Citrus Breeding: Genetic Mapping and Localization of QTL for Leprosis

Citrus leprosis, caused by the Citrus leprosis virus -CiLV, is the main viral disease in the Brazilian citrus industry. News reports in countries of Central America and Mexico alert to the dispersion of the disease and increase of its economical importance. Leprosis is typically not systemic disease, and it is characterized by  chlorotic or necrotic, circular and concentric lesions in fruits, branches and leaves, restricted to the feeding place of the vector, the mites of Brevipalpus sp. About 400 citrus hybrids obtained from crosses between Murcott tangor (resistant) and Pera sweet orange (highly susceptible) were evaluated in the field in an endemic region for the disease, with eight replicates of each plant. Incidence and disease severity were assessed using a descriptive scale with different levels of symptoms, where zero corresponded to no symptoms and five to dried branches or plant death. At the end of the evaluations, 279 citrus hybrids were observed as symptomatic and 107 as asymptomatic plants, which has made it possible to obtain phenotypic data for QTL location in an integrated linkage map of the parents previously obtained with DArT molecular markers (Financial support: Fapesp and CNPq).