Evaluation of potato clones for severity of Verticillium wilt, yield and specific gravity in Maine

In 1994 and 1995, the effect of Verticillium milt, caused by Verticillium dahliae and V. albo-atrum, on tuber yields, number and weight of U.S. No. 1 and B size tubers, and specific gravity was studied in northern Maine, an area with a short growing season. Seven clones (four resistant and three susceptible) were evaluated in a split-plot design with three replications, Clones were the whole-plot factor, and seed pieces in sub-plots were either uninoculated or inoculated with 50 ml of 4 x 10(4) cfu/ml Verticillium spp. at planting. Individual plants mere scored for Verticillium wilt symptoms before harvest on a 1= <3% wilt to 10= <97% wilt. Differences among clones for wilting and specific gravity were significant. The inoculation treatment had no effect on any of the tuber traits measured. However, there mere significant clone x inoculation interactions for most tuber traits, Reductions in yield, weight and number of U.S. No. 1 potatoes, and specific gravity were greater in the Verticillium wilt susceptible clones than in the resistant clones. These results suggest that breeding clones with resistance to Verticillium spp. will reduce yield losses, while maintaining tuber size and specific gravity under disease pressure.