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Prevalence of ‘Candidatus Liberibacter asiaticus’ in citrus and the Asian citrus psyllid in Texas over a 10-year period (2007-2016)

Olufemi Alabi: Dept. of Plant Pathology & Microbiology, Texas A&M University

<div><em>Candidatus </em>Liberibacter asiaticus (CLas), vectored by the Asian citrus psyllid (ACP), is consistently associated with huanglongbing (HLB) in US citrus-producing states. Surveys were conducted in Texas over a ten-year period (2007-2016) to assess the prevalence and titer of CLas in ACP and citrus trees. ACP cohorts and leaf tissues from suspect trees were sampled in residential areas and groves and tested for CLas by qPCR using standard assays. CLas detection in ACP (2011) preceded that of plant tissue (2012) by 10 months. Annual percentages of CLas-positive ACP and leaf tissue over the detection period followed an exponential growth pattern, varying from 0.03% to 13.7% and from 1.2% to 17.4%, respectively. The proportion of HLB detection sites dramatically increased with time reaching 20% of all commercial blocks and 30% of all residential trees surveyed by 2016. Seasonal variations were observed in the percentages of CLas-positive ACP and trees within a year. Significantly more CLas-infected ACP and trees were recorded during fall and winter relative to the hottest summer months under Texas growing conditions. Although mean Ct values of CLas-positive ACP did not vary with time, there was a significant trend of higher bacterial titers in infected leaf tissues from 2012 to 2016. These findings have implications for HLB management.</div>