() Mediates f. sp. Race 1 Avirulence on -Resistant Strawberry Cultivars.

f. sp. () race 1 is avirulent on cultivars with the dominant resistance gene , while race 2 is virulent on -resistant cultivars. We hypothesized there was a gene-for-gene interaction between a gene at the locus and an avirulence gene () in race 1. To identify a candidate , we compared genomes of 24 race 1 and three race 2 isolates. We found one candidate gene that was present in race 1, was absent in race 2, was highly expressed in planta, and was homologous to a known effector, (). We knocked out in two race 1 isolates by homologous recombination. All knockout transformants (Δ) gained virulence on cultivars, whereas ectopic transformants and the wildtype isolates remained avirulent. Δ isolates were quantitatively less virulent on cultivars Fronteras and San Andreas than cultivars. Seedlings from an × population were genotyped for and tested for susceptibility to a knockout isolate. Results suggested that additional minor-effect quantitative resistance genes could be present at the locus. This work demonstrates that acts as an avirulence factor interacting with a resistance gene at the locus. The identification of enables surveillance for race 2 and provides insight into the mechanisms of mediated resistance. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.