Evaluation of Verticillium Wilt Resistance in Russet Norkotah and Six Strain Selections

Strain selections of Russet Norkotah have been selected for enhanced vigor and high yield. In addition, they exhibit less severe expression of disease symptoms in the presence of Verticillium dahliae , a soil-borne fungal pathogen that causes Verticillium wilt. However, this apparent resistance may be due to later maturity in the strain selections. This study was designed to compare the levels of Verticillium wilt resistance in Russet Norkotah with that of six popular strain selections. In two years, trials were carried out on a V. dahliae -infested field and an adjacent fumigated field. Comparisons were made between Russet Norkotah and its strains for maturity, symptom expression, stem colonization, and tuber yield. Compared to Russet Norkotah, the strains were later in maturity, exhibited fewer Verticillium wilt symptoms, and were higher yielding in the absence of V. dahliae . However, they were similar to Russet Norkotah in stem colonization and yield in the presence of the pathogen. Apparent resistance in the strain selections appears to be due to immature plant physiology rather than their ability to limit fungal growth and reproduction in stem tissues.