Characterization of shoot flushing maturation of two sweet orange cultivars subjected to different pruning periods and irrigation regimes

Abstract

Currently, huanglongbing (HLB) has severely impacted the citrus industry worldwide due to its rapid spread, reduction in fruit yield and quality, associated with the high cost to manage the disease. Vegetative flushing is the preferred site for feeding and reproduction of the psyllid (Diaphorina citri), the vector of the bacterium Candidatus Liberibacter spp. which is associated with the HLB. As there are no curative methods or genetic resistance to date, the prevention of new infections is essential for the control of this disease. New alternatives for HLB management are being studied in the Thematic Project FAPESP (process 2017/21460-0), in which this proposal is complemented. The main idea of this proposal is to characterize the vegetative flushing maturation of two sweet orange cultivars (´Valencia Americana´ and ´Valencia´) in different management systems (irrigated and rainfed) in the citrus belt of São Paulo, after mechanical pruning in different seasons corresponding to different phenological stages: pre-bloom, petal fall, post-physiological fruit drop, and immature fruit growth. The experimental design will be in randomized blocks with five treatments (pruning periods) and five replications. The flushing maturation will be characterized weekly by assessing color through chlorophyll meter and tissue firmness by penetrometer, using 20 shoot flushing per plot. The maturation time will be estimated for each pruning period by calculating the degree-days within different stages of shoot development. In addition to a better understanding the psyllid´s preference for certain flushing stages, the results of this proposal will effectively contribute to practical information, as it will support citrus growers to monitor the flushing after pruning and program psyllid control actions aimed at reducing primary infections of HLB in orchards.