Citrus HLB citrus: selection for resistance, survival analysis of scion / rootstock combinations and planting systems

Abstract

The Huanglongbing (HLB) is a highly destructive disease that attacks citrus species. The disease is associated with the bacterium Candidatus Liberibater spp., transmitted by a winged vector, Diaphorina citri, the citrus psyllid. Recent works and observations indicate that rootstocks and management practices can influence the incidence and severity of the disease. This project consists of nine experiments comprising survival analysis to characterize the reaction of Pera and Valencia sweet orange, Ponkan mandarin and Persian acid lime grafted onto 25 rootstocks to HLB under field conditions. In addition, the horticultural performance of these combinations will also be evaluated. The experiments will be carried out in area with high HLB inoculum pressure. The usual vector control will be applied. These rootstocks selections and hybrids have been highlighted in several traits, focusing on high performance and dwarfing characteristics. Other experiments designed to assess the progress of HLB as a function of planting density and orchard planting systems (nursery trees of different sizes, intercropping of citrus plants with rubber tree and interplanting of citrus trees with orange jasmine as a trap plant). Finally, 134 sweet orange and 63 mandarin selections of the BAG (Active Germplasm Bank) of the Citrus Experiment Station of Bebedouro (EECB) and other 643 citrus accessions of the BAG of Embrapa Cassava & Fruits will be challenged against HLB focusing on any resistance or tolerance level at field. The experimental activities will be conducted at the EECB and in commercial orchards. The evaluations include: plant survival analysis, adopting as criteria planting date and the presence of first visual symptoms; incidence and severity of HLB; horticultural evaluation (yield, tree size, fruit quality and drought tolerance); monitoring of the psyllid population on plants; tree phenology (sprouting frequency and shoot density, type and duration of sprouting, flowering precocity); PCR and qPCR molecular analysis on selected combinations for detection and quantification of Candidatus Liberibacter spp. Scion/rootstocks combinations with higher survival rate, the identification of any resistance or tolerance to HLB in citrus accessions and the mitigation of HLB progress following the use of alternative planting systems may turn out to be additional tools in the orchard management currently recommended for HLB control in São Paulo State. (AU)