Spatial point pattern analysis of Candidatus Liberibactor asiaticus diagnostics from Asian citrus psyllid (Diaphorina citri Kuwayama) samples: Potential for predicting infected citrus host locations

An opportunity to analyze spatial patterns to determine the underlying biological process has developed from the wide spread sampling and testing of Asian citrus psyllids in Texas and California to locate early infections of huanglongbing (HLB) disease.  The real-time polymerase chain reaction diagnostic methods used to detect the casual agents of HLB, Candidatus Liberibacter asiaticus (cLas), are set to run for 40 cycles.  The reaction must surpass a set threshold of ≤ 32 prior to the completion of the run to be considered positive for the presence of cLas.  Currently, reactions that surpass the threshold at 33 or more cycles have proven impossible to acquire confirmatory conventional PCR bands and DNA sequence data.  Thus, these samples are classified as inconclusive. The question we are trying to answer is whether information in the Ct-values between 33 and 40, is also useful for predicting locations with HLB infected citrus plants.  In both Texas and California spatial clustering of psyllid samples with inconclusive Ct-values have been shown to cluster around known positive HLB infected trees.