* Email: bkeller@botinst.uzh.ch

Race-specific resistance (R) genes have played an important role in breeding against obligate biotrophic pathogens that cause diseases such as powdery mildew or rust in wheat. However, such genes are frequently overcome after being introduced into agricultural use. We have recently found that novel R genes can be efficiently identified in landraces held in genebanks based on geographical and environmental information. Landraces from Turkey, Iran and Pakistan have revealed a sursprising diversity of powdery mildew resistance genes.

Given the adaptive potential of fungal pathogens, we are also actively developing strategies to improve the use of race-specific R genes in wheat breeding and agriculture:

First, we want to diversify the molecular basis of disease resistance beyond NLR-based immune receptors. We have identified a novel chimeric kinase-MCTP protein encoded by the Pm4 race-specific R gene. Notably, the Pm4 gene has recently been found to confer resistance not only to powdery mildew, but also to wheat blast, opening exciting new avenues of research to develop combined resistance to two pathogens. In addition to the non-canonical Pm4 immune receptor, we recently identified the WTK4 tandem kinase as the product of a race-specific, powdery mildew resistance gene. Besides characterizing Pm4 and WTK4 function, we have developed an innovative mutagenesis approach in powdery mildew. We have identified the pathogen factors AvrPm4 and AvrWTK4, recognized by Pm4 and WTK4, respectively. Thus, there are successful initial attempts to understand the molecular basis of non-NLR based, race-specific wheat immunity.

Second, we are exploring several approaches to improve NLR-based resistance: one of them relies on the monitoring of avirulence genes to predict, based on pathogen-derived information, the potential durability of genes newly introgressed into wheat from wild species or wheat crop relatives.

We propose that the identification and monitoring of avirulence gene diversity in pathogen populations becomes an integral part of introgression breeding to ensure effective and durable resistance in wheat. Moreover, the knowledge of the wheat-fungal pathogen “interactome” promises to support breeding strategies for increased durability of resistance. We are also combining transgenic, overexpressed NLR genes to improve the durability of resistance.

Such combined (“pyramided”) genes have shown very good, long-term resistance in the field and represent promising new genotypes for breeding. Finally, we present a recent approach broadening NLR receptor specificity which was achieved by the improved molecular understanding of avirulence protein-NLR interactions.