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Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/22/2004 Publication Date: 2/10/2005 Citation: Zeng, L. 2005. Exploration of relationship between physiological parameters and growth performance of rice (Oryza sativa L.) seedlings under salinity stress using multivariate analysis. Plant and Soil Journal. 268:51-59. Interpretive Summary: A method for the characterization of salt tolerant rice germplasm is described. The procedure is based on the assumption that resistance to salt stress in rice is strongly associated with the mechanism that plants selectively accumulate and transport both calcium (Ca) and potassium (K) in preference to sodium (Na) in order to prevent Na from being transported to the leaves. In this trial, seedlings from thirty-one different rice types were grown in a greenhouse under saline conditions for about one month. Seedlings of the 31 genotypes were then harvested and analyzed for mineral ion concentrations and growth performance such as tiller number, shoot dry weight, plant height, and leaf area. Genotypes fell into three types. The first type of rice genotypes with good growth performance were efficient in excluding Na from the shoots and tended to accumulate K in preference to Na, whereas, in contrast, the second type of genotypes with poor growth performance contained relatively more Na and less K in their shoots. The third type contained intermediate Na and K compared with the first and second types of genotypes. Interestingly, growth performance among the third genotypes did not match their Na and K contents as closely as in the first and second categories. The inconsistency between ion exclusion and growth performance in the third genotypic category indicates the existence of multiple mechanisms controlling salt resistance in rice. This technique will prove useful for breeders and geneticists for selecting those genotypes that show promise for inclusion in breeding programs aimed at improving the salt tolerance of rice. Technical Abstract: Rice germplasm needs to be classified to quantify genotypic differences for salt tolerance at seedling stages. The goal of this study was to classify a subset of rice germplasm for ion contents and ion selectivity in seedlings by cluster analysis. Plants of thirty-one genotypes were grown under a greenhouse. Two salinity treatments were imposed at 0.9 dS/m (control) and 6.4 dS/m with sodium chloride and calcium chloride (6:1 molar ratio). Seedlings were sampled 34 days after planting. The characters of Na, K, Ca, K-Na selectivity and Na-Ca selectivity were measured as physiological parameters. The characters of tiller number, leaf area, plant height and shoot dry weight were measured as growth parameters. Genotypes grouped into four clusters based on ion contents and ion selectivity using Ward's minimum-variance cluster analysis. K-Na selectivity and shoot Na content contributed the most to the cluster formation. Clusters were ranked based on cluster means of K-Na selectivity and Na content. Genotypes were classified into three categories based on ion cluster rankings: Category 1 with high selectivity and low shoot Na content; Category 2 with intermediate selectivity and shoot Na content; Category 3 with low selectivity and high shoot Na content. The classification of the genotypes into Categories 1 and 3 based on their high or low selectivity was consistent with their growth performance under salt stress. It was concluded that ion selectivity was a relatively dominant mechanism controlling salt tolerance among rice genotypes although multiple mechanisms may be involved under moderate salt stress. The results also provide the first example of the effectiveness of cluster analysis for physiological responses to salinity stress. |
