*4.10. Light Microscope Observation of P. viticola Zoospore Release from Zoosporangia and Zoospore Germination*

A zoosporangium suspension of *P. viticola* (1 × 104 zoosporangia/mL) was prepared as mentioned above. Nine hundred microliters of the zoosporangium suspension was incubated with 100 <sup>μ</sup>L of KOF112 solution (1 × <sup>10</sup><sup>8</sup> cfu/mL, containing 10% SCD), 10% SCD medium, or *Agrobacterium* sp. isolate CHB3 (1 × 108 cfu/mL, containing 10% SCD) in a microtube at 22 ◦C for 1 h under light irradiation (11.8 Wm<sup>−</sup>2), and then for 23 h in the dark. Zoospore release from zoosporangia was observed under a light microscope (Olympus BX51, Tokyo, Japan). Zoospore release rate was calculated using the following formula:

zoospore release (%) = number of empty zoosporangia/number of total zoosporangia × 100

Zoospore germination was counted as described previously, with minor modifications [6]. Briefly, a zoosporangium suspension of *P. viticola* (1 × 104 zoosporangia/mL) was prepared as mentioned above. Five hundred microliters of the zoosporangium suspension was incubated in a microtube at 30 ◦C for 4 h under light irradiation (11.8 Wm−2). One hundred microliters of KOF112 solution (1 × 108 cfu/mL, containing 10% SCD), 10% SCD, or *Agrobacterium* sp. isolate CHB3 (1 × <sup>10</sup><sup>8</sup> cfu/mL, containing 10% SCD) was added into the microtube, and then incubation was carried out at 30 ◦C for 12 h under light irradiation (11.8 Wm−2), followed by incubation at 30 ◦C for 8 h in the dark. The suspension was stained with 0.05% aniline blue in 0.0067M K2HPO4 (pH 9–9.5) at room temperature for 20 min. Zoospore germination was observed using a fluorescence microscope (Olympus BX51). Zoospore germination rate was calculated using the following formula:

germination (%) = number of germinated zoospores/number of total zoospores × 100
