Race-Specific Resistance Genes Against <em>Erysiphe gramminis</em> f. sp. <em>hordei</em> in Old and Recent French Barley Accessions.

Leaf segments from seedlings of 68 old barley varieties and 38 more recent cultivars of past or current importance in France were infected with 6--9 powdery mildew isolates in order to identify race-specific resistance genes. No resistance gene was apparent in the 21 old winter varieties, 43 of 47 old spring varieties, 10 recent winter and 3 recent spring cultivars. Two old spring varieties (`Colmar S 142' and `Johanna') were postulated to have Mlg and Ml(CP), and two others (`Pontrieux' and `Finistère 62-5') had an unidentified, weakly effective gene. Mlg, Ml(CP), Mlb, Mla6 and Mla13 were the only genes detected in recent winter cultivars. Recent spring cultivars presented the greatest diversity; the presence of one or several genes among Mla1, Mla6, Mla9, Mla12, Mlg, Ml(CP), Ml(La), Mlk and mlo was postulated in several lines. [ABSTRACT FROM AUTHOR]