This soil fungus, along with Pythium species, can sometimes cause damping-off of lettuce. Seedlings may be killed before or just after emergence.
Infected seedlings exhibit decayed roots and brown lesions on stems.
When seedlings are infected, the stem tissue collapses and plants fall over and die. In some areas, particularly the San Joaquin Valley and desert areas, R. solani infects lettuce plants as the heads begin to form. Brown, sunken lesions form on the midribs that are in contact with the soil. As the disease progresses, the fungus will infect leaves inside the head. Soft rots, due to secondary decay organisms, will often develop on bottom rot infection sites, resulting in collapse of the head.