A Soilless Verticillium Wilt Assay Using an Early Flowering Lettuce Line

A soilless growth chamber assay was evaluated for rapid assessment of Verticillium wilt on lettuce (Lactuca sativa). Seedlings of the early flowering Plant Introduction (PI) 251246 were inoculated in tubes with conidial suspensions of isolates of Verticillium dahliae from lettuce or cauliflower. PI 251246 developed significant leaf and root symptoms by 21 days following inoculation with isolates of race 1 and race 2 from lettuce, but not following inoculation with an isolate from cauliflower. In contrast, leaf symptoms on the cultivar La Brillante and root symptoms on the cultivar Salinas were not easily differentiated from the symptoms observed on the noninoculated control treatments in the soilless assay, even at the highest inoculum concentration of 1 × 10⁷ conidia/ml. Comparison of the soilless growth chamber assay and a soil-based greenhouse assay revealed a significantly higher proportion of PI 251246 with root vascular discoloration in the soilless assay compared with the soil-based greenhouse assay (χ², 1 df = 8.9; P = 0.003). There is thus an advantage to using the soilless growth chamber assay with PI 251246. Compared with the soil-based greenhouse assay, the soilless assay reduced the time required for evaluation of Verticillium wilt symptoms on lettuce from about 90 days to 42 days.