Scion Substitution: A New Strategy to Control Citrus Variegated Chlorosis Disease

Citrus variegated chlorosis (CVC) disease, caused by the xylem-limited and insect-transmitted bacterium Xylella fastidiosa, has caused severe losses in orange production in Brazil. Disease control requires insecticide applications, tree removal, and pruning of symptomatic branches. Pruning success has been erratic, especially in areas of high disease incidence. In this work, in planta X. fastidiosa distribution and the effectiveness of severe pruning procedures for curing diseased adult trees were investigated. Most sampled upper parts of the trees contained X. fastidiosa, but at higher frequencies in symptomatic branches. Removal of all main branches (decapitation) was not effective and revealed a 20 to 30% incidence of latent infections. Trunk decapitation resulted in a higher number of healthy scions but killed 10 to 30% of the remaining trunks. Removal of all scion and grafting the newly sprouted shoots of 'Rangpur' lime (Citrus limonia Osbeck) or 'Cleopatra' (Citrus reshni Hort. ex Tan.) rootstocks with healthy buds allowed production of fast-growing and productive new scions that remained free from CVC for at least 2 years in four locations. With this method, highly affected trees do not need to be fully removed and the costs involved in this practice and in young tree acquisition and plantings are circumvented; therefore, it is a feasible option for less technically inclined small growers in Brazil.