Asymmetric Economic Impacts of Crop Genetic Resistance Gain and Loss: Evidence from Wheat Tan Spot Pathosystem

Safeguarding crop genetic resistance is essential for limiting disease impacts and maintaining agricultural productivity. The economic impacts of genetic resistance loss driven by pathogen adaptation have rarely been quantified. While developing improved varieties is an option in the event of resistance loss, this is a lengthy, uncertain and costly process, leaving few viable alternatives during epidemics. Furthermore, when disease resistance traits are overcome, growers rely more heavily on chemical inputs. This study develops a scalable analytical and Monte Carlo simulation-based framework to evaluate the economic impacts of a one-step change, either improvement or decline, in the rating of host genetic resistance to disease using the wheat-Pyrenophora tritici repentis pathosystem as a case study. The simulation considered disease resistance rating transitions, epidemic risk, proportion of yield lost to disease, quality downgrade risk and grower risk aversion under different yield potential scenarios. Results demonstrate that a one-step improvement in genetic resistance rating increased the expected discounted net benefits by 5.17 to 7.18%, whereas a one-step decline reduced net benefits by 5.57 to 8.10% depending on yield potential and epidemic conditions. Our findings highlight that the cost of genetic resistance loss outweighs the benefits from incremental genetic resistance gains, particularly under epidemic conditions, indicating the need to consider resistance as a core agricultural capital in genetic innovation. Failure to protect existing resistance increases reliance on chemical measures of crop protection, the risk of chemical resistance development and vulnerability to epidemics, with significant implications for long-term farm viability.