Phytoplasma

Phytoplasmas in a phloem cell of a plant

Phytoplasmas are bacterial plant pathogens that cause significant losses in agricultural production worldwide. They are causing a wide variety of symptoms that can range from mild yellowing to the death of infected plants. They are most prevalent in the tropical and sub-tropical regions of the world. Phytoplasmas are transmitted by hemipteran insect vectors such as leaf hoppers, in which the bacteria are also able to survive and replicate.

Phytoplasmas infect over 200 plant species, prominent examples are coconut, sugarcane, and sandalwood. They are are considered of quarantine relevance e.g. in the EU, which means that their spread is especially tightly regulated. There are no fully resistant crop varieties currently available. Therefore, main disease management strategies are limited to control of the vectors provided that those are known, and the elimination of infected plants. There is a great need for reliable and efficient methods for identification for this group of pathogens, and our standard barcoding regions are likely inefficient.

Witches' broom caused by Phytoplasmas

A group of European researchers tested a set of primers amplifying a fragment of the so-called tuf gene (Elongation factor Tu) for their potential to serve as a DNA barcode for phytoplasmas. Elongation factor Tu is a key protein involved in the process of protein biosynthesis. Standard in DNA-based bacterial identification is 16S rRNA. Analysis and alignments showed that important groups of phytoplasmas could readily be identified. While being shorter, the tuf barcode provided clear resolution at both group and subgroup levels compared to the 16S rRNA gene making it an ideal candidate.

This work was part of the QBOL initiative, which aims to develop a DNA barcode-based identification system for pests and pathogens with a focus on quarantine organisms. The project has started to release data in a specific database - q-bank.