Abstract:

Knowledge of the genetics of salt tolerance and mining of favorable alleles from germplasm should help develop rice varieties with high salt tolerance. QTLs affecting six salt-tolerance related traits including score of salt toxicity (SST), survival days of seedlings (SDS), shoot K⁺ concentration (SKC), shoot Na⁺ concentration (SNC), root K⁺ concentration (RKC), root Na⁺ concentration (RNC) were detected using 85 backcrossing introgression lines derived from a indica cultivar IR64 and a japonica upland cultivar Tarom molaii from Iran under salt stress with the concentration of 140 mmol L^-1 NaCl at the seedling stage. Continuous variation and transgression for all six traits were observed in the BIL population although there were only significant differences in SDS and SNC between the parents. Correlation analysis indicated that SDS had highly negative correlation with SNC and positive correlation with SKC but no correlations with RKC and RNC, suggesting that salt toxicity of leaves resulted from over-accumulation of Na⁺ in shoots. RKC highly positively correlated with RNC while both of them had no correlations with SKC and SNC, respectively, indicating different mechanisms in uptake of K⁺ and Na⁺ in roots and their transport from roots to shoots. Twenty-three QTLs for the six traits on the ten chromosomes except chromosomes 5 and 10 were identified by single-marker ANOVA using SAS PROC GLM, including 5 for SST, 6 for SDS, 4 for SKC, 4 for SNC, 1 for RKC, and 3 for RNC. Among them, the region of RM240-RM112 on chromosome 2 simultaneously affected SST, SDS, SKC, and SNC and the allele associated with improvement of salt tolerance was from Tarom molaii. This QTL could be useful for improvement of salt tolerance through marker assisted selection. The QTLs affecting SKC and SNC didn’t share the same genomic region with the QTLs for RKC and RNC, further confirming the view that different genetic mechanisms involved in uptake of K⁺ and Na⁺ between roots and shoots. By comparative mapping, 12 (52.2%) QTLs for the six related traits located in the same or near genome regions on chromosomes 1, 2, 3, 7, and 9 with the QTLs previously identified in different mapping populations. The advantages of mapping QTLs using BILs and strategy of mining ‘hidden’ salt-tolerant main-effect QTL from rice germplasm were discussed.

Key words: Rice, Salt-tolerance, Backcrossing introgression lines, Gene mining