3rd Edition of Agriculture, Forestry, and Horticulture World Conference 2027

Abstract

Flower bud abscission in pistachio (Pistacia vera L.) poses a significant challenge in orchards, closely associated with alternate bearing, and carbohydrate availability. Silicon (Si) is recognized as an important element that supports plant growth and development; however, research on the effects of silicon on carbohydrate levels and abscission reduction in pistachios and other plants is still lacking. Therefore, this study aimed to investigate the role of foliar silicon (Si) as a nutrient in the expression of key carbohydrate metabolism genes and the antioxidant defence system in the abscission zone (AZ). Foliar silicon was applied at concentrations of 0, 5, and 10 g L^-1 at 14 days after full bloom (DAFB) in two commercial pistachio cultivars, including “Fandoghi” and “Akbari,” during the 'ON' year. Biochemical analyses showed that Si, particularly at 10 g L^-1 in ‘Akbari’, significantly enhanced catalase (CAT), peroxidase (POX), and superoxide dismutase (SOD) activities, leading to a reduction in reactive oxygen species (ROS) accumulation in AZ. The highest catalase enzyme activity was observed at 10 g L^-1 silicon in the “Akbari” cultivar (1.3 nmol/min/mg protein), while the highest SOD activity was found in the “Akbari” and “Fandoghi” cultivars with 5 and 10 g L^-1 silicon, respectively. Sucrose was the main soluble sugar in the AZ of the pistachio cultivars studied, with sucrose content 1.72 times higher compared to the control at 5 and 10 g L^-1 of Si. Additionally, glucose content increased in both cultivars, with a significant increase of 2.90 mM at 5 g L^-1 of Si. Molecular assays revealed upregulation of α-/β-amylase, galactinol synthase (GolS), starch synthase, and callose synthase (CalS) genes in the AZ, corresponding to elevated levels of sucrose, glucose, and fructose, especially in Si-treated “Akbari” cultivars. These findings suggest that silicon enhances carbohydrate allocation and antioxidant capacity, providing a dual-mode mechanism to mitigate flower bud abscission and improve yield stability in pistachio cultivation. The simultaneous regulation of these genes and activation of the carbohydrate storage and consumption pathway during the critical flowering stage by silicon indicate its dual role in regulating the expression of carbohydrate pathway genes.