Durability of quantitative resistance in crops: Greater than we know?

Authors: Cowger, Christina; BROWN, JAMES - John Innes Center

Submitted to: Annual Review of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2019
Publication Date: 8/1/2019
Citation: Cowger, C., Brown, J.K. 2019. Durability of quantitative resistance in crops: Greater than we know? Annual Review of Phytopathology. 57:253-277.

Interpretive Summary: Quantitative resistance (QR) to crop diseases, which is partial, has usually been more long-lasting than resistance that comes from major genes than major-gene resistance which is initially fully or near fully effective against some strains of a pathogen. Some QR has eroded as pathogens adapted to it, especially when the QR is widely used in agriculture and epidemics of the pathogen are frequent. Changes in aggressiveness of various plant pathogens on crop cultivars with QR have been observed, and there are experimental data on the effects on pathogen fitness (disease-causing and reproductive ability) of adaptation to QR. However, there is little information about the molecular basis of pathogen adaptation to QR. Some QR has protective effects against multiple diseases, while in a few cases QR can have a positive effect against one disease but lead to greater susceptibility to another. Data on cultivars’ disease ratings in field experiments over several years can be used to understand how durable QR is in crops. It is argued that published data likely under-report the durability of QR, because cases where pathogens do not become more aggressive on QR cultivars are not reported. The implications of research on QR for plant breeding are discussed.

Technical Abstract: Quantitative resistance (QR) to crop diseases has usually been much more durable than major-gene, effector-triggered resistance. It has been observed that the effectiveness of some QR has eroded as pathogens adapt to it, especially when deployment is extensive and epidemics occur regularly, but it generally declines more slowly than effector-triggered resistance. Changes in aggressiveness and specificity of diverse pathogens on cultivars with QR have been recorded, along with experimental data on fitness costs of pathogen adaptation to QR, but there is little information about molecular mechanisms of adaptation. Some QR has correlated or antagonistic effects on multiple diseases. Longitudinal data on cultivars’ disease ratings in trials over several years can be used to assess the significance of QR for durable resistance in crops. It is argued that published data likely under-reports the durability of QR, owing to publication bias. The implications of research on QR for plant breeding are discussed.