Genetic analysis of durable leaf rust resistance in winter wheat

Quantitative resistance that delays the epidemic development of leaf rust i n wheat is an important source for durable resistance breeding. The Swiss w inter wheat variety 'Forno' shows a high level of quantitative resistance a gainst leaf rust. This resistance has been effective for more than 10 years and can therefore be considered to be durable. In order to map quantitativ e trait loci (QTL) for durable leaf rust resistance we analysed 204 F-5 rec ombinant inbred lines (RILs) of the cross between the winter wheat 'Forno' and the winter spelt 'Oberkulmer' for their level of leaf rust resistance ( LR) and leaf tip necrosis (LTN) in four different environments. Both traits showed a continuous distribution and were significantly correlated (r=-0.5 ). Across environments we detected 8 QTL for leaf rust resistance (6 inheri ted from 'Forno') and 10 QTL for the quantitative expression of LTN (6 inhe rited from 'Forno'). Of the 6 QTL responsible for the durable leaf rust res istance of 'Forno', 1 major QTL coincided with a thaumatin locus on 7BL exp laining 35% of the phenotypic variance. Four QTL for LR coincided with QTL for LTN. At these loci the alleles of 'Forno' increased the level of resist ance as well as the extent of LTN, indicating pleiotropy.