Soil Water Extraction, Measured by Computer-Assisted Tomography, in SeedlingLupinus angustifoliuscv. Yandee when Healthy and Infected withPhytophthora cinnamomi

The water-mould fungus Phytophthora cinnamomi Rands causes drought-like symptoms on many hosts, and yet the mechanisms by which infection leads to wilting are not fully understood. This is the first study to describe in detail changes in soil water around the root with infection. Computer-assisted tomography (CAT) was used with Lupinus angustifolius L. cv. Yandee to examine drawdowns (removal of soil water) around a central root infected by P. cinnamomi in a white sand. No growth differences in roots or shoots were found between healthy and diseased plants during the 8 d of the experiment.However, drawdowns failed at high levels of inoculum (8–16 /Pc-infected millet seeds/plant) by 8 d. Water contents in pots with uninfected plants were in the range 0·09–0·12 cm3 water cm−3 soil in the centre of the pot, while water contents in pots with infected plants at 16 millet seeds applied were in the range of 0·16–0·19 cm3 water cm−3 soil in the centre of the pot. A higher transpirational demand produced lower soil water contents near the root but this effect was confounded with infection: disease was more pronounced with higher transpirational demand, and disease led to an increase in water content.