ARTIFICIAL INOCULATION AND COLONIZATION OF DYERS WOAD (ISATIS-TINCTORIA) BY THE SYSTEMIC RUST FUNGUS PUCCINIA-THLASPEOS

Dyer's woad plants were inoculated successfully with the systemic rust fungus, Puccinia thlaspeos, using a dew chamber. At least 94% of plan ts became diseased when whole plants were inoculated, but only 28% bec ame diseased when single leaves were inoculated. The plants were asymp tomatic for at least 10 weeks after inoculation, but some remained asy mptomatic for as long as 9 months. Polymerase chain reaction was used to study asymptomatic colonization by the rust. After inoculation at t he leaf tip, P. thlaspeos moved through the leaf at a rate of about 0. 25 cm per week. By 10 weeks, the fungus had grown down the leaf, throu gh the petiole, and into new leaves produced by the plant. The fungus was detected in most leaves and in the roots of an overwintering roset te that was infected, but asymptomatic. P. thlaspeos likely invades wo ad through its leaves and moves into the meristematic areas and roots where it overwinters. Second-season plants, including the roots and as ymptomatic shoots, were completely colonized by P. thlaspeos after bol ting. Seed produced by diseased plants germinated as well as seed from controls.