Drought effect on growth, gas exchange and yield, in two strains of local barley Ardhaoui, under water deficit conditions in southern Tunisia
Highlights
► Barley is the main cereal grown in the south of Tunisia. ► The crop is well adapted to arid environment. ► Yield of barley was reported to reduce when it is waterlogged during its early stage. ► Drought stress affects many traits through morphological and physiological modifications. ► We selected the most drought-tolerant plant material in conditions of water stress.
Introduction
Among the abiotic stresses, drought is by far the most complex and devastating on a global scale (Ceccarelli, 2010; Pennisi, 2008) and its frequency is expected to increase as a consequence of climate changes (Ceccarelli et al., 2010). Cultivating plants with increased stress resistance appears critical to maintain yield stability. Barley is the main cereal grown in these areas, because it shows a conservative strategy in water use when compared to other species (Acevedo, 1987). The crop is well adapted to semi-arid environment although its yield has been severely hindered by water deficit and aeration stress (Araya and Stroosnijder, 2010). In this sense, barley yield was reported to reduce when it is waterlogged even for few hours during its early stage between 2 and 6 weeks after planting (Setter and Waters, 2003). Drought stress affects simultaneously many traits through morphological, physiological, and metabolic modifications occurring in all plant organs, finally leading to decreased grain yield (Sacks et al., 1997; Cellier et al., 1998; Cochard et al., 2002). Drought stress during the grain-filling period decreased the net photosynthetic rate of the flag leaf of barley, but had no significant effect on the grain-filling rate under high vapour pressure deficit (Sánchez-Díaz et al., 2002). Middle to late drought stress advanced leaf senescence, shortened the grain-filling period and decreased grain yield and individual grain weight of barley (González et al., 1999; Jamieson et al., 1995; Sánchez-Díaz et al., 2002; Voltas et al., 1999). Growth is generally more sensitive to water-deficits than gas exchange, and reductions in growth may occur at moderate soil water-deficits, even if plant relative water content does not change significantly (Passioura, 1988; Kuang et al., 1990; Gowing et al., 1990; Pereira and Chaves, 1993; Keya, 1998). To select adapted plant material to Mediterranean-type climates, it is necessary to consider phenological, agronomic, morphological and physiological parameters (González et al., 1999; González and Ayerbe, 2009) in order to improve crop adaptation to drought. The development of well-adapted crops might improve yields under these conditions as observed in barley (Gonzalez et al., 2007). Instantaneous water use efficiency (WUEinstantaneous), which is the ratio between the net photosynthesis and transpiration, could be considered as a short-term measurement of water use efficiency (Ehleringer, 1993). Relative changes of (WUEinstantaneous) under stress compared to control conditions may also show the degree of stress tolerance of the plants. The knowledge of the mechanisms that regulate barley photosynthesis under different water regimes is of great interest to understand the key factors that regulate plant water use efficiency and barley yield. In the present work, we compared the behaviour of two strains of a local barley (Hordeum vulgare L.) cultivar Ardhaoui (unique cultivar of southern Tunisia) in conditions of water stress in order to select the most drought-tolerant plant material through parameters measured at the leaf (plant water status and gas exchange) and plant (growth and yield) levels, then we investigated morpho-physiological criteria for evaluating drought tolerance in studied barley strains.
Section snippets
Plant material and location
The experiment was conducted in a glasshouse located 20 km south-east Medenine at the Institute of Arid Regions. The climate is Mediterranean, with hot, dry summers and mild winters. Barley is a typical crop of marginal areas in North Africa. Most farmers in the marginal areas use their own varieties of barley (landraces). A landrace has been defined by Zeven (1998) as an autochthonous variety with a high capacity to tolerate biotic and abiotic stress, resulting in a high yield-stability and an
Leaf growth parameters and leaf RWC
The leaf RWC in well-watered plants ranged from 89 to 91 % and the LA was highest in Switir (8 cm2) (Table 1). LA and RWC were found to be positively correlated under well watered conditions (r = 0.76). LA was higher in control plants than the water stressed ones. LA, in general, was higher under favourable conditions than under water deficit conditions (Table 1). Under well watered conditions, LAR was higher in Tlalit (3 leaf day−1 plant−1) than Switir (2 leaf day −1 plant −1) (Table 1). A
Leaf growth parameters and leaf RWC
Under water deficit stress, leaf area was sharply reduced due a combination of leaf growth reduction and abscission. Tlalit strain, with the highest decline in leaf area under stress also showed the highest decline in leaf appearance rate (Table 1). A positive and highly significant relationship was found between RWC and LA (r = 0.980; P < 0.01; Table 3). Reduced expansion of younger leaves caused a decrease in the LAR in stressed plants. The responses of LA to water stress show much genotypic
Conclusions
In conclusion, our results indicate that water deficit stress restricted growth of Switir and Tlalit strains independently of their origins. However, Tlalit strain was more tolerant to water deficit than Switir, as shown by their relatively lower RWC reduction under water deficit conditions. The higher tolerance of Tlalit populations to water shortage may be related to their stomatal control of gas exchange. Drought tolerance of Tlalit was found to be associated with a higher reduction in LA
Acknowledgements
The authors are grateful to the group of Prof. William Payne (Texas A&M University), especially to Linda Sturm-Flores, for the critical reading of the manuscript and help with the English language.
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