Lettuce reaction to black root rot caused by Thielaviospsis basicola

Lettuce is the most important leafy crop in Brazil. The varietal reaction of four lettuce types to lettuce black root rot (LBRR) caused by Thielaviopsis basicola at the juvenile stage were determined. The trial was carried out in controlled greenhouse conditions and arranged in completely randomized design, in a 37 x 2 (cultivars with and without inoculation) cheme with three replications. 30-day old seedling's were transplanted to styrofoam tray of 128 cells filled with 1/3 of colonized substrate with 7,5 x 10(5) conidia/g of substrate. After transplant, seedlings were reinoculated with a spore suspension with 2 x 10(6) conidia/mL poured next to the seedling stem. Host reaction to the pathogen and its evaluation were performed according to a severity scale from I (absence of symptoms) to 5 (more than 90% of rotted roots). Lettuce cultivars belonging to the loose leaf and batavia types were all resistant to LBRR. Cultivars of iceberg lettuce and butterhead types presented inter-varietal reactions being, some resistant and others susceptible.