Seasonal changes in carbohydrate and nitrogen contents of olive trees ʻFishomiʼ cultivar in several parts under alternate bearing conditions

Some olive cultivars possess high tendency to alternate bearing, which have a minus economic effect on olive industry. The experiment was performed in an olive orchard located in Shiraz region. Monthly monitoring of concentrations of unstructured carbohydrates (glucose, fructose, sucrose, mannitol and starch), protein, nitrogen, potassium and phosphorus in leaves, branches and roots of olive trees ON and OFF was performed from October 2018 to September 2019. The aim of this study was to evaluate carbohydrate and nutrient reserve changes on flower initiation in ON and OFF olive trees. The results showed that there was a significant difference between carbohydrate concentrations (glucose, fructose, sucrose, mannitol and starch), protein, nitrogen, potassium and phosphorus in the leaves, branches and roots between ON and OFF trees during bearing cycle. During autumn and winter, carbohydrate concentrations showed an upsurge trend in different parts in OFF trees. The content of nitrogen ramped up in the leaves in both ON and OFF trees; whereas, it was declined in the branches as well as roots in both trees during autumn and winter. Furthermore, the content of potassium showed a downward trend in the leaves and branches during autumn and winter. In spring and summer, a better percentage of carbohydrates was recorded in olive organs in OFF trees than in ON trees. In July, the concentration of carbohydrates and amount of nitrogen of OFF trees in all samples was higher than that in ON trees. In July, carbohydrate content and mineral content declined in ON trees. The deficiency of carbohydrate and nutrient reserves during the flowering induction affected vegetative growth strength, fruit size, and flowering in the spring of the subsequent year. Simple correlations were shown for 21 measured traits for ʻFishomiʼ seed olive cultivar in different months, respectively. The correlation coefficient showed that there was the most positive correlation between leaf starch and total leaf carbohydrate. The presence of carbohydrate and nitrogen reserves played a key role in flower induction of olive trees and was expressed as crucial parameters to stimulate alternate bearing.