ARS | Publication request: A soilless Verticillium wilt assay using an early flowering lettuce

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 27, 2009
Publication Date: July 1, 2009
Citation: Klosterman, S.J., Hayes, R.J. 2009. A soilless Verticillium wilt assay using an early flowering lettuce. Plant Disease. 93:691-698,2009.

Interpretive Summary: Verticillium wilt of lettuce is caused by the fungus Verticillium dahliae. Different concentrations of the fungus were tested for their ability to cause disease symptoms in a test tube system using three different types of lettuce with the goal of developing a convenient assay of Verticillium wilt of lettuce under controlled conditions. The assay takes advantage of the early flowering lettuce plant introduction line PI 251246, which develops symptoms more quickly than other lettuce varieties. The study demonstrates that the method is not useful for selecting different plant cultivars resistant to Verticillium wilt. However, because the pathogenicity assay using the early flowering line PI 251246 is more rapid and uses less space, this method will allow more convenient testing of fungal genetic mutants for their ability to infect and colonize lettuce.

Technical Abstract: A soilless growth chamber assay was evaluated for rapid assessment of Verticillium wilt symptoms on lettuce. Seedlings of the early flowering plant introduction (PI) 251246 were inoculated in tubes with conidial suspensions of Verticillium spp. isolates from lettuce or cauliflower. PI 251246 developed leaf and root symptoms at 21 days following inoculation with all V. dahliae isolates from lettuce, but not following inoculation with the cauliflower isolate. In contrast, leaf wilt symptoms in crisphead cultivars Salinas and La Brillante were not easily differentiated from scenescent leaves in the soilless assay, even at the highest inoculum concentration. The results of the soilless assay and a traditional greenhouse assay were compared. PI 251246 seldomly developed leaf symptoms in the greenhouse environment at three weeks after inoculation. Additionally, there was a reduction in the numbers of plants with root discoloration in the greenhouse-based assay. There is thus an advantage to using the early flowering line PI 251246 in a soilless assay. The use of PI 251246 in the soilless assay provides a convenient and rapid method to analyze virulence of V. dahliae on lettuce.