Question

A yellow dragon disease threatens the citrus fruits in most countries . The responsible pathogen of the disease is a motile bacteria belongs to Candidatus Liberibacter spp and the size of causative gene that found in the chloroplast genome is 720 bp. A plant disease management team from Ministry of Agriculture and Fisheries request for your help to perform DNA analysis for 15 lime trees before being send to the plant nurseries around the country. Answer the following questions.

a. Why it is important to screen for bacterial infection in 15 lime trees?

b. Describe how you would detect the bacterial pathogen in 15 lime trees by DNA analysis?

Answer 1

a. Candidatus liberibacter spp infect plants such that they cause various metabolic changes after gaining entry into the phloem of the plant, causing disruptions in the transport of nutrients and in defense mechanisms. Moreover, such infections may not be conspicuously visible, especially when the symptoms are yet to be seen. Sending the lime trees which are possibly infected with Candidatus liberibacter spp to nurseries around the country would put other citrus plants in those nurseries at risk. Therefore, it is necessary to screen the 15 lime trees for infection before transfer.

b. DNA analysis for the pathogen will require extraction of nucleic acids from the plant extract followed by amplification of the 720 bp causative gene. Briefly, plant leaves would have to be chopped into a fine mince using a sterile razor blade and suspended into an extraction buffer. DNA from Chloroplasts would have to be isolated, and amplification of the 720 bp target would be performed by PCR using gene-specific primers. This would be followed by gel electrophoresis of the amplified PCR product. If bands corresponding to the 720 bp size are found in the gel after staining with Ethidium bromide or a similar dye, then it can be confirmed that the plant is infected with Candidatus.