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.

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Identification and selection of plant genotypes with survival, recovery and sustainable performance during drought periods is one of the main objectives of plant improvement for arid and semi-arid regions. This study aimed to evaluate root traits and recovery of tall fescue genotypes after a period of drought stress. A total of twenty four tall fescue genotypes were selected from a wide polycross population and assessed for field drought tolerance based on stress tolerance index (STI) and recovery during 2010-2013. The genotypes were classified as tolerant, moderately tolerant and susceptible based on STI. Then, in 2014, genotypes were assessed in a pot experiment for root characteristics under two levels of moisture environments (control and intense drought stress). In both moisture environments, root length (RL), root area (RA), root volume (RV) and root weight (RW) were negatively correlated with days to recovery (DR). Genotypes that recovered from drought had greater RL, RA, RV and RW than the genotypes unable to recover. Principle component analysis (PCA) was performed to identify genotypes with superior root characteristics, stress tolerance and recovery potential that can be used for future breeding programmes. Results indicated that selection based on combining STI, recovery and extensive root system might improve drought tolerance of tall fescue.

The genetic basis of post-drought recovery, summer dormancy and persistence under drought stress is little investigated in orchardgrass (Dactylis glomerata L.). In this study, polycross populations (half-sib genotypes) were evaluated under normal and regulated deficit irrigation for 3 years (2012–14) in the field. Irrigation was then withheld in 2015, and the genotypes were evaluated for post-drought recovery and persistence. The results showed that regulated deficit irrigation decreased forage yield, yield components, persistence and recovery. A broad range of general combining ability was observed for most of the measured traits. Moderate to high estimation of narrow-sense heritability for yield components, persistence, recovery and summer dormancy index indicated that phenotypic selection may be successful to attain genetic progress. Under deficit irrigation, flowering time was positively correlated with persistence and recovery, indicating that selection based on lateness would lead to improvement in these traits. Stable and superior families across environments were identified based on regression coefficients and principle component analysis that would be desirable in future breeding programs.

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Drought stress has an adverse effect on crop production and food quality. Milk thistle (Silybum marianum L.) is an oil and medicinal crop known as an alternative oil crop with high level of unsaturated fatty acids, which makes it a favourable edible oil for use in food production. Silymarin (a mixture of flavonolignans) is the main active medicinal component. Biochemical diversity, changes induced by water deficit stress in secondary metabolites, and their relationships with production traits in native germplasm are poorly understood in milk thistle. Twenty-six ecotypes mainly collected from different regions of Iran were evaluated for oil, fatty acid profile, triacylglycerol (TAG) composition, silymarin and agro-morphological traits under non-stress and water stress conditions for 2 years. Water stress increased oil and silymarin content while decreasing fruit yield and related traits. The most abundant fatty acid averaged over all ecotypes under both moisture conditions was linoleic acid (L, 39%), followed by oleic acid (O, 36%), palmitic acid (P, 9%) and stearic acid (E, 6%). Among the 24 detected TAGs, the five major compositions were OOL, OLL + OOLn (linolenic), POL, OOO, LLL + OLLn and EOL. Superior ecotypes rich in monounsaturated and polyunsaturated fatty acids were identified and can be introduced as candidates for food, medicinal and industrial purposes. Associations among different attributes are discussed.

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