Effect of Root Pruning and Pythium On Water Use Efficiency of Wheat Under Drought.

Roots have a crucial role in water uptake. However, roots can be damaged by root pathogens or mechanical root pruning. A pot experiment was carried out in a glasshouse to compare the effects of root pruning and Pythium irregulare on grain yield and water use efficiency (WUE) of wheat (cv. Janz) under drought conditions. Ten grams of Pythium inoculum (colonized Pythium with millet seeds) were mixed with 4.5 kg soil before sowing. Root pruning was imposed to a depth of 10 cm by inserting a knife into the soil 4 times around each plant at inflorescence emergence stage. Droughting started at the grain filling stage by watering with an amount equivalent to half of the water lost by the treatment with lowest evapotranspiration, so that pots were dried slowly. Watering was stopped completely one week before harvest. Pythium had no effect on transpiration, grain yield and WUE. The transpiration of root pruned plants was less than in controls between the time of root pruning and the start of the drought treatment. Root pruned plants had higher transpiration than controls during the drought. Root pruning treatment significantly decreased total grain weight, grain number, WUE and harvest index. The reduction of grain number for root pruning was greater than for total grain weight. 1000-grain weight was significantly increased by root pruning compared with Pythium but there was no significant difference between root pruning and controls. The ability to make use of the extra water available after anthesis depends on a number of factors including the rate at which soil dries down. The extra water available in the root pruned pots at the end of experiment was not enough to bring the grain yield and WUE up to controls. Root pruning did more than just restrict the ability to access all the water. The experiment showed the importance of the stage at which root damage occurs and how it affects total WUE.