Abstract:

QTLs for salt tolerance (ST) related traits including score of salt toxicity of leaves (SST), survival days of seedlings (SDS), shoot K⁺ concentration (SKC) and shoot Na⁺ concentration (SNC) were detected using the reciprocal introgression lines (ILs) derived from a cross between japonica variety “Lemont” and indica variety “Teqing” under salt stress treatment with the concentration of 140 mmol L^-1 NaCL in green house and phytotron. Both genetic backgrounds of the two sets of ILs were similar to their respective parents. On the average, Lemont genome accounted for 83.8% in Lemont background-ILs whereas 88.9% of Teqing genome in Teqing background-ILs. Continuous variation and transgressive segregation for all ST-related traits were observed in the two IL populations with overlaps of frequency distributions for most traits, suggesting the gene effect of reciprocal introgression of the two parents on each ST-related trait was almost equivalent. Eighteen QTLs for all ST-related traits were identified for each of the two IL populations. No any a common QTL for the same trait was detected in the reciprocal IL populations, indicating there was a strong genetic background effect on expression of ST-QTLs, and also suggesting these ST-QTLs had relatively small phenotypic effect. Only one common QTL affecting SKC was identified in Teqing background-ILs under green house and phototron environments, indicating there was a strong interaction of ST-QTL with environment. Although the two parents are moderately susceptible to salt stress, QTL mapping results indicated that some favorable alleles beneficial to improvement of ST-related traits do exist in the parents. Therefore, it is possible to develop a new variety with improved ST by identifying and mining this kind of “hidden” ST-genes existed in the modern varieties through molecular marker technology and further pyramiding these non-allelic alleles via marker-assisted selection.

Key words: Rice, Salt-tolerant QTL, Genetic background, Gene mining, Marker-assisted selection