A spatially-structured stochastic model to simulate heterogenous transmission of viruses in fungal populations

A spatially explicit, interacting particle system model was developed to simulate the heterogeneous transmission of viruses in fungal populations. This model is based primarily on hypoviruses in the chestnut blight fungus, Cryphonectria parasitica, which debilitate their hosts and function as biological control agents. An important characteristic of this system is that virus transmission occurs freely between individuals in the same genetically defined vegetative compatibility (vc) type, but is restricted among individuals in different vc types, resulting in heterogeneous transmission. An additional source of heterogeneity is spatial structure in host populations; viruses are dispersed by fungal spores which disperse relatively short distances. The model showed that vc type diversity is highly correlated to the horizontal transmission rate and therefore significantly affects virus invasion. The probability of virus invasion decreased as the diversity of vc types increased. We also demonstrated that virus transmission would be overestimated if we assumed virus transmission was homogeneous, ignoring both genetic and spatial heterogeneity. Genetic and spatial heterogeneity are not independent because both are affected by the reproductive biology of the fungus. In asexual populations, restricted fungus dispersal resulted in nonrandom spatial patterns of vc types, increasing the chance of contact between vegetatively compatible individuals, and promoting virus transmission. In contrast, virus transmission was poor in sexual populations due to spatial randomization of vc types by long distance dispersed sexual spores. Finally, this model was used to evaluate the release of genetically engineered virus-infected strains for disease management. The release of transgenic strains resulted in only marginally greater virus establishment than for non-transgenic strains. Virus invasion was still restricted by vc type diversity in the resident fungus population. Simulation of inundative releases of transgenic virus-infected strains slightly improved virus establishment, but viruses did not persist after treatment was terminated. (C) 2000 Elsevier Science B.V. All rights reserved.