Wilt and vascular root rot (Pythium tracheiphilum) of lettuce in Bah韆 Blanca, Argentina

A new disease of lettuce has been observed in the sur- roundings of Bahia Blanca, Argentina. The symptoms include dwarf- ing, general chlorosis, wilting, root rot, and leaf blight, sometimes fol- lowed by plant death. Pythium tracheiphilum Matta was found to be consistently associated with those symptoms. The morphological and morphometric characteristics of this oomycete are described. Isolates obtained from field-infected lettuce plants were inoculated to lettuce and caused similar symptoms as those found in natural infections. Seedling emergence was also severely affected following experimen- tal inoculation. Koch's Postulates were fulfilled by recovering the fun- gus from inoculated plants. The new disease shows a high destructive potential but currently has a limited prevalence and incidence.