Multiple season-long sprays of ethephon or NAA combined with calcium chloride on ‘Honeycrisp’ apples: I. Effect on bloom and fruit quality attributes

Abstract

‘Honeycrisp’ apple trees are highly prone to biennial bearing and predisposed to bitter pit. 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 was tested in a 3-yr study. Mature ‘Honeycrisp’ trees were treated with either three or six summer applications of 150 mg L−1 ETH or 5 mg L−1 NAA, all tank-mixed with and without CaCl2, or two or five applications of 150 mg L−1 ACC (without CaCl2). Treatments were applied at 10-d intervals and initiated between 21 and 26 June. All treatments had little effect on enhancing return bloom of ‘Honeycrisp’. NAA, ETH, and CaCl2 all influenced fruit maturity and quality at harvest to varying degrees and across years. Fruit treated with NAA were firmer compared with untreated fruit in 2 out of 3 yr, whereas overall, fruit treated with six sprays of ETH had lower fruit firmness and were more mature. NAA had less influence on fruit quality attributes at harvest than did ETH, and decreased pre-harvest fruit drop (PFD). PFD increased with ETH in 1 out of 2 yr, whereas ACC and NAA both decreased PFD in 1 out of 2 yr. Overall, ETH and NAA, with or without CaCl2, had significant but inconsistent effects on fruit quality and maturity, all dependent on the year and number of applications. Adding CaCl2 decreased fruit firmness in 2 out of 3 yr.

Plant Growth Regulators in Flowering Alternation of the Fuji Suprema Apple Tree

“…Despite many producers in the industry who are using florigenic growth regulators to enhance return bloom, the results of this study indicate that repeat summer sprays of ethephon and naa had little effect on enhancing return bloom of 'fuji suprema' the year following application. These data are consistent with robinson et al [16] and cline [8], who found variable effects of naa or ethephon sprays on return bloom. Naa or ethephon treatments in the 'on' year of a biennial bearing cycle can promote return bloom of apple spurs.…”

“…Applications of naa in 'golden delicious' at weekly intervals during the month preceding the harvest increased the flowering return with the same efficiency as 4 biweekly applications in the period from 60 to 100 days after flowering [12]. Harvey et al [8] report that applications of naa increased the flowering of the apple more than could be explained by the thinning effect, providing direct evidence that naa stimulates the formation of flowers, regardless of production. Ethephon applications also increase flowering return without reducing fruit set [12].…”

“…Alternation research is usually focused on chemical thinning techniques, but in recent decades synthetic bioregulators have proven to be effective in promoting or inhibiting floral induction in apple trees [7]. By applying a flowering promoter such as naphthalene acetic acid (NAA) or Ethephon [8], the bi-annual flowering cycle can be shortened to achieve yields with less variability. Studies aimed at the effect of plant growth regulators in midseason cultivars suggest that the formation of flower buds in cultivars prone to the biennial bearing can be controlled with NAA or Ethephon [9,10].…”

Transcriptomics of Improved Fruit Retention by Hexanal in ‘Honeycrisp’ Reveals Hormonal Crosstalk and Reduced Cell Wall Degradation in the Fruit Abscission Zone

“…The application of ethylene inhibitors such as aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP) reduced the PFD in 'Bisbee Delicious' apples [19]. On the contrary, ethylene releasing compound, ethephon, promoted fruit abscission in 'Golden Delicious' [20] and 'Honeycrisp' [21] apples, indicating that both ethylene biosynthesis and signalling pathways are involved in fruit abscission. Ethylene production and fruit softening increased more rapidly during fruit ripening of PFD-prone cultivar 'Golden Delicious' than non-prone cultivar 'Fuji' [22].…”