MONITORING 'CANDIDATUS LIBERIBACTER ASIATICUS' IN A COMMERCIAL ORCHARD OF SWEET ORANGE AND TAHITI LIME IN THE NORTHWEST OF PARANÁ STATE, BRAZIL

Huanglongbing (HLB) is one of the most devastating citrus diseases worldwide, affecting all species of Citrus. Early characteristics of infected trees are individual branches with yellowish leaves, followed eventually by tree decline and death. The objective of this study was to examine seasonal dynamics of within-tree accumulation of ‘Candidatus Liberibacter asiaticus’, the bacterium associated with HLB, in a commercial orchard. Sweet orange and Tahiti lime plants naturally infected with HLB (confirmed by conventional PCR) were monitored for bacterial population using real-time PCR. Total DNA was extracted from the main veins of symptomatic leaves collected monthly over a period of twenty months. The sample from each plant comprised 10 leaves per quadrant, totaling 40 leaves per plant. The 10-leaves sample from each quadrant was analyzed separately. Erratic bacterial accumulation was observed in both sweet orange and Tahiti lime. After detection in one quadrant of the plant, the continued presence of the bacterium in the same quadrant was not verifiable a few months later. In sweet orange trees, the quadrants expressing more severe symptoms had higher bacterial titer, with Ct values between 18 and 33. Similar results were found for Tahiti lime. These results contribute to our knowledge of HLB epidemiology and might help in the search for effective control measures.