Salt tolerance evaluation and mini-core collection development in Miscanthus sacchariflorus and M. lutarioriparius

Abstract

Marginal lands, such as those with saline soils, have potential as alternative resources for cultivating dedicated biomass crops used in the production of renewable energy and chemicals. Optimum utilization of marginal lands can not only alleviate the competition for arable land use with primary food crops, but also contribute to bioenergy products and soil improvement. Miscanthus sacchariflorus and M. lutarioriparius are prominent perennial plants suitable for sustainable bioenergy production in saline soils. However, their responses to salt stress remain largely unexplored. In this study, we utilized 318 genotypes of M. sacchariflorus and M. lutarioriparius to assess their salt tolerance levels under 150 mM NaCl using 14 traits, and subsequently established a mini-core elite collection for salt tolerance. Our results revealed substantial variation in salt tolerance among the evaluated genotypes. Salt-tolerant genotypes exhibited significantly lower Na⁺ content, and K⁺ content was positively correlated with Na⁺ content. Interestingly, a few genotypes with higher Na⁺ levels in shoots showed improved shoot growth characteristics. This observation suggests that M. sacchariflorus and M. lutarioriparius adapt to salt stress by regulating ion homeostasis, primarily through enhanced K⁺ uptake, shoot Na⁺ exclusion, and Na⁺ sequestration in shoot vacuoles. To evaluate salt tolerance comprehensively, we developed an assessment value (D value) based on the membership function values of the 14 traits. We identified three highly salt-tolerant, 50 salt-tolerant, 127 moderately salt-tolerant, 117 salt-sensitive, and 21 highly salt-sensitive genotypes at the seedling stage by employing the D value. A mathematical evaluation model for salt tolerance was established for M. sacchariflorus and M. lutarioriparius at the seedling stage. Notably, the mini-core collection containing 64 genotypes developed using the Core Hunter algorithm effectively represented the overall variability of the entire collection. This mini-core collection serves as a valuable gene pool for future in-depth investigations of salt tolerance mechanisms in Miscanthus.

Keywords: Miscanthus lutarioriparius; Miscanthus sacchariflorus; comprehensive evaluation; core collection; ion homeostasis; salt tolerance; seedling stage.

Figure 1

Collection sites of 318 M. sacchariflorus and M. lutarioriparius genotypes (excluding M. × giganteus) from different regions of China.

Figure 2

Determination of the optimal NaCl concentration for evaluating salt tolerance. The NaCl concentration of the salt-injury index (SII) is 0.5 of leaves increased number (NIL) (A), leaf expansion rate (LER) (B) of ten Miscanthus genotypes under different NaCl concentrations, as well as the effect on leaf senescence scale (Sen) (significance of the t-test: ^*** P<0.001) (C). Data in the figure are means of ten Miscanthus genotypes for each trait under each concentration of NaCl.

Figure 3

Plants were subjected to 150 mM NaCl (S) and control (CK) conditions for 0 (left panel) and 17 days (right panel). Each group of two adjacent hydroponic containers, from left to right, was used to represent the CK and S conditions, respectively. The position of each plant in these two hydroponic containers was matched one-to-one.

Figure 4

Na⁺ and K⁺ concentrations and K⁺/Na⁺ ratios in M. sacchariflorus and M. lutarioriparius under 150 mM NaCl. Ion concentrations for 15 genotypes with the highest shoot Na⁺ concentration (SNC) and 15 genotypes with the lowest shoot Na⁺ concentration (A), and ion concentrations for 15 genotypes with the highest root Na⁺ concentration (RNC) and 15 genotypes with the lowest root Na⁺ concentration (B). SK/N and RK/N are K⁺/Na⁺ ratios in shoots and roots, respectively.

Figure 5

Pearson correlation analysis between 14 traits of the entire and core collections. *, **, and *** indicate significance at P<0.05, P<0.01, and P<0.001, respectively. Salt-tolerance index of leaves increased number (RNIL), salt-tolerance index of leaf expansion rate (RLER), leaf senescence scale (Sen), shoot water content (SWC), root water content (RWC), shoot Na⁺ concentration (SNC), root Na⁺ concentration (RNC), the ratio of shoot Na⁺ concentration to root Na⁺ concentration (SN/RN), shoot K⁺ concentration (SKC), root K⁺ concentration (RKC), the ratio of shoot K⁺ concentration to root K⁺ concentration (SK/RK), the ratio of shoot K⁺ concentration to shoot Na⁺ concentration (SK/N), and the ratio of root K⁺ concentration to root Na⁺ concentration (RK/N).

Figure 6

Principal component analysis plot of the entire and mini-core sets of M. sacchariflorus and M. lutarioriparius based on 14 traits. The angles captained by any of the two arrows less than 90° imply the two indices have a positive correlation, otherwise they represent a negative correlation between the two indices. Salt-tolerance index of shoot growth rate (RGR), salt-tolerance index of leaves increased number (RNIL), salt-tolerance index of leaf expansion rate (RLER), leaf senescence scale (Sen), shoot water content (SWC), root water content (RWC), shoot Na⁺ concentration (SNC), root Na⁺ concentration (RNC), the ratio of shoot Na⁺ concentration to root Na⁺ concentration (SN/RN), shoot K⁺ concentration (SKC), root K⁺ concentration (RKC), the ratio of shoot K⁺ concentration to root K⁺ concentration (SK/RK), the ratio of shoot K⁺ concentration to shoot Na⁺ concentration (SK/N), and the ratio of root K⁺ concentration to root Na⁺ concentration (RK/N).

Figure 7

Hierarchical cluster analysis based on the Euclidean distance to evaluate the salt tolerance of 318 M. sacchariflorus and M. lutarioriparius. HST, highly salt tolerant; ST, salt tolerant; MST, moderately salt tolerant; SS, salt sensitive; and HSS, highly salt sensitive.