Elsevier

Scientia Horticulturae

Volume 247, 15 March 2019, Pages 96-100
Scientia Horticulturae

Multiple season-long sprays of ethephon or NAA combined with calcium chloride on Honeycrisp: II. Effect on fruit mineral concentrations and incidence of bitter pit

https://doi.org/10.1016/j.scienta.2018.11.092Get rights and content

Abstract

Honeycrisp apple trees are highly prone to biennial bearing and bitter pit (BP). This 3-y study tested the hypothesis that tank mix sprays of ethephon (ETH), naphthaleneacetic acid (NAA), and 1-aminocyclopropane carboxylic acid (ACC) combined with calcium chloride (CaCl2) can mitigate these production problems. Mature ‘Honeycrisp’ were treated with either three of six applications of 150 mg.L-1 ETH, 5 mg.L-1 NAA or two of five applications of 150 mg.L-1 ACC, all tank-mixed with and without CaCl2 and applied at 10-d intervals starting 21–26 June over three growing seasons. Fruit cortical tissue nutrient concentrations were influenced by applications of CaCl2, ETH, NAA, and ACC. In one year, Ca concentrations were significantly higher in fruit from trees treated with six sprays of ETH or NAA with CaCl2 compared with the untreated control. Compared with untreated trees, fruit Ca concentrations were 115% and 148% higher with three and six applications, respectively. Applications of CaCl2 significantly reduced the incidence and severity of BP post-harvest in two of three years when fruit tissue Ca levels were low. ETH alone also increased the incidence and severity of BP two-fold compared with the control, while early season sprays of NAA reduced BP incidence and severity compared with the untreated control. High and similar levels of BP incidence and severity were observed when six sprays of NAA were applied with or without Ca. Fruit tissue K levels were generally reduced with the addition of CaCl2, and within 1 year, K levels were higher in fruit treated with ACC. Fruit Mg concentrations generally decreased with the addition of Ca or NAA. Six applications of ACC resulted in a 30-fold increase in fruit Mg concentrations compared to the untreated control. Tank mixing CaCl2 with the flower-promoting bio-regulators ETH and NAA proved to effectively reduce BP and increase fruit tissue Ca levels. This approach would offer cost savings when repeat sprays of each are required on a bi-weekly basis.

Introduction

Producers of ‘Honeycrisp’ face several production challenges, including biennial bearing, susceptibility to low fruit calcium (Ca), and storage disorders. Bitter pit (BP), a physiological disorder associated with low fruit Ca, develops on the tree or in storage (Faust and Shear, 1968; Ferguson and Watkins, 1989; Perring, 1986; Vang-Petersen, 1980). The factors associated with this disorder are not fully known, but several factors are well recognized, including low fruit Ca (Turner et al., 1977), cultivar, fruit weight (Perring and Jackson, 1975), harvest date/maturity (Prange et al., 2011), crop load (Robinson and Lopez, 2012; Telias et al., 2006; Volz et al., 1993), seed number, water availability, temperature, and mineral status. The association between mineral nutrition and BP incidence appears to be related to the Ca content of the fruit or its various parts (Himilrick and McDuffie; Ferguson and Watkins, 1989). Cultivar selection, low crop load, large fruit size, intensive pruning, and excessive potassium (K) and magnesium (Mg) fertilization can increase a plant’s propensity to BP (Himelrick and McDuffie, 1983; Faust, 1989).

BP results in significant annual losses wherever ‘Honeycrisp’ is grown. This cultivar, developed by the University of Minnesota and released in 1991 (Luby and Bedford, 1992), is the third most widely planted cultivar by area in Ontario and is being planted at the highest rate of all cultivars in the region (OAG, 2017). ‘Honeycrisp’ is particularly susceptible to BP, in part due to its inherent large fruit size, but also due to genetic reasons not yet fully understood. What is known is that Honeycrisp BP incidence and severity vary by tree age (Bedford, 2001), orchard, rootstock (Kim and Ko, 2004), and crop load (Greene and Weis, 2001). Further, delayed cooling and warmer post-harvest storage conditions favour BP development (DeEll et al., 2016; Li et al., 2012; Mattheis et al., 2017; Watkins et al., 2004). Recent models aiming to predict BP incidence in ‘Honeycrisp’ determined that 65% of the variation was explained by the current season’s extension shoot length and the nitrogen-to-Ca ratio in fruit peel tissue (Baugher et al., 2017).

Ca is mobile in the xylem and moves via the transpiration stream with little movement into the fruit. Consequently, Ca accumulates more in leaves than fruit (Cline et al., 1991; Himelrick and McDuffie, 1983) and apple growers must apply foliar Ca on multiple occasions throughout the growing season. Foliar sprays of Ca remain the gold standard for reducing BP, provided that sufficient elemental Ca is applied to fruit during the fruit growth and development period to raise fruit Ca levels above 4–5 mg/100 g (fresh wt.) (Perring and Jackson, 1975; Turner et al., 1977). Efficacy is based on sufficient elemental Ca being absorbed by the fruit, not the formulation of Ca (Bramlage et al., 1985). Calcium chloride (CaCl2) remains the most effective and cheapest form of Ca available to growers (Biggs and Peck, 2015; Crassweller, 2016; Peryea et al., 2007). In Ontario, a minimum of 12 kg ha−1 per season of elemental Ca applied over a minimum of four foliar sprays are recommended to avoid BP on susceptible cultivars such as ‘Northern Spy,’ ‘Red Delicious,’ and ‘Honeycrisp’ (OMAFRA, 2016). Rosenberger et al. (2004) advise a much lower rate: 3.4 kg ha−1 of elemental Ca per season applied over six dilute sprays. This recommendation followed a study in which reductions in BP incidence of up to 90% were obtained with foliar applications of at least 3.25 kg ha−1 (CaCl2) elemental Ca per season (Rosenberger et al., 2014). In Pennsylvania, a range of minimum of 4.5–16 kg ha−1 per season of elemental Ca over 6–8 sprays is recommended to reduce BP (Crasweller, 2016). For the mid-Atlantic USA, rates up to 26 kg ha−1 of elemental Ca per season are recommended to significantly reduce BP incidence in ‘Honeycrisp’ (Biggs and Peck, 2015).

The present study was conducted in light of the global importance of BP in ‘Honeycrisp,’ as well as the issues of high BP incidence and biennial bearing associated with this cultivar. The 3-year study aimed to determine the response of ‘Honeycrisp’ to multiple season-long foliar applications of Ca for mitigation of BP tanked-mixed with ethephon (ETH) and naphthaleneacetic acid (NAA) to enhance return bloom. The potential cost savings in tank mixing these sprays, which are typically applied on a bi-weekly basis, are believed to be considerable. This study specifically tested the hypothesis that CaCl2 tank-mixed with ETH or NAA would be efficacious for improving fruit levels of Ca and reducing BP symptoms.

Section snippets

Materials and methods

An experiment was repeated over three growing seasons to investigate the response of ‘Honeycrisp’ apple trees to tank-mixed foliar sprays of CaCl2 for BP control as well as NAA and ETH to enhance return bloom. Experimental details and treatments have been reported previously (Cline, 2018a, Part 1 of this series). Briefly, ‘Honeycrisp’/M.9 T337 (1.8 x 4.5 m), planted in 2000 and trained to a vertical axe, were used for this experiment. In 2009 and 2013, the following foliar treatments were

Results and discussion

Fruit cortical tissue nutrient concentrations were influenced by applications of ETH, NAA, ACC, and Ca (Table 1, Table 2). In 2013, Ca concentrations were significantly higher in fruit from trees treated with six sprays of ETH with CaCl2 (56% increase) or six sprays of NAA (39% increase) with CaCl2 compared to the untreated control. The contrasts also indicated an overall increase in fruit Ca concentration when CaCl2 was tank-mixed with the ETH and NAA sprays, and when the number of

Acknowledgements

Assistance with data collection and analyses by D. Norton and C. Bakker is gratefully acknowledged.

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