First report of the breakdown of the YR17 resistance gene to wheat stripe rust in the Grand Duchy of Luxembourg

Abstract

Yr17 resistance gene (Yr17+ cultivars) induces yellow rust resistance in wheat at the seedling stage and operates throughout the plant life. A new Yr17 pathotype that overcomes resistance to wheat stripe rust in Yr17+ cultivars was first detected in 1997 in countries neighboring Luxembourg (Bayles et al., 2000). In 1999, stripe rust was suspected to occur also in this country (GDL) and, in 2003, Puccinia striiformis f. sp. tritici was identified. Disease severity was recorded in the 1999-2009 period in fungicide untreated experiments with various cultivars grown in Everlange, Christnach, Burmerange and Reuler (El Jarroudi et al., 2009). Over this 11-year period, the difference between Yr17+ (Achat, Akteur, Astron, Flair) and Yr17- (Aron, Batis, Bussard, Drifter, Ritmo,Vivant) cultivars was highly significant, the highest severity being observed in Yr17+ cultivars (mean severity of 13%) compared to Yr17- cultivars (0.2%). In 1999, Yr17+ cultivars showed the highest disease severity (19%) whereas in 2000 and 2001, the highest severity was observed in cv. Flair (Yr 17+) with 30% and 22%, respectively at Everlange, and 50% and 11%, respectively at Christnach. In both years symptoms on Yr17- cultivars were rare (severity <1%) or absent. During 2002-2009 yellow rust occurred with relatively low severity (average 6%) on Yr17+ cultivars (cv. Achat at Everlange in 2002, 2008 and 2009, cv. Akteur at Everlange and Reuler in 2007). These observations support the hypothesis of the presence in GDL of the Yr17 pathotype that overcomes the Yr17 gene. This new virulent pathotype appears more aggressive on Yr17+ than Yr17- cultivars. Since most resistant European cultivars are Yr17+, this renders control strategies based on this monogenic resistance to wheat stripe rust vain. Bayles R.A., Flath K., Hovmoller M.S., De Valavieille-Pope C.,. 2000. Breakdown of the Yr17 resistance to yellow rust of wheat in Northern Europe. Agronomie 20: 805-811. El Jarroudi M., Giraud F., Vrancken C., Junk J., Tychon B., Hoffmann L., Delfosse P,. 2009. First report of wheat leaf rust in the Grand Duchy of Luxembourg and the progress of its appearance over the 2003-2008 period. Plant Disease 93: 971-971.