Effect of zoospore-free fluid (ZFF) on aggregation of Phytophthora nicotianae and Phytophthora sojae zoospores. Zoospores of P. nicotianae (2 × 103 ml-1) were incubated in ZFF of (A) Py. aphanidermatum, (B) P. capsici, (C) P. sojae, and (D) sterile distilled water (SDW). Zoospores of P. sojae (2 × 103 ml-1) were incubated in ZFF of (E) Py. aphanidermatum, (F) P. capsici, (G) P. nicotianae and (H) SDW. Images were captured 18 hours after incubation at 23°C. Bar = 50 μm.