Application of some bloom thinning techniques to overcome alternate bearing in pistachio (Pistaciavera L.)

Abstract

Biennial bearing is a frequent problem in pistachio (Pistaciavera L.) production and gets worse with age. Abscission of floral buds is due to competition between growing seeds on 1-year-old shoots and developing buds on current season growth. To avoid it, thinning could be a common cultural practice in orchard management. Three chemical thinners including gibberellic acid (GA3; 50, 100 and 150 mg/L), naphthalene acetic acid (NAA; 40, 80 and 120 mg/L) and ethephon (75, 150 and 200 mg/L), and hand thinning (20%) were applied in a commercial homogenous orchard of pistachio cv.‘Akbari’ 2 weeks after full bloom during 2017–2018 in Rafsanjan, Iran. Thinning rate and quantitative and qualitative traits were investigated in comparison to the control in the split plot arrangement in a randomized complete block design. Ethephone at 200 mg/L and NAA at 120 mg/L caused the highest fruit abscission. Hand thinning, NAA (120 mg/L) and all ehtephone treatments decreased flower bud abscission by about 30% in the “on” year. Vegetative traits such as shoot length and leaf area showed significant increase under the treatments. Chemical thinning remarkably enhanced total non-structural carbohydrate, especially in “on” year. All of the treatments except GA3 increased tree yield in the “off” year. Qualitative fruit characteristics such as nuts per ounce, blank and split nuts percentage improved. Alternate bearing in pistachio tree was adequately controlled and chemical thinning was more effective than hand thinning.