Response of six potato cultivars to amount of applied water and Verticillium dahliae

Six potato cultivars were grown with or without the addition of Verticilliu m dahliae inoculum and were watered at 50, 75, or 100% estimated consumptiv e use. The applied water x cultivar interaction was significant (P = 0.009 and P = 0.001 for 1996 and 1997, respectively) for the relative area under the senescence progress curve (RAUSPC). With a decrease in water, there was an increase in RAUSPC. A significant interaction of inoculum density x cul tivar also was found, based on RAUSPC (P = 0.0194 and P = 0.0033 for 1996 a nd 1997, respectively). In V. dahliae infested plots, 'Katahdin' and 'Range r Russet' were resistant to Verticillium wilt. Population size of V.! dahli ae in stem apices was significantly lower in 'Katahdin' in both 1996 and 19 97 (P = 0.0001) and in 'Ranger Russet' in 1997 (P = 0.0001) than in the oth er cultivars. 'Russet Burbank' and 'Shepody' had large apical stem populati ons of V. dahliae and higher RAUSPC values associated with both R dahliae i noculum and decreased amount of applied water. Marketable tuber yield was u naffected by R dahliae in both years. Cultivar resistance to Verticillium w ilt was related to cultivar tolerance to moisture deficit stress. Results s uggest that moisture deficit stress response has the potential to be a usef ul tool in protocols for screening potato for Verticillium resistance.