Specific and Accurate Detection of the Citrus Greening Pathogen Candidatus liberibacter spp. Using Conventional PCR on Citrus Leaf Tissue Samples.

Citrus greening, also known as huanglongbing, is a destructive citrus disease ravaging citrus farms globally. This disease causes asymmetrical yellow leaf mottling, vein yellowing, defoliation, root decay, and ultimately, the death of the citrus plant. When infected, the citrus plants have stunted growth and produce flowers out of season. These flowers rarely yield fruit, and those that do yield small, bitter, irregularly shaped citrus fruit that are not desirable. This disease is spread by the Asian citrus psyllid, Diaphorina citri, and by the grafting of infected citrus tissue. The pathogen has a long and variable incubation period within the citrus plant-sometimes years, before symptoms appear. Attempts to culture this pathogen in vitro have been unsuccessful, possibly due to the low and uneven concentration of the pathogen within infected citrus tissue, or because it is difficult to replicate the environmental conditions conducive to growth of the pathogen. It is very difficult to identify the disease before it has spread, due to its long incubation period and researchers' inability to culture the pathogen. As a result, the disease only becomes apparent after suddenly destroying a citrus farmer's entire yield. Presented here is a method for the accurate and specific detection of the citrus greening pathogen, Candidatus liberibacter spp. using a genomic DNA extraction kit and PCR. This method is simple, efficient, cost effective, and adaptable for quantitative analysis. This method can be adapted for use on any citrus tissue; however, it is potentially limited by the amount of pathogen present in the tissue. Nevertheless, this method will allow citrus farmers to identify infected citrus plants earlier, and curb the spread of this destructive disease before it can further spread.