Optimizing the leaf-to-bunch ratio in ‘Mazafati’ date trees by considering source-sink limitation and physiological-molecular responses

The balance between carbon production and consumption is regulated by source and sink, which can limit plant performance. When there is an imbalance between source and sink, the plant's performance is affected. Thus, source and sink are interdependent. We conducted a two-year study (220–221) to investigate how different leaf-to–bunch ratios (LBR) (7–12) affect source–sink balance and yield in ’Mazafati’ date trees. We also determined the optimal number of bunches per tree as the main carbon sinks competing with other organs. Trehalose is a non-reducing sugar that protects cellular structure and function under stress. We found that 9–10 LBR-trees had no biotic stress due to carbon deficiency or excess, as indicated by minimal expression of the trehalose-6-phosphate synthase (TPS) gene and synthesis of trehalose. This alleviated source-sink limitation and resulted in the highest yield, bunch weight, fruit weight and flavor, water use efficiency, and reduced abscised fruit. Hormones gibberellic acid (GA3) and abscisic acid (ABA), gene expression of sucrose phosphate synthase 1 (SPS1), enzyme activities of sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) related to sucrose synthesis, reducing and non-reducing sugars, and starch increased with increasing LBR in date palm fruit. Based on our findings, we concluded that a LBR of 9–10 optimizes fruit quality in date palm