Speaker
Description
In seasonal agroecosystems, diseases persist through both horizontal transmission during the growing season and vertical transmission via farmer-saved seeds. To break this cycle, growers can purchase and plant disease-free seeds, so called clean seeds. Their choice is then between getting such seeds or reusing cost-free, potentially infected farmer seeds. We investigate the combined dynamics of plant epidemics and grower behavior using a semi-discrete model that couples a metapopulation epidemic framework with game-theoretic imitation dynamics. We show that the equilibrium proportion of growers adopting clean seeds depends critically on the seed-sharing structure, with regimes ranging from polarized bang-bang to mixed strategies as functions of clean seed cost and disease characteristics. When clean seed users do not contribute to the farmer seed pool, small increases in seed price can trigger catastrophic shifts toward widespread infection. Conversely, when seed-sharing creates a common pool, clean seeds provide community-wide disease dilution, initiating a free-riding dilemma: growers may avoid costs while benefiting from the reduced prevalence maintained by others. Finally, we consider not-so-clean seeds, showing that free-riding disappears because of spill-over of the disease they carry to the farmer seed users. When appropriately priced, not-so-clean seeds help stabilize prevalence at manageable levels by balancing the payoff between costly control and epidemic risk.
