Response of potato cultivars to plant available water and Verticillium dahliae

摘要

Verticillium wilt, caused by the soilborne fungus Verticillium dahliae Kleb, is a factor limiting potato production in both irrigated and non-irrigated production areas in the United States. Yield reductions of up to 46 percent have been reported (2,6). This disease becomes severe when potatoes have been cropped on the same ground for several years (13). In several production areas it is effectively controlled by soil fumigation (1). With new chemical restriction laws coming into effect, efficacy of cultural practices such as green manuring and irrigation management are being addressed as possible alternatives. To date, few cultivars have acceptable levels of resistance to this disease. The relationship between soil moisture status and severity ofVerticillium wilt in production systems of several crops has been inconsistent. For example, severity of wilt symptoms has been associated with amount of applied water, frequency of irrigation and drought episodes. Cappaert et al. (2) showed with an increase in amount of applied water there was an increase in severity of potato early dying in potato cv Russet Burbank. In cotton (7) an increase in amount of applied water resulted in an increase in severity of disease symptoms, due to more frequent and earlier initiation of irrigation. With 'guyule' (rubber tree), disease increased when irrigation frequency was increased but amount of applied water remained the same across irrigation frequencies (14). In contrast, the severity of Verticillium wilt in maple increased under soil moisture deficit stress (4) when soil moisture was maintained at constant levels, and conversely, the degree of wilt decreased as the sapwood water increased. In work by Nelson (12), mint grown in plots that were held at 70 percent of field capacity had higher disease ratings than mint grown in plots held at 85 percent of field capacity. Studies are limited on the interaction between moisture deficit stress and resistance to Verticillium wilt in a range of potato cultivars. Ourworking hypothesis is cultivars that are tolerant to moisture deficit stress will be resistant to Verticillium wilt. Therefore, the objectives of our research were to identify potato cultivars that tolerate moisture deficit stress, measure cultivar responses to Verticillium, and establish if cultivar responses to these stresses are related.