Abstract
Soil salt-alkalization is a major limiting factor for crop production in many regions. Switchgrass (Panicum virgatum L.) is a warm-season C4 perennial rhizomatous bunchgrass and a target lignocellulosic biofuel species. The objective of this study was to evaluate relative alkali-salt tolerance among 30 switchgrass lines. Tillers of each switchgrass line were transplanted into pots filled with fine sand. Two months after transplanting, plants at E5 developmental stage were grown in either half strength Hoagland’s nutrient solution with 0 mM Na+ (control) or half strength Hoagland’s nutrient solution with 150 mM Na+ and pH of 9.5 (alkali-salt stress treatment) for 20 d. Alkali-salt stress damaged cell membranes [higher electrolyte leakage (EL) ], reduced leaf relative water content (RWC), net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr). An alkali-salt stress tolerance trait index (ASTTI) for each parameter was calculated based on the ratio of the value under alkali-salt stress and the value under non-stress conditions for each parameter of each line. Relative alkali-salt tolerance was determined based on principal components analysis and cluster analysis of the physiological parameters and their ASTTI values. Significant differences in alkali-salt stress tolerance were found among the 30 lines. Lowland lines TEM-SEC, Alamo, TEM-SLC and Kanlow were classified as alkali-salt tolerant. In contrast, three lowland lines (AM-314/MS-155, BN-13645-64) and two upland lines (Caddo and Blackwell-1) were classified as alkali-salt sensitive. The results suggest wide variations exist in alkali-salt stress tolerance among the 30 switchgrass lines. The approach of using a combination of principal components and cluster analysis of the physiological parameters and related ASTTI is feasible for evaluating alkali-salt tolerance in switchgrass.
Highlights
Salt-alkalization is a major global environmental and land resource issue
The alkali-salt tolerant and sensitive lines were clearly identified based on the physiological parameters by cluster analysis and principal component analysis
The results of this study showed that the information from the five physiological parameters is mainly composed of the three principal components, with cumulative contribution rates accounting for 95.5% of the total genetic variance
Summary
Salt-alkalization is a major global environmental and land resource issue. There is approximately 0.25 to 0.5 Mha of agricultural land lost annually due to soil salinization worldwide, especially in arid and semiarid areas [1]. Switchgrass is a warm-season C4 perennial steppe plant which is native to North America (Great Plains and much of the eastern part) It distributes naturally from 55°N latitude in Canada into the United States and Mexico [7,8,9]. Because switchgrass requires relatively modest levels of fertilizers [11,12,13,14], it can grow on marginal lands, including millions of hectares of salinized lands, to avoid competition with arable lands. This grass can be used for soil conservation because of its strong root system [15]. Selection of switchgrass lines with improved tolerance to alkali-salt stress has been one of the major goals of switchgrass breeding programs
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