Abstract

Horseradish internal root discoloration (IRD) is a disease complex caused by several different soil-borne fungal pathogens and is the most important disease problem that affects horseradish worldwide, since it directly influences root marketability. Horseradish growers in North America have experienced yield losses up to 100% due to this disease complex. In Illinois, USA, horseradish is a major specialty crop that is grown in the southwestern part of the state near St. Louis, Missouri, and this region is considered the most concentrated horseradish production region in the world. Both Southern Illinois University-Carbondale and University of Illinois-Champaign have worked together during the last 20 years toward the development of improved horseradish varieties with IRD tolerance. The purpose of this study was twofold, first to evaluate current commercially grown horseradish clones for their tolerance to IRD under field conditions, and then to determine the suitability of clones found most tolerant for developing new improved cultivars with IRD tolerance. Most horseradish clones evaluated in IRD infested fields near Collinsville, Illinois, were highly susceptible, with only 15K having consistent field tolerance. This clone has previously been observed under commercial field conditions by the author and several other sources to have some tolerance to IRD. Other horseradish clones that may have some potential IRD tolerance under field conditions were 315, 7586, and 9705, based on the IRD incidence and/or IRD symptom severity that developed in the roots based on this study. Two horseradish clones (15K and 315) were shown to be highly effective as parents for developing new cultivars having IRD tolerance. Breeding for tolerance to this disease complex has been the major focus in new horseradish cultivar development in Illinois, USA for the last several decades, which have included using 15K and 315 as parents to develop improved cultivars with IRD tolerance. The continued success of the Illinois, USA horseradish industry depends on the breeding program to provide growers with new selections having increased vigor, outstanding root quality, high yields and IRD tolerance.

Keywords:Armoracia rusticana; Breeding; Fusarium; Variety development; Verticillium