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

Abstract

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.

Socio-Economic Risks Posed by a New Plant Disease in the Mediterranean Basin

“…Besides these vulnerable economic crops, Xf has been detected in several alternative hosts (i.e., ornamental plants, shrubs, and forest trees) under natural conditions, such as Polygala myrtifolia, Nerium oleander, and Prunus avium. Upon infection, Xf is known to cause many different diseases such as Pierce's disease in grapes in California [4], citrus variegated chlorosis in Brazil [25], oak leaf scorch in Florida [26], oleander leaf scorch [27], coffee leaf scorch [28], olive quick decline syndrome in Italy [5]. However, infected plants may also remain asymptomatic without causing any serious damage in the early stage of the infection.…”

An overview of the most threating diseases that affect worldwide citriculture: Main features, diagnose, and current control strategies

“…The CVC disease management is based on vector control through the use of insecticides, the symptomatic plants' elimination, and the affected branches pruning (Gravena et al, 1997;Coletta-Filho et al, 2020;Lopes, 2020). However, branch pruning is not an efficient measure, especially in orchards with a high CVC incidence (Gabriel et al, 2020;Lopes, 2020).…”

“…ex Tan.) with healthy shoots, the new shoots grow with no CVC infection (Lopes, 2020). Based on this method, plants highly affected by this disease do not need to be completely removed, which would reduce the infected plants' eradication costs (Gabriel et al, 2020;Lopes, 2020).…”

Genomic Analysis for Citrus Disease Detection

“…Eradication of infected citrus trees via burning, chipping, or landfill burial is often recommended [48]. Exclusively using pathogen-free budwood for the propagation of nursery stock and grafting newly sprouted shoots with healthy buds is a fundamental component of CVC prevention [48,49]. The X. fastidiosa genome has been sequenced ( [50]; Table 2), presenting technical opportunities for early detection by qPCR and future development of treatments specifically targeting its gene expression.…”