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

A spatially explicit, interacting particle system model was developed to si mulate the heterogeneous transmission of viruses in fungal populations. Thi s model is based primarily on hypoviruses in the chestnut blight fungus, Cr yphonectria parasitica, which debilitate their hosts and function as biolog ical control agents. An important characteristic of this system is that vir us transmission occurs freely between individuals in the same genetically d efined vegetative compatibility (vc) type, but is restricted among individu als in different vc types, resulting in heterogeneous transmission. An addi tional source of heterogeneity is spatial structure in host populations; vi ruses are dispersed by fungal spores which disperse relatively short distan ces. The model showed that vc type diversity is highly correlated to the ho rizontal transmission rate and therefore significantly affects virus invasi on. The probability of virus invasion decreased as the diversity of vc type s increased. We also demonstrated that virus transmission would be overesti mated if we assumed virus transmission was homogeneous, ignoring both genet ic and spatial heterogeneity. Genetic and spatial heterogeneity are not ind ependent because both are affected by the reproductive biology of the fungu s. In asexual populations, restricted fungus dispersal resulted in nonrando m spatial patterns of vc types, increasing the chance of contact between ve getatively compatible individuals, and promoting virus transmission. In con trast, virus transmission was poor in sexual populations due to spatial ran domization of vc types by long distance dispersed sexual spores. Finally, t his 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-transg enic strains. Virus invasion was still restricted by vc type diversity in t he resident fungus population. Simulation of inundative releases of transge nic virus-infected strains slightly improved virus establishment, but virus es did not persist after treatment was terminated. (C) 2000 Elsevier Scienc e B.V. All rights reserved.