Defining date palm leaf pruning line in bearing status by tracking physiological markers and expression of senescence-related genes

Abstract

The physiological and molecular markers were evaluated for defining leaf pruning line in bearing status of date palm (Phoenix dactylifera cv. Mazafati). Our results showed that the higher expression of the chlorophyllase (Chlase) gene was concomitant with lower expression of chlorophyll synthase (ChlG) and oxygen-evolving enhancer protein (PSBO) genes in the 6-year-old leaf line. In addition, the 6-year-old leaf line resulted in a lower Hill reaction rate, chlorophyll a/b ratio, photosystem Ⅱ quantum efficiency, and photosynthesis rate. Also, lower expression and activities of catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX) was associated with higher malondialdehyde (MDA) and hydrogen peroxide (H2O2) accumulation in 6-year-old leaf line. These results suggested that the physiological maturity termination, senescence stage initiation, and source to sink transition could occur in 6-year-old leaves. Furthermore, delayed 5-year-old leaf pruning line adjustment in consecutive years could increase quantitative and qualitative yield loss, decrease water use efficiency, and promote alternate bearing and fruit abscission, which is considered a common problem of date growing areas. Further, the senescence-related markers in the alternate bearing trees pruned in pruning line 5 showed a tendency to normal trees. The five-year-old pruning line also resulted in the balance of bunching and loading the alternate bearing trees.