Interactive effects of root diseases and drought on water use efficiency of wheat

A pot experiment was conducted to investigate the effects of fungal root diseases ('Pythium' and 'Rhizoctonia') and drought at either tillering or anthesis on the water-use efficiency (WUE), water relations, yield components and percentage of root lesion of two Australian bread-wheat cultivars (Mulgara and Janz). There were no significant differences between two pathogens. WUE did not differ between well-watered plants and those droughted at tillering but it was significantly reduced by drought at anthesis. Mulgara had slightly higher WUE than Janz. Drought at both growth stages significantly altered water relations for both cultivars. Uninfected plants of Janz droughted at tillering had higher total water potential (Ψ) and osmotic potential (π) than diseased plants. However, osmotic potential of droughted controls was lower than diseased plants at anthesis. The number of heads, grain weight and grain number were significantly higher for well-watered than droughted plants and higher for Mulgara than Janz. The controls (38%) had significantly less lesioned roots than 'Pythium' (53%) and 'Rhizoctonia' (50%) and root lesion percentage in Janz was significantly higher than Mulgara except in the 'Rhizoctonia' treatment. In conclusion, the pathogens affected water use during tillering but not at later stages when roots developed beyond the inoculation point.