|Lee, Ing Ming|
Submitted to: International Organization for Mycoplasmology
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2002
Publication Date: N/A
Technical Abstract: In 2000, an outbreak of aster yellows in carrots occurred in southwestern Texas. An epidemiological survey indicated that several vegetable crops including cabbage, onion, parsley and dill, and some weeds were also infected by aster yellows phytoplasmas. Ecological aspects of phytoplasmas involved in the epidemic were investigated. Nested PCR and RFLP analysis of PCR amplified phytoplasma 16S rDNA revealed that phytoplasmas belonging to two subgroups, A (16SrI-A) and B (16SrI-B), in the aster yellows group (16SrI), were predominantly detected in infected plants. Carrot, parsley, and dill were infected by both subgroups. Onion and three species of weeds (prickly lettuce, lazy daisy, and false ragweed) were exclusively infected by a subgroup A phytoplasma strains, while cabbage was infected by subgroup B phytoplasma. Both types of phytoplasmas were detected in the three leafhopper species (Macrosteles fascifrons, Scaphytopius irroratus and Ceratagallia abrupta) commonly present in this region during the period when the epidemic occurred. Nested PCR assays using group I and subgroup specific ribosomal protein (rp) primers revealed that an individual plant or insect could be doubly infected by both subgroup A and B phytoplasma strains. Mixed infections were very common in carrot, parsley, dill and the three leafhopper species. Phylogenetic analyses based on both 16S rDNA and rp gene sequences indicated that phytoplasma strains within subgroup A or subgroup B, which were associated with various plant species and putative insect vectors, were relatively homogeneous. Based on rp gene sequences, a new rp subgroup N was detected in some infected onions and in one leafhopper.