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In arid and semi-arid areas, wheat production is limited by drought mainly at the post-anthesis stage. Root diseases also affect the productivity of wheat. This work reports an examination of the response of wheat plants to the interaction of drought and root diseases. The major hypothesis was that root diseases reduce water use efficiency (WUE) under drought conditions. The preliminary experiment compared two cultivars, two root diseases and drought at two plant growth stages. There were no differences between the two root diseases, 'Pythium' and 'Rhizoctonia', however, there was reduced transpiration in diseased plants of cv. Janz following tillering drought, and of cv. Mulgara following anthesis drought. WUE was not affected by diseases. In experiments with deeper pots and post-anthesis drought treatment, 'Pythium' reduced transpiration prior to anthesis. When plants were regularly rewatered to field capacity before the post-anthesis drought, 'Pythium' had no effect on grain yield and WUE grain. When both infected and control plants were given the same total volume of water at high inoculum densities, infected plants had higher WUE grain than controls. Water uptake by infected roots was reduced during early plant growth due to root damage, but was higher than controls during post-anthesis drought due to higher remaining soil water availability, when compared with non-infected plants. However, diseased plants were not able to access all of the additional water and grain yields were not different from controls. Hydroponic experiments compared the effects of 'Pythium' and root pruning on plant water relations. 'Pythium', polyethyleneglycol-induced drought and root pruning reduced transpiration to a similar extent, but only 'Pythium' reduced shoot dry weight. 'Pythium' had no effect on total or instantaneous WUE. This experiment suggested that the effect of 'Pythium' was more than just in reducing the effective size of the root system. Root pruning at a late stage of vegetative growth in pots reduced WUE, demonstrating the importance of the stage at which root damage occurs on how it affects total WUE. Overall, root diseases did not reduce WUE. Reduction in growth was due to reduced transpiration. This did, however, lead to more water being available in soil during a post-anthesis drought. |
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