Motility and chemotactic response of Phytophthora cinnamomi zoospores in ‘ideal soils’

Abstract

Columns 21 and 50 × 1.8 cm filled with cleaned, glass microbeads of graded sizes were used to study the effects of transport and mobility in bulk flow situations and also of static confinement on motility and chemotaxis of zoospores of Phytophthora cinnamomi Rands suspended in 1 mM-NaCl. Passage at 2.5 cm/min through 21 cm columns caused little loss of motility even with beads providing pore necks with a diameter (25–35 μm) slightly less than the overall dimension of a zoospore with extended flagella. Likewise there was little effect on motility even when zoospores were passed at 50 cm/min, 70 times autonomous swimming speed, through beads with necks 230–300 or 150–200 μm, the latter being equivalent to the wavelength of the helical pathway of a free-swimming zoospore. Zoospores failed to pass through columns of beads with pore necks 5–10 μm, i.e. less than the dimensions of the zoospore soma (6 × 15 μm). Static confinement in columns of glass beads with pore necks 25–35 or 150–200 μm had almost no effect on encystment over the first hour; by the end of 6 h it had hastened natural encystment by approximately 10%. Contact stimulus is thus unimportant in contrast to results reported for some other species of Phytophthora. Where pore neck size was large enough to have allowed unimpeded movement along helical pathways, chemotaxis to 5 mm ethanol in Pfeffer tubes inserted into ports on 50 cm horizontal columns was slight if zoospores were moved passively at greater than their swimming speed, but increased at slower speeds and was 7.5 times that of the control when there was no flow.