Response of Bosc and Cold Snap™ pears to thinning with NAA, 6-BA, ACC, and s-ABA

Abstract

Adjusting the crop load of European pears (Pyrus communis L.) by hand thinning is currently required to ensure marketable size of most cultivars grown in Ontario. The benefits of thinning pears chemically and its effect on fruit quality and fresh-market returns were investigated in a 3-yr study where a series of foliar chemical thinning sprays were applied during the 10-mm fruitlet stage to Bosc and Cold Snap™ pear trees growing in commercial orchards in the Niagara Peninsula, Ontario. Treatments included an untreated and hand-thinned control and two concentrations each of 6-benzyladenine (6-BA; 75 and 150 mg L−1), naphthalene acetic acid (10 and 20 mg L−1), 1-aminocyclopropane carboxylic acid (150 and 300 mg L−1), and s-abscisic acid (s-ABA; 150 and 300 mg L−1). Overall, all thinning products reduced crop load at least once in the 3-yr study, although this varied by year and cultivar. Higher concentrations were more effective than lower concentrations. Naphthalene acetic acid (both rates), 150 mg L−1 of 6-BA, and 300 mg L−1 of s-ABA were the most consistent at thinning the crop. As the crop load of control trees was not heavy, minimal hand thinning was required and all thinning treatments reduced crop value compared with the untreated trees. There were minimal effects on starch hydrolysis, soluble solids, fruit firmness, and skin colour at harvest.

Postbloom Thinning of ‘Bartlett’ Pear with Metamitron

“…The thinning activity of metamitron on apple was associated with reduced Fv/Fm values (McArtney et al, 2012). Indirect photosynthetic inhibition by ABA was also associated with fruitlet abscission of apple (McArtney et al, 2014) and pear (Arrington et al, 2017;Einhorn and Arrington, 2018); however, the consistent thinning of pear by ABA (Arrington et al, 2017;Cline et al, 2018;Greene, 2012) was not similarly demonstrated for apple (McArtney et al, 2014;Greene, 2012).…”

Managing Crop Load in European Pear (Pyrus communis L.)—A Review

“…In cv. 'Forelle', Theron et al [64] found differing responses to ABA application between regions and years, and Cline et al [49] reported inconsistent results over the three years of their study on cvs. 'Cold Snap TM ' and 'Bosc', but did find that 300 mg/L had a greater thinning effect than 150 mg/L.…”

“…Fruit size distribution was shifted in this study by both dose rates, but the effect was greater at the higher application rate of 100 mg/L with more fruit in the larger size categories and reduced numbers in the small size categories. Cline et al [49] reported that in Ontario Canada, 150 mg/L BA at the 10 mm fruitlet stage was more consistent as a thinner of cvs. 'Bosc' and 'Cold Snap TM ' than 100 mg/L, but as crop load was not heavy, crop value was reduced compared with untreated trees due to a reduction in yield.…”

“…'Amanlis', 20 mg/L for 'Keiserinne' and 'Moltke' and 20-30 mg/L for 'Clara Frijs'. In Ontario, Canada, Cline et al [49] reported thinning effects with 10 and 20 mg/L NAA applied at the 10 mm fruitlet stage in several trials on 'Bosc' and 'Cold Snap TM ' over three years, although they did find variation in the thinning response between the years and cultivars studied. Gonkeiwicz et al [50] also observed a 33% reduction in crop load of 'Conference' pear with 20 mg/L NAA applied at the 12 mm fruitlet stage.…”

“…According to Arrington et al [69] fruit firmness, TSS content and titratable acidity were unaffected by ABA treatments, but Green [68] found an increase in flesh firmness and soluble solids. In their three-year study of 'Cold Snap TM , and 'Bosc', Cline et al [49] reported some improvement in fruit size but a decrease in yield and crop value which offset the increase in fruit size.…”