Breeding new crop varieties with resistance to the biotic stresses that undermine crop yields is tantamount to increasing the amount and quality of biological capital in agriculture. However, the success of genes that confer resistance to pests induces a co-evolutionary response that depreciates the biological capital embodied in the crop, as pests evolve the capacity to overcome the crop's new defences. Thus, simply maintaining this biological capital, and the beneficial production and economic outcomes it bestows, requires continual reinvestment in new crop defences. Here we use observed and modelled data on stripe rust occurrence to gauge changes in the geographic spread of the disease over recent decades. We document a significant increase in the spread of stripe rust since 1960, with 88% of the world's wheat production now susceptible to infection. Using a probabilistic Monte Carlo simulation model we estimate that 5.47 million tonnes of wheat are lost to the pathogen each year, equivalent to a loss of US$979 million per year. Comparing the cost of developing stripe-rust-resistant varieties of wheat with the cost of stripe-rust-induced yield losses, we estimate that a sustained annual research investment of at least US$32 million into stripe rust resistance is economically justified.
We thank R. Singh for technical guidance. In addition, attendees of the Borlaug Global Rust Initiative (BGRI) meetings at New Delhi (August 2013) and Obregon, Mexico (March 2014) and the Second International Wheat Stripe Rust Symposium at Izmir, Turkey (April 2014) provided valuable comments and feedback. A substantial portion of the funding was provided by the Wheat CRP by way of the International Maize and Wheat Improvement Center (CIMMYT) with additional support from the University of Minnesota's MnDRIVE Global Food Ventures Initiative and the International Science and Technology Practice and Policy (InSTePP) Center. R.F.P. and W.C. received support from the Australian Grains Research and Development Corporation.