APS 2009 Annual Meeting Abstract of Presentation

Seed transmission of ‘Candidatus Liberibacter asiaticus’ in citrus without typical huanglongbing
L. BENYON (1), L. Zhou (2), Y. Duan (3), G. McCollum (4), C. Powell (2), D. Hall (4), M. Irey (5), T. Gottwald (4)
(1) USDA ARS, Fort Pierce, FL, USA; (2) University of Florida, IFAS-IRREC, Fort Pierce, FL; (3) USDA ARS, U.S. Horticultural Research Lab, Fort Pierce, FL, USA; (4) USDA –ARS –USHRL, Fort Pierce, FL; (5) United States Sugar Corp., Clewiston, FL
Phytopathology 99:S11

Citrus huanglongbing (HLB) is one of the most devastating diseases of citrus worldwide. In the USA, HLB is associated with ‘Candidatus Liberibacter asiaticus’ (Las) which is transmitted by the insect vector, Asian citrus psyllid (Diaphorina citri), by grafting and by dodder (Cuscuta campestris). However, the seed transmissibility of Las in citrus remains undetermined. We have evaluated seedlings grown from the seeds of typical HLB-affected and atypical HLB-affected citrus trees of sweet orange (Citrus sinensis), Pummelo (C. maxima) and trifoliate (Poncirus trifoliate) during 2007–2009. HLB-like symptoms, such as yellow shoot, blotch mottle and vein corky on the leaves were observed in a low percentage of the seedlings, primarily on trifoliate plants. Using various primer sets that target different genetic loci of the bacterial genome, Las was detected from all three species of citrus, ranging from 2.0% to 41.7% using PCR, nested PCR and quantitative PCR. It is important to note that the Las bacterium detected from the seedlings remains at a very low titer, unlike that in graft- or psyllid-transmitted HLB-affected citrus plants, and most, if not all, of the Las-positive seedlings have not developed typical HLB disease over a three year period. The molecular mechanism of the low-titer, non-lethal but seed-transmissible Las is under investigation.