Vectors of Phytoplasmas

Phytoplasmas are phytopathogenic Mollicutes. These minute wall-less bacteria are found exclusively in phloem and primarily on sieve elements and cannot be cultured artificially. They were first associated with “yellows” diseases in 1926, although at the time they were thought to be viruses. Since then, phytoplasmas have been found in hundreds of plant species. Over 300 plant diseases are known worldwide, including economically important flowers, vegetables and orchards.

Phytoplasmas are vectored from plant to plant by a select group of Hemipterans feeding in the phloem. Of these insects, the leafhoppers and planthoppers have been shown to vector phytoplasmas, and more recently, a psylla (Bactericera trigonica) has been shown to vector phytoplasmas in carrots.

Once an insect has fed in the phloem of a phytoplasma-infected plant, a number of events must take place for it to be a successful vector. There are a number of anatomical and physiological barriers that the phytoplasma must...