Emails: lamia.aouini@kaust.edu.sa, yjwang@cemps.ac.cn, emile.cavaletgiorsa@kaust.edu.sa, michael.abrouk@kaust.edu.sa, esther.jung@botinst.uzh.ch, bkeller@botinst.uzh.ch, simon.krattinger@kaust.edu.sa

The effective deployment of disease resistance (R) genes is one of the most important topics in wheat disease resistance breeding. Many R genes are influenced by genetic backgrounds. Although ‘genetic background effects’ are well documented in literature, the underlying genetic and molecular mechanisms are only poorly understood.

Our study focusses on the leaf rust resistance gene Lr14a that encodes an unusual protein consisting of twelve N-terminal ankyrin repeats and a C-terminal transmembrane domain. Noticeably, Lr14a is strongly influenced by the genetic background. Certain wheat cultivars were fully susceptible to leaf rust despite the presence of Lr14a.

Here, we used two contrasting, Lr14a-containing near-isogenic wheat lines, ArinaLr14a and ArinaLrFor, which differed in their responses to leaf rust at seedling stage. While ArinaLrFor exhibited the characteristic mesothetic Lr14a-type of resistance at seedling stage, ArinaLr14a was fully susceptible. Segregation analysis in an ‘ArinaLr14a X ArinaLrFor’ mapping population indicated the segregation of a single modifier gene that was mapped to chromosome arm 1BS.

Interestingly, the identified 1BS genomic region overlapped with the previously reported Lr75 gene. Lr75 was identified as a minor adult plant resistance gene in ArinaLrFor. Our results indicate that the Lr14a seedling modifier and the Lr75 adult plant resistance gene might be identical. Our research highlights the importance of disease resistance modifiers and provides the basis to fine-tune leaf rust resistance in the future.