Tolerant crops increase growers’ yields but promote selfishness: how the epidemiology of disease resistant and tolerant varieties affect grower behaviour

Abstract

1SummaryDisease management often involves genetically improved crops. Resistant varieties are less susceptible, and so less likely to act as reservoirs of inoculum. Tolerant varieties can be highly susceptible, but limit yield loss for those who grow them. Population-scale effects of deploying resistant or tolerant varieties have received little consideration from epidemiologists.We examined how tolerant and resistant crop have opposing consequences upon the uptake of control using a behavioural model based on strategic-adaptive expectations. Growers compared last season’s profit with an estimate of what could be expected from the alternative crop type, thereby assessing whether to alter their strategy for the next season.Tolerant crop only benefited growers using it, decreasing yields for others. This incentivises widespread use via a negative feedback loop. Resistant crop was more widely beneficial, with reduced population-scale disease pressure leading to increased yields for all. However, this positive externality allows growers who do not deploy resistant crop to “free-ride” upon the management of others.This work highlights how a community of growers responds to the contrasting incentives caused by tolerant and resistant crop varieties, and how this leads to very distinct effects on yields and population-scale deployment.