|Zhou, Lijuan - UNIV. OF FLORIDA|
|Gabriel, Dean - UNIV. OF FLORIDA|
|Weathersbee Iii, Albert|
Submitted to: American Phytopathology Society
Publication Type: Abstract Only
Publication Acceptance Date: March 13, 2008
Publication Date: N/A
Technical Abstract: Citrus huanglongbing (HLB) is one of the most devastating diseases of citrus worldwide. The disease is associated with three different species of Candidatus Liberibacter: Ca. L. asiaticus, Ca. L. americanus and Ca. L. africanus. Ca. L. asiaticus (Las), first detected in Florida in 2005, has been detected from the majority of highly symptomatic HLB samples collected from commercial and residential citrus throughout Florida. The disease in Florida is transmitted by the psyllid, Diaphorina citri. Current diagnosis of HLB relies on symptoms typical of HLB, including yellow shoots (YS) and/or blotchy mottling of leaves (BML), followed by PCR confirmation using Las-specific primers. Here we report a unique disease phenotype, YS without BML in grapefruit, pummelo and sweet orange found in Florida during 2006-2008. In contrast to plants with BML symptoms, the diseased plants expressing YS only contained an apparently very low titer of Las bacterium, which often resulted in failure of detection of the bacterium using current conventional and real-time PCR protocols. We improved sensitivity of HLB detection both by improved sampling and by concentrating the bacterial DNA. The apparent bacterial titers in the diseased plants with YS only and in psyllids collected from these plants appeared hundreds of times lower than those in the diseased plants with BML and in the psyllids from them. Transmission of YS symptoms without BML was demonstrated by grafting. These differences in HLB phenotypes and associated bacterial titer suggest either Las strain variation in Florida or a possible disease complex of HLB pathogens.