treatments). In 2017, when fungicide treatments were applied every 3 weeks from February through April, two to three new cankers were observed 3 weeks after final treatment application for all treatments. Results from this study demonstrate that the current fungicides recommended for control of anthracnose canker are not reliably effective in the orchard environment of northwest Washington. Future studies should assess the fungicides evaluated in this study applied in rotation with additional systemic fungicides.

The apple (Malus ×domestica) cultivar Santana was shown to have a low allergenicity in a previously reported clinical trial. A protocol was developed to validate these results outside a clinical setting and to market the Santana as a hypoallergenic apple for large-scale consumption. This protocol was designed to ensure safe consumption of the Santana by consumers suffering from apple allergy. We tested the protocol in a pilot in 100 supermarket stores and evaluated in an internet-based survey with 295 respondents. Forty-one percent of the consumers with an apple allergy did not have an allergic reaction to the Santana. Only five percent of the allergic consumers that tried the Santana reported a strong allergic reaction. In concordance with this, the majority (78%) of the mild apple allergic consumers appreciated the Santana. The developed protocol is considered suitable for safe consumption of the Santana providing that information about the possibility of having an allergic reaction among consumers with a mild apple allergy is added to the label.