Bioregulators can improve fruit size, yield and plant growth of northern highbush blueberry ( Vaccinium corymbosum L.)

Abstract

Abstract The berry size of northern highbush blueberry (Vaccinium Corymbosum L.) is one of the key parameters for determining fruit quality and consumers’ preferences. The aim of the experiment was to apply the bioregulator chemicals that are commonly used and easily accessible in fruit production, primarily for fruit thinning, and look for the positive effects on vegetative growth and fruit quality of highbush blueberry cultivars Duke and Bluecrop. The experiment was conducted in 2016 and 2017 in the commercial highbush blueberry plantation, established in 2014. The following bioregulator treatments were applied at corolla drop: 200 mg L−1GA3 (gibberellic acid), 10 mg L−1NAA (α-naphthaleneacetic acid), 20 mg L−1NAA, 50 mg L−1BA (6-benzyladenine), 100 mg L−1BA and untreated control. During the harvest season, fruit samples were taken at each harvest date and yield per bush was measured. The length and diameter of one-year-old shoots and the leaf area (LA) were measured at the end of the growing season. NAA and BA treatments generally tended to increase the size of blueberry fruits. The most consistent treatments in stimulating the growth of berries were 20 mg L−1 NAA and 100 mg L−1 BA, regardless of the cultivar, harvest date or the year of the study. The increase of fruit weight associated with the increased fruit set contributed to the significant increase in yield per bush in NAA and BA treatments compared to the untreated control in the second experimental year. Both NAA and BA stimulated vegetative growth and the development of LA. On the other hand, GA3 did not affect fruit size, yield nor the development of LA in blueberry, regardless of the cultivar assessed or the experimental year. A single application of NAA at the concentration of 20 mg L−1, or BA 100 mg L−1, at the time of corolla drop, would be a highly recommended practice in the production of northern highbush blueberry.