Resistance of wheat cultivars and breeding lines to septoria tritici blotch caused by isolates of Mycosphaerella graminicola in field trials

Isolate-specific resistance of 71 cultivars and breeding lines of wheat (Tr iticum aestivum) to septoria tritici blotch was evaluated in six field tria ls in the Netherlands, Switzerland and the UK between 1995 and 1997. Each p lot was inoculated with one of six single-pycnidium isolates of the pathoge n Mycosphaerella graminicola. There were strong interactions between wheat lines and M. graminicola and the line-by-isolate interactions were stable o ver the six trials. Lines with specific resistance or specific susceptibili ty to each of the isolates were identified. Specific resistance to isolate IPO323 was especially common, being carried by 22 lines from 10 countries. The results confirm that line-by-isolate interactions in septoria tritici b lotch of wheat are effective in adult plants in field conditions, and are n ot simply confined to seedlings. Wheat lines with good, quantitative resist ance to all or most isolates were identified, including lines from Brazil, the USA and seven European countries. These may be useful as sources of res istance in wheat breeding.