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  • Author or Editor: D. W. Greene x
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Plant response to foliar application of plant growth regulators (PGRs) is often variable, in part due to environmental factors. Weather prior to application is thought to influence cuticle development and thus PGR uptake. For example, in growth chamber studies foliar uptake of 1-naphthaleneacetic acid (NAA) is sometimes increased when fruit trees are placed in low temperature and high humidity several weeks prior to application. Environmental conditions over an extended period of time after application may influence PGR conversion to active form (e.g., ethephon), PGR metabolism, or metabolic factors that affect PGR activity in the plant. The effects of environmental conditions on PGR uptake have been investigated extensively in laboratory studies. In many cases, uptake is clearly increased by high temperatures immediately after application. Laboratory studies report a linear positive correlation between temperature and uptake and greater temperature response above 25 °C (77.0 °F). High humidity and longer drying time often are also reported to increase PGR uptake in laboratory studies. These results are consistent with many grower observations on effects of weather on chemical thinning and have been incorporated into many product labels and extension recommendations. However, relatively few field experiments have been reported in which the relationship between PGR response and environmental conditions were assessed. Wash-off studies have demonstrated that rain shortly after application may reduce efficacy of NAA. Several studies demonstrate environmental interaction with metabolic activity involved in PGR action. For example, shading after thinner application is reported to increase fruitlet abscission and enhance effectiveness of some thinning agents. Chemical thinning of apples (Malus ×domestica) with ethephon is reported to correlate strongly with temperature in the days after application, while studies suggest that higher temperatures after aminoethoxyvinylglycine (AVG) application may reduce control of preharvest drop. However, the stage of fruitlet development at apple thinning often appears to be more important than environmental conditions at the time of PGR application. In addition, field experiments indicate that longer drying times at lower temperatures seem to largely compensate for greater uptake rates at higher temperatures. This paper discusses data from published and previously unpublished experiments in order to understand the effects of environment on PGR response variability.

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Cultivar and planting site are two factors that often receive minimal attention, but can have a significant impact on the quality of apple (Malus ×domestica) produced. A regional project, NE-183 The Multidisciplinary Evaluation of New Apple Cultivars, was initiated in 1995 to systematically evaluate 20 newer apple cultivars on Malling.9 (M.9) rootstock across 19 sites in North America. This paper describes the effect of cultivar and site on fruit quality and sensory attributes at a number of the planting sites for the 1998 through 2000 growing seasons. Fruit quality attributes measured included fruit weight, length: diameter ratio, soluble solids concentration (SSC), titratable acidity (TA), flesh firmness, red overcolor, and russet. Fruit sensory characteristics rated included crispness, sweetness, and juiciness, based on a unipolar intensity scale (where 1 = least and 5 = most), and acidity, flavor, attractiveness, and desirability based on a bipolar hedonic scale (where 1 = dislike and 5 = like extremely). All fruit quality and sensory variables measured were affected by cultivar. The two-way interaction of cultivar and planting site was significant for all response variables except SSC, TA, russet, crispness, and sweetness ratings. The SSC: TA ratio was strongly correlated with sweetness and acidity sensory rating, but was weakly correlated with flavor rating. The results demonstrate that no one cultivar is ideally suited for all planting sites and no planting site is ideal for maximizing the quality of all apple cultivars.

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