Lesion Mimic in Wheat Is Associated with Elevated Adult Plant Resistance to Leaf Rust.

Lesion mimic (LM) that resembles plant disease symptoms in the absence of pathogen attack may confer enhanced disease resistance to a wide range of pathogens. Wheat line Ning7840 shows LM phenotype. To elucidate the relationship between LM and leaf rust resistance, a gene responsible for LM was mapped to the distal region of chromosome 1BS in three experiments using a population of 182 recombinant inbred lines (RILs) derived from the cross Ning7840/Chokwang. Chokwang is a Korean wheat cultivar that does not express the LM symptom. Segregation ratio of LM and non-LM RILs fits 1:1 Mandelian single gene segregation (X²=1.39, P=0.24). The RIL population was inoculated with virulent leaf rust isolate Amadina (Puccinia triticina) at anthesis in greenhouse. Also the population was natural infected under field conditions. Significant phenotypic correlations (r=-66.57, P<0.0001) were observed between LM symptom and rust severity among RILs. Those lines with LM showed significant elevation of adult-plant resistance to leaf rust compared to that of non-LM lines (t=11.90, P<0.0001). Composite interval mapping (CIM) detected a QTL Qlr.pser.1B for leaf rust resistance on chromosome 1B in both experiments. This QTL overlapped with the gene for LM, and explained 55.47% of phenotypic variation for leaf rust resistance in two experiments. The results suggest that the gene for LM is most likely also responsible for leaf rust resistance with pleiotropic effects. Further investigation of LM pathway may facilitate identification of new mechanisms of broad-spectrum disease resistance