Sclerophylly and leaf anatomical traits of five field-grown olive cultivars growing under drought conditions.
Some ecologically different ecotypes of Panicum antidotale Retz. were evaluated for drought tolerance in relation to growth parameters and leaf structural modifications. These ecotypes were adapted to normal non-stressed (agricultural field AF, and sludge of disposal channel SDC), drought-stressed (along roadside AR), salinity-stressed (forest plantation FP), waterlogging and salinity-stressed (inside disposal channel IDC), and drought plus salinity-stressed (barren area BA). On the basis of genetic variability in leaf structural modifications, each ecotype adopted specific strategies to tolerate the extremity of drought stress. The AF and SDC ecotypes relied on water conservation and survival rather than growth and structural modifications by developing epidermis and sclerenchyma on both leaf surfaces. The AR developed xerophytic foliar characteristics in addition to maintaining growth and development under stressed conditions like thick leaves, well-developed bulliform cells, and intensive sclerification. The FP ecotype developed efficient strategy for drought tolerance such as reduced and fibrous leaves, smaller metaxylem vessels, and highly developed bulliform cells. The ecotype IDC relied more on water conservation by increasing leaf epidermal thickness and decreasing stomatal area and density. The ecotype BA showed critical structural adaptations such as thin leaves, extremely developed bulliform and reduced metaxylem area, and parenchyma extensions above vascular bundles. Based on the strategies adopted for drought tolerance, the tolerance level of these ecotypes were rated as BA > AR > FP > IDC > SDC > AF.