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Research Updates Related to Apple Quality from the 2008 ASHS Meeting

The following research summaries contain relevant information related to apple quality and postharvest physiology. These were recently presented at the annual meeting of the American Society for Horticultural Science (ASHS) in July 2008. 

Effects of Delayed CA Storage of Apples after Rapid 1-MCP Treatment (C.B. Watkins and J.F. Nock, Cornell University)

Recommendations for maximum acceptable delays after harvest for treatment of apple fruit with 1-MCP (SmartFresh^SM) vary by cultivar and growing region. However, not all storage operations can fill storage rooms within a short period of time. Therefore, the effects of delayed CA storage after treatment of apples with 1-MCP within 2 days of harvest were investigated. ‘McIntosh’ and ‘Empire’ apples were harvested from different regions in New York and treated with 1 ppm of 1-MCP after cooling overnight at 2^oC. Fruit were stored in CA (‘McIntosh’, 2% O₂ + 2% CO₂ and 5% CO₂ after 5 weeks; and ‘Empire’, 2% O₂ + 2% CO₂) after 2, 7 or 14 days.Internal ethylene concentration (IEC) remained low and firmness was maintained in 1-MCP-treated fruit even if CA storage was delayed for 14 days. Variations in responses after 1-MCP treatment were related to fruit maturity at harvest, as indicated by IEC. In a follow-up experiment, ‘Empire’ apples were treated with 1 ppm of 1-MCP after cooling overnight at 2^oC, 8^oC or 12^oC. Fruit were kept at those temperatures for 0, 7 or 14 days before being transferred to 2^oC and CA storage applied. After 10 months of CA storage plus 7 days at 20^oC, apples treated with 1-MCP had no decay, but higher incidences of flesh browning and external CO₂ injury, irrespective of pre-storage treatment. However, the incidence external CO₂ injury increased with increasing delay at warmer temperatures, and was higher at 12^oC than at 8^oC. Overall, the results show that storage of apples in CA can be delayed after treatment with 1-MCP close to harvest, but that slower cooling of fruit may increase the risk of external CO₂ injury.

Flesh Browning Disorder of ‘Cripps Pink’ Apples (H. James and J. Jobling, Hort Research, Australia)

The flesh browning (FB) disorder of ‘Cripps Pink’ (a.k.a. ‘Pink Lady’) apples rapidly became a significant international problem after its initial observation in the year 2000. In this 4-year research study, a combination of pre and postharvest factors were examined over multiple seasons and in several districts to determine their influence on the development of the FB disorder during long-term storage. Following four consecutive seasons of research, the factors responsible for predisposing ‘Cripps Pink’ apples to the FB disorder have been identified and management strategies have been developed. The FB disorder has been classified into three unique disorders based on contrasting mechanisms of physiological damage resulting in the development of FB. Climatic conditions during fruit growth and development were found to predispose apples to developing FB during subsequent long-term storage. ‘Cripps Pink’ apples grown in cool climates were found to develop a chilling injury described as diffuse flesh browning (DFB). DFB was found to be primarily related to the storage temperature; however, it was also influenced by nutrition. Apples grown in warm districts were found to develop the senescent disorder described as radial flesh browning (RFB). RFB was found to be caused by a combination of factors including the storage temperature, composition of the storage atmosphere, fruit maturity at harvest, and tree crop load. The third classification of FB, CO₂ injury, was not found to be associated with climatic conditions during fruit growth and development. The development of CO₂ injury in ‘Cripps Pink’ apples was observed as the formation of lens shaped pits and cavities in the flesh of the fruit when stored in an atmosphere high in CO₂.

Effect of Extenday on Fruit Characteristics and Light Level and Quality of ‘Honeycrisp’ Apples (Crassweller et al., Penn State University)

The influence of the woven plastic reflective cloth ‘Extenday’ (RF), placed beneath ‘Honeycrisp’/M.9 apple trees, was investigated in 2007. The reflective cloth was placed in the herbicide strip on either side of the trees about 2 weeks after full bloom. Experimental plots consisted of three tree units with either the RF or just bare soil (BS) with the middle tree as the data tree in a completely randomized design. There was no difference in percent fruit set between treatments. Fruit density was significantly higher on limbs in the RF treatment. At harvest there was no difference in number of fruit per tree, yield per tree or fruit weight. Tree efficiency and crop load were higher for RF plots. Fruit were harvested on four dates based upon fruit color. The percentage of fruit harvested by treatment on any given date tended to be higher from RF trees harvested on the first three dates. Maturity starch index was significantly higher for fruit from Extenday treatments, with no difference in firmness or soluble solids for fruit harvested on the second harvest. Percent full sunlight (%FS) reflected from BS and RF was determined on three separate dates. On 12 June, reflected %FS at the mid-canopy was greatest for RF treatment. On July 13 at all positions measured in the tree %FS reflected was significantly greater in the RF trees. On 24 July, %FS reflected was significantly greater in the RF trees at 3 out of 4 positions within the canopy. On 19 Sept., spectroradiometer readings indicated that reflected blue light (400-500 nm) from the RF trees was higher than either the BS or from adjacent grass drive row. The Red/Far-Red ratio was also higher in the RF than in the BS or from adjacent grass drive row.

NAA, 1-MCP and AVG Differentially Alter Fruit Abscission and Fruit Ripening in ‘Delicious’ Apples (J. Li and R. Yuan, Virginia Tech.)

Expression of genes for ethylene biosynthesis, ethylene perception, and cell wall degradation in fruit and fruit abscission zones was examined in relation to fruit abscission and fruit softening after spraying with naphthaleneacetic acid (NAA, Fruitone-N), aminoethoxyvinylglycine (AVG, ReTain), 1-methylcyclopropene (1-MCP, Harvista), or the combination of NAA and AVG in ‘Delicious’ apples. The AVG or 1-MCP spray reduced fruit ethylene production and delayed fruit abscission and fruit softening; whereas NAA reduced fruit abscission, but enhanced fruit ethylene production and fruit softening. The combination of NAA and AVG delayed NAA-enhanced fruit softening and resulted in much lower fruit abscission than did either AVG or NAA alone, although there was no significant difference in fruit ethylene production among these treatments. Overall, the data suggests that NAA, AVG, and 1-MCP differentially affect fruit abscission and fruit softening through differentially affecting the expression of different members of certain genes in fruit abscission zones and in ‘Delicious’ apples.

Performance of Air-Induction Nozzles in Medium-Density Apple Orchards (S. McArtney and J.D. Obermiller, North Carolina State University)

A series of experiments was undertaken to compare the performance of an axial fan air blast sprayer equipped with either air induction (AI) or conventional (C) nozzles in medium-density apple orchards. Performance was compared by assessing 1) spray coverage within the canopy at four levels across-row wind speed, 2) ground deposits from airborne drift under still conditions, and 3) biological efficacy of a post-bloom thinning spray. Spray coverage was reduced as across-row wind speed increased, with the most dramatic reduction occurring between 0 to 4 miles per hour (mph) and at heights greater than 8 ft in the canopy. AI nozzles increased spray coverage in the row immediately adjacent to the sprayer compared with C nozzles, regardless of across-row wind speed. AI nozzles resulted in significantly less drift compared with C nozzles under still conditions both in an open field and within a mature ‘Cripps Pink’/M.7 orchard planted in rows 20 ft apart. Sprayer efficiency, measured as the proportion of total spray volume that was intercepted by the tree canopy, was higher with AI nozzles (38%) compared with C nozzles (26%). The efficacy of a post-bloom thinning spray of 6-BA+carbaryl applied to ‘Morgan Spur Red Delicious’/M.111 trees planted at a between-row spacing of 15 ft was slightly greater when applied with AI nozzles compared with C nozzles. Nozzle type, row spacing, and canopy density were major determinants of spray deposition and therefore biological efficacy. AI nozzles should provide equivalent or even improved coverage and biological efficacy compared with C nozzles in well-managed orchards planted at distances of 18 ft or less between rows. However, when orchard rows are spaced greater than 18 ft apart, then AI nozzles will result in reduced spray coverage and chemical efficacy compared with C nozzles because of a reduction in spray carry-over to adjacent rows as a result of reduced airborne drift.

Performance and Economics of High Density Apple Planting Systems for the Processing Market (Robinson et al., Cornell University)

A 5-acre field comparison of 4 orchard systems (Central Leader/M.7 - 385 trees/ha, Vertical Axis/M.7 - 840 trees/ha, Vertical Axis/M.26 - 1196 trees/ha, and Vertical Axis/M. - 1656 trees/ha) with 7 cultivars (NY674, ‘Liberty’, ‘Fortune’, ‘Jonagold’, ‘Mutsu’, ‘Northern Spy’, and ‘Fuji’) was conducted on a commercial farm in Marion, New York from 1994 to 2003. Cumulative yield in the first 5 years and over 10 years was positively related to tree planting density. Yields between cultivars varied widely, with NY674 yielding the most and ‘Northern Spy’ yielding the least. Biennial bearing was high with ‘Northern Spy’, ‘Jonagold’, ‘Mutsu’, and ‘Fuji’, and lower with NY674 and ‘Liberty’. Pruning requirements were highest for the Vertical Axis/M.7 followed by the Vertical Axis/M.9. The first year establishment costs were linearly related to tree planting density. After planting, the low density Central Leader system continued to have a negative cash flow for 8 years, whereas the high density Vertical Axis/M.9 system had a negative cash flow for only 4 years. Thus, the total establishment costs over 6 years were similar across all planting densities. None of the systems had a positive net present value after 20 years, but by 30 years the two highest density systems were positive. Profitability was linearly related to tree density and depended strongly on fruit price, yield, and initial tree price. The optimum planting density appears to be about 1600 trees/ha. This analysis revealed that new processing orchards in New York must have high early yield and mature yields of 60 t/ha and a fruit price of $0.22 per kg to be profitable. For established processing orchards, the minimum profitable yield was 35 t/ha when price was $0.22 per kg.

Water Use, Growth, Nutrients, Yield, and Fruit Quality of ‘Fuji’ and ‘Gala’ Apples (Fallahi et al., Idaho University)

An increasing trend in water shortage and needs for high density orchards mandate the use of more efficient methods of irrigation and rootstocks. In this long-term experiment, effects of seven irrigation systems for ‘Fuji’ and two systems for ‘Pacific Gala’ on four rootstocks on tree growth, water use, fruit quality and mineral nutrients were studied. All forms of drip systems used less water than the full micro-sprinkler. Partial root drying sprinkler used 50% less water than the full micro-sprinkler. Trees with partial root drying drip and deficit drip received 65% of full drip. The amount of water used in July was higher than all other months. When tree were completely mature, each tree with the full micro-sprinkler system used about 6673 L, while full drip used 4118 L per season, which was equivalent to 1010 mm and 624 mm, respectively. Therefore, full drip resulted in as low as 38.3% and as high as 58.3% water savings compared to the sprinkler system. ‘Fuji’ yield and fruit quality, particularly starch degradation pattern (SDP) and size, were affected by irrigation treatments. ‘Fuji’ trees with water deficiency had lower leaf and fruit potassium. ‘Gala’ on B.9 rootstock had more bourse shoots with fruit than those on other rootstocks. ‘Gala’ trees on B.9 ceased terminal growth and formed terminal buds before the trees on other rootstocks. ‘Gala’ fruit from trees on G.30 and B.9 had higher SDP than those on RN-29 and Supporter 4, where trees on RN-29 had higher fruit weight than those on B.9 and Supporter 4. ‘Gala’ on G.30 had more fruit cracks than those on any of the other rootstocks. ‘Gala’ on B.9 had higher leaf nitrogen than those on Supporter 4 and G.30. Trees on B.9 had lower leaf potassium than those on other rootstocks. In contrast, trees on B.9 and RN-29 had higher leaf magnesium, and trees on B.9 had higher leaf calcium, than those on the other rootstocks. Overall, RN-29 and B.9 were found to be suitable for ‘Gala’ in this experiment.

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