Figure 2. Swimming trajectories of P. parasitica zoospores.

(A) Trajectories of zoospores swimming in water captured from the microscopic assay for 60 s. Sample size $N=58$. Note: not all trajectories are shown. Each position of the zoospores is captured every $\mathrm{\Delta }t=0.0167\mathrm{s}$. The trajectories are smoothed with moving average (step length $n=12$). (B) The progression of speed $U$ and (C) moving directions θ over time of a single zoospore extracted from the population in the assay. (D) Distribution of zoospore speed $p(U)$. (E) Polarity distribution of moving direction $p(\theta )$. (F) Survival curves $p(\tau \ge t)$ of the running time ${\tau }_{\mathrm{r}}$ and stopping time ${\tau }_{\mathrm{s}}$. (G) Distribution of turning angle $p(\mathrm{\Delta }\theta )$, with positive angle values indicating counter-clockwise, and negative as clockwise direction. (H) Schematics showing the strategy of the simulation model of zoospores swimming in water. (I) The estimated mean squared displacement (MSD) over time intervals $t$, constructed from the simulation data. The inset compares the experimental data and simulation of MSD at the experimental time-scale of 60 s. By simulation, at long time scale of 1 h, MSD of zoospores shows a diffusion of Brownian particles with the diffusion coefficient $D=3.5\times {10}^{-4}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$.