Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/10/1999
Publication Date: N/A
Citation: Interpretive Summary: Chayote is a commercially important vegetable crop in Brazil, where it is affected by a disease known as chayote witches' broom. Symptoms of the disease suggested that it may be caused by a phytoplasma, which is a minute cell wall-free bacterium. We detected phytoplasma DNA in diseased plants of chayote by using a molecular method called the polymerase chain reaction. We analyzed this DNA to identify the phytoplasma, and we found that the chayote witches' broom disease phytoplasma is different from other phytoplasmas that have been reported previously. We report our classification of the phytoplasma and the nucleotide sequence of part of the ribosomal RNA operon of this phytoplasma. We also found that plants of Momordica charantia, which were growing as weeds in fields of chayote, were also infected by the chayote witches' broom disease pathogen. These findings provide insight for future development of methods to control the disease in chayote, and they provide molecular data that will be of interest to scientists, diagnostics companies, and organizations such as APHIS that are interested in preventing international movement of the pathogen in plant germplasms.
Technical Abstract: Chayote (Sechium edule Sw.) (Cucurbitaceae), also known as vegetable pear, mirliton or mango squash, is a commercially important vegetable crop in Brazil, where it is affected by chayote witches' broom disease. Affected plants exhibit witches' broom growths and other symptoms characteristic of plant diseases caused by phytoplasmas. Since previous electron microscopic cstudies revealed the association of a phytoplasma with chayote witches' broom, the present work was aimed at detecting and classifying the phytoplasma that may be the causal agent of the disease. Strains of a phytoplasma belonging to group 16SrIII (X-disease phytoplasma group) were discovered in chayote affected by witches' broom disease and in diseased plants of Momordica charantia L. that were growing as weeds in fields of chayote in Brazil. On the basis of results from restriction fragment length polymorphism and nucleotide sequence analyses of 16S rDNA, the phytoplasma was classified in a new subgroup, designated subgroup III-J. This classification was supported by a phylogenetic tree constructed by the Neighbor-Joining Method.