Rich dynamics of a simple delay host-pathogen model of cell-to-cell infection for plant virus

Viral dynamics within plant hosts can be important for under- standing plant disease prevalence and impacts. However, few mathematical modeling efforts aim to characterize within-plant viral dynamics. In this pa- per, we derive a simple system of delay differential equations that describes the spread of infection throughout the plant by barley and cereal yellow dwarf viruses via the cell-to-cell mechanism. By incorporating ratio-dependent inci- dence function and logistic growth of the healthy cells, the model can capture a wide range of biologically relevant phenomena via the disease-free, endemic, mutual extinction steady states, and a stable periodic orbit. We show that when the basic reproduction number is less than 1 (R0 < 1), the disease-free steady state is asymptotically stable. When R0 > 1, the dynamics either converge to the endemic equilibrium or enter a periodic orbit. Using a ratio- dependent transformation, we show that if the infection rate is very high rela- tive to the growth rate of healthy cells, then the system collapses to the mutual extinction steady state. Numerical and bifurcation simulations are provided to demonstrate our theoretical results. Finally, we carry out parameter esti- mation using experimental data to characterize the effects of varying nutrients on the dynamics of the system. Our parameter estimates suggest that varying the nutrient supply of nitrogen and phosphorous can alter the dynamics of the infection in plants, specifically reducing the rate of viral production and the rate of infection in certain cases.