|Liu, Hsing yeh|
Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/13/2001
Publication Date: 8/1/2001
Citation: Interpretive Summary: The recently observed dieback disease of lettuce in California and Arizona is caused by a previously undescribed strain of TBSV. This strain of TBSV is also responsible for a new disease of greenhouse-grown tomatoes in the southwestern U.S. Pathogenicity tests conducted by soil-inoculation of lettuce plants with the TBSV-Lettuce strain together with the pathogen association data suggest that TBSV is the cause of dieback disease in lettuce. Portions of the genomes of several tombusvirus isolates have been sequenced and have been found to be helpful in classification and strain differentiation of tombusvirus isolates. We used primers specific for the 3'-terminus of tombusvirus genomes for cloning of parts of the genomic RNA. A phylogenetic tree based on the genetic distance data for the 3'-terminal genomic nucleotide sequence of all our isolates was made. Two serologically distinct major TBSV strain groups have been described previously, the TBSV- -Cherry strain and the TBSV-BS3 strain. Some of the isolates obtained from lettuce with dieback symptoms cluster with high significance together in a third new TBSV-Lettuce strain group. This group is significantly distinct in 3'-terminal genomic nucleotide sequence composition from previously described TBSV strains or isolates (12-17% genetic distance), but more closely related to TBSV strains than to CNV (33% genetic distance). An understanding of tombusvirus genome diversity under agricultural conditions is needed to draw epidemiological conclusions from isolates obtained from different fields or agricultural areas.
Technical Abstract: An economically significant disease that causes necrosis and dieback of lettuce was found in increasing frequency in California and Arizona in recent years. An isometric virus serologically related to Tomato bushy stunt virus (TBSV) was consistently isolated from diseased lettuce plants. Back-inoculation to healthy lettuce plants and subsequent reisolation of the virus from symptomatic lettuce leaves implicated TBSV as the causal agent. A tombusvirus isolated from symptomatic tomato was found to be responsible for a necrosis-inducing disease of greenhouse-grown tomato in Colorado and New Mexico. Clones derived from a portion of the 3'-end of viral genomic RNAs recovered from lettuce and tomato revealed identical sequences, but 12-17% genetic distance to previously described TBSV strain sequences. However, some virus isolates recovered from diseased lettuce and tomato plants were closely related to previously described TBSV strains and dto Cucumber necrosis virus (CNV). Western blot analysis using tombusvirus- specific antiserum compared to newly produced antiserum to a TBSV-Lettuce isolate revealed that the most frequently recovered tombusvirus from diseased lettuce and tomato plants in the Southwestern United States is serologically distinct from previously described tombusviruses and should be considered as a new strain of TBSV.