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Research on crop response to deficit irrigation is important to reduce agricultural water use in areas where water is a limited resource. The objective of this study was to evaluate changes in physiological and root traits under mild and intense drought stress in tall fescue. It also sought to find associations between these changes and field drought tolerance. A total of 24 tall fescue genotypes were selected from a wide polycross population and assessed for field drought tolerance during 2011-2012 in the field. The genotypes were classified as tolerant, moderately tolerant, and susceptible based on drought stress tolerance index (STI), tolerance index (TOL), and yield reduction (YR). In 2013, 24 genotypes were clonally propagated and planted in polyvinylchloride (PVC) tubes under, three levels of moisture regimes. Root characteristics were investigated at 0-30 and 30-60 cm depths of soil. Also 11 physiological traits, dry forage yield, STI, TOL, and YR were recorded. At the 30-60 cm depths of soil, the root length increased by 5.95 and 7.30 % under mild and intense stress, respectively. Under mild stress, root area and root volume were positively correlated with STI. Consequences of drought stress, manifested as declined relative water content and chlorophyll, could be associated with a decrease in the activity of antioxidant enzymes. Some tall fescue genotypes had extensive root systems, high photosynthetic capacity, and less YR in the field. These genotypes may adapt to drought through drought avoidance and drought tolerance mechanisms. The application of principle component analysis for screening suitable genotypes was also discussed.

Knowledge aboutbiomass partitioning of maize grown in arid and semi-arid climatesis scarceand yet essential to select a robust and effective deficit irrigation management (DIM) strategy for these regions.The objectives of this study were to: i)investigate the effects of different levels of water application under two DIM strategies on the root and aboveground characteristics, the response factor to water stress (K y) and irrigation water use efficiency (IWUE) of silage maize at different growth stages, andii) determine the best DIM strategythat 44 would maximize biomass productivity.Field pot experimentswere conducted in Isfahan, 45 Iran,during 2009 and 2010.The twoDIM strategies werefixed irrigation interval-variable 46 irrigation depth (M 1), and variable irrigation interval-fixed irrigation depth (M 2).Each DIM strategy was tested at four water-deficit levels, including: severe, moderate, mild,and a fullirrigation.In M 1 , irrigation intervals were consistent for all irrigation treatmentsbut were varied over the growing season. Treatment effects weremeasured at the10-leaf, 16-leaf, tasseling, milk,and silage harvestcrop growth stages.There was significant effect of irrigation and growth stage on total aboveground biomass (TB), leaf area (LA), root biomass (RB), and root:shoot ratio (RSR)for both DIM strategies during the two years.For M 2 , there was 53 significant difference in TB, LA, RB, and RSR between all irrigation levels at all growth 54 stages.TB production was on the average around 25% higher for M 1 compared to M 2 , even 55 though total applied irrigation water was only 6% higher for M 1 .Comparing the two DIMsshowed that RSR and K y wereboth higherforM 2 , indicating that the crop was more sensitive to this strategy.In conclusion, M 1 was selected as the best management practicesince it had more favorable effects on improving the IWUE and also on the development of maize rootsduring the growing season.

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