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Graft and psyllid transmissions indicate resistance to ‘CandidatusLiberibacter asiaticus’ is expressed in the citrus relative orange jasmine
M. E. HILF (1), D. G. Hall (2). (1) USDA ARS USHRL, Ft Pierce, FL, U.S.A.; (2) USDA ARS USHRL, Fort Pierce, FL, U.S.A.

Huanglongbing (aka citrus greening) is a systemic bacterial disease of citrus associated with infection by the phloem-colonizing bacteria ‘<i>Ca</i>. Liberibacter asiaticus’, (CLas) which is transmitted to non-infected trees by the Asian citrus psyllid (<i>Diaphorina citri, </i>Kuwayama<i>)</i> or by grafting with infected budwood. The rutaceous flowering ornamental plant, <i>Murraya exotica</i> L., commonly called orange jasmine (aka orange jessamine) is a preferred host for <i>D</i>. <i>citri</i> and is a popular landscape ornamental. Experiments were done to evaluate its susceptibility to infection with CLas by psyllid and graft transmission. Transmission experiments with <i>D. citri</i> and <i>M. exotica</i> seedlings conducted in fall 2012 and summer 2013 yielded 1/16 and 5/80 infected seedlings respectively. Grafting experiments done to transmit CLas from citrus to <i>M. exotica</i> showed a significant difference in the survival of budwood which was dependent on the budwood source, with survival of 80% of budwood from non-infected trees and of only 32% of budwood from CLas-infected trees. The psyllid transmission data suggest <i>M. exotica</i> seedling populations are heterozygous for susceptibility to infection and that these results are compatible with a model where resistance is a dominant trait controlled by two genes. The results from grafting experiments suggest this is an active resistance to infection and that resistant <i>M. exotica</i> seedlings can be identified by grafting with budwood from infected citrus trees.

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