Identification and phylogenetic analysis of a new phytoplasma from diseased chayote in Brazil

Chayote (Sechium edule) (Cucurbitaceae), also known as vegetable pear, mirl iton, or mango squash, is a commercially important vegetable crop in Brazil , where it is affected by chayote witches'-broom disease. Affected plants e xhibit witches'-broom growths and other symptoms characteristic of plant di seases caused by phytoplasmas. Since previous electron microscopic studies revealed the association of a phytoplasma with chayote witches'-broom, the present work was aimed at detecting and classifying the phytoplasma that ma y be the causal agent of the disease. Strains of a phytoplasma belonging to group 16SrIII (X-disease phytoplasma group) were discovered in chayote aff ected by witches'-broom disease and in diseased plants of Momordica charant ia that were growing as weeds in fields of chayote in Brazil. On the basis of results from restriction fragment length polymorphism and nucleotide seq uence analyses of 16S rDNA, tbe phytoplasma was classified in a new subgrou p, designated subgroup III-J. This classification was supported by a phylog enetic tree constructed by the Neighbor-Joining method.