Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 9/4/2001
Publication Date: N/A
Technical Abstract: Sixty-five single spore isolates of <i>Cercospora beticola</i>, the fungus causing Cercospora leaf spot of sugarbeet, were evaluated for tolerance to triphenyltin hydroxide, a common fungicide used to control leaf spot disease. Twenty-two isolates tested in the study exhibited tolerance to TPTH at a 10 ppm level, whereas, 43 isolates exhibited sensitivity to 5 ppm TPTH. Genomic DNA prepared from these and additional <i>C. beticola</i> isolates, as well as from <i>C. kikuchii</i> and <i>C. zeae-maydis</i>, was subjected to amplified fragment length polymorphism (AFLP) and random amplified polymorphic DNA (RAPD) analysis. Thirteen AFLP markers and one RAPD marker were used to evaluate isolate relatedness by the unweighted pair group method using arithmetic averages (UPGMA). The results indicate that significant genetic diversity exists within <i>C. beticola</i> isolates in the U.S. and little geographic isolation of isolate types has occurred. Cross- examination of isolate tolerance to TPTH with AFLP data revealed two molecular markers highly associated with high fungicide tolerance. The results are discussed in relation to the difficulty in breeding for resistance to <i>C. beticola</i> in sugarbeet and in the rapid development of fungicide tolerance in this imperfect fungus.