Quantitative variation of phenolic compounds in different tissues of pistachio ( Pistacia vera L. cv. Uzun) associated with alternate bearing

Alternate bearing is a common challenge in horticultural plants, leading to irregular yield in successive years. The potential role of phenolic compounds in regulating this phenomenon, however, is not well understood. This study aimed to investigate the potential role of phenolic compounds in alternate bearing in pistachio trees by analysing samples from different parts of the "Uzun" cultivar over two consecutive years. Seven phenolic compounds (gallic acid, p-coumaric acid, caffeic acid, ferulic acid, chlorogenic acid, catechin, and quercetin) were analysed using high-performance liquid chromatography at 10-day intervals. Significant variations were observed in the levels of certain phenolic compounds between "ON" and "OFF" years, suggesting a potential role for these compounds in alternate bearing. Ferulic acid exhibited a significant decrease in leaves and shoots, indicating its translocation to the nuts, leading to a sharp decline during the nut lignification process. A negative and significant correlation between ferulic and caffeic acid levels was observed in the "ON" and "OFF" years, which may be linked to the alternate bearing and kernel development process in pistachio. These findings provide valuable insights into the role of phenolic compounds in regulating alternate bearing in pistachio trees and could inform future strategies for enhancing pistachio yields and quality.