Incidence of Candidatus Liberibacter americanus and Ca. L. asiaticus in orange jasmine and citrus trees in urban areas in Sao Paulo State, Brazil

Liberibacters are phloem-limited bacteria associated with huanglongbing (HLB), a destructive citrus disease. Two species occur in Brazil, Candidatus Liberibacter asiaticus (Lam) and Ca. L. americanus (Las), both vectored by Diaphorina citri. Orange jasmine is a widespread ornamental tree and host of both liberibacters and D. citri. We determined liberibacter incidence in cities and villages within the most important Brazilian citrus belt, and their graft-transmissibility. To assess inoculum source potentials, quantitative PCR was applied to all PCR-positive trees. Liberibacter was detected in 91 of 786 trees distributed in 10 of 76 locations, all within the region of high HLB incidence. PCR-positive trees exhibited yellow shoots and/or dieback indistinguishable from those on PCR-negative trees. Among the PCR-positive trees, Lam was proportionally more frequent in the 2005/6 and Las in the 2009 survey. Transmission succeeded only in homologous host combinations, including Lam (2/10) from/to orange jasmine and Lam (5/18) and Las (5/9) from/to citrus. Symptoms were mild and progressed less in orange jasmine probably due to lower liberibacter multiplication. In this host, Lam and Las titers averaged 4.3 and 3.0 log cells/g tissue compared to 5.5 and 7.3 in citrus. Orange jasmine is not as suitable for liberibacter multiplication as citrus. However, its importance to the HLB epidemics should not be underestimated. It is a preferred host of D. citri and is not under any insect- or strict tree eradication-control program.