THE HYDRAULIC CONDUCTIVITY OF ROOTS OF RUST-INFECTED BARLEY SEEDLINGS

The influence of Puccinia hordei (rust) infection on the root hydraulic conductivity (Lp) of excised roots of Hordeum distichum cv. Maris Mink (barley) was investigated using the Scholander pressure chamber technique. The solute potential of the root exudate was also measured to determine the contribution of the osmotic component to the total driving force for water flow across the roots. The root Lp of infected plants was significantly lower than control plants on days 5, 6 and 7 after infection. On days 4 and 8 after infection, Lp did not differ significantly. Root Lp increased with time for both control and infected plants from days 5 to 8 after infection. Root Lp varied between 1·4 and 3·6 × 10-5 cm s-1 MPa-1 for roots of infected plants, and between 2·3 and 4·0 × 10-5 cm s-1 MPa-1 for control plants. The solute potential of root xylem sap exudate was significantly higher (less negative) than that of control sap on days 6, 7 and 8 after infection, reflecting a decrease in the transport of solutes into the root xylem of roots of diseased plants. In control and infected plants, as the applied pressure increased, solute potential root exudate increased. These results are discussed in relation to the known susceptibility of rust infected plants to drought and the mechanisms by which rust infection increases such susceptibility. © 1991 Academic Press Limited.