Physiological aspects of date palm loading and alternate bearing under regulated deficit irrigation compared to cutting back of bunch

Abstract

The study of alternate bearing based on the seasonal changes pattern of tree carbohydrate is the unreviewed issue in the loading physiology of date (Phoenix dactylifera L.) trees. On the other hand, bunch cutting back is a crop improvement practice used in the date orchards, and it is effective on flower induction and fruit set that regulates the quality and growth of fruit in the On year and the amount and yield of the produce in the Off year. Research on an alternative thinning agent with the bunch cutting back is essential for dates in order to be economical and applicable in harsh climates. For this purpose, the experiment was conducted as a combined analysis across years based on randomized complete blocks on ‘Mazafati’ dates of 10–12 years old with different loading in 2017 (Off2017, Normal2017 and On2017), as well as the On condition trees in 2017 plus bunch cutting back (On2017+Cutting back) or regulated deficit irrigation (On2017+RDI). The main objectives of this study were to investigate the fragmentation of carbohydrate reserves of the tree in the annual rotation cycle in different loading, to evaluate the relationship of sugar reserves with production and abscission of flowers and fruits, to determine the effect of the RDI application in the On year on the pattern of sugar changes, hydrolytic enzymes activity, alternate bearing, quantity and quality of the product, and the possibility of replacing it with cutting back. The results confirmed the significant effect of loading rate on the seasonal fragmentation and fluctuation of carbohydrates and the hydrolytic enzymes activity. The results also showed that the RDI treatment, due to the decrease of bunch length, reduced the biennial bearing index (BBI) and improved the qualitative and quantitative traits of fruit better than the cutting back. According to the results of this study, the irrigation condition of trees has the potential to change the marketability and abscission of date fruits and this is a pioneer study of the RDI role as a thinning potential and moderating of date alternate bearing. However, further research is needed to justify the time and duration of this treatment application.