Quantitative Trait Loci for Component Physiological Traits Determining Salt Tolerance in Rice

Abstract

Rice (Oryza sativa) is sensitive to salinity, which affects one-fifth of irrigated land worldwide. Reducing sodium and chloride uptake into rice while maintaining potassium uptake are characteristics that would aid growth under saline conditions. We describe genetic determinants of the net quantity of ions transported to the shoot, clearly distinguishing between quantitative trait loci (QTL) for the quantity of ions in a shoot and for those that affect the concentration of an ion in the shoot. The latter coincide with QTL for vegetative growth (vigor) and their interpretation is therefore ambiguous. We distinguished those QTL that are independent of vigor and thus directly indicate quantitative variation in the underlying mechanisms of ion uptake. These QTL independently govern sodium uptake, potassium uptake, and sodium:potassium selectivity. The QTL for sodium and potassium uptake are on different linkage groups (chromosomes). This is consistent with the independent inheritance of sodium and potassium uptake in the mapping population and with the mechanistically different uptake pathways for sodium and potassium in rice under saline conditions (apoplastic leakage and membrane transport, respectively). We report the chromosomal location of ion transport and selectivity traits that are compatible with agronomic needs and we indicate markers to assist selection in a breeding program. Based upon knowledge of the underlying mechanisms of ion uptake in rice, we argue that QTL for sodium transport are likely to act through the control of root development, whereas QTL for potassium uptake are likely to act through the structure or regulation of membrane-sited transport components.

Screening, Inheritance and Linkage Marker Analyses of Salt Tolerance in Mutated Scented Japonica Rice (Oryza sativaL.)

“…These results indicate that the salt-tolerance of SM61 was governed by a single dominant gene. These results differ from those obtained in some traditional indica salt-tolerant varieties, such as Pokkali, Nona Bokra, and Kararata, in which inheritance of salt-tolerance is known to be governed by polygenes (Zhang et al, 1995;Lin et al, 1998;Gong et al, 1999;Prasad et al, 2000;Koyama et al, 2001;Lin et al, 2004). This is the fi rst report that in F 1 and F 2 salt-tolerant rice plants, the salt-tolerance is governed by a single dominant gene.…”

“…Thirtyone F 3 lines derived from the F 2 salt-tolerant plants were used to evaluate the genotypes of F 2 plants. We found that the SM61 mutated salt-tolerance gene, ST8, is located on chromosome 8, different from those previous QTL regions previously discovered on chromosome 1, 3, 4, 5, 6, 7, 9, 10 and 12 (Zhang et al, 1995;Lin et al, 1998;Gong et al, 1999;Prasad et al, 2000;Koyama et al, 2001;Lin et al, 2004;Ren et al, 2005;Lee et al, 2007;Sabouri and Sabouri, 2008). By applying MAS techniques to the gene we have identified as responsible for conferring salttolerance, the results of our study could be used to improve salt tolerance of japonica scented rice.…”

“…Zhang et al (1995), Lin et al (1998), Gong et al (1999) and Prasad et al (2000) found QTLs involved in salt tolerance of rice on chromosome 7, 5, 1 and 6. Ten QTLs for Na + and K + uptake, Na + and K + concentration, and Na + /K + ratio in the shoot have been identifi ed (Koyama et al, 2001). Lin et al (2004) detected eleven QTLs that define the survival period of seedlings, as well as the traits of the shoots and roots in relation to salt tolerance in rice under salt stress on chromosomes 1, 4, 6, 7 and 9.…”

“…Sabouri and Sabouri (2008) found nine QTLs for chlorophyll content, root length, root dry weight and ion exchange on chromosomes 1, 3, 4, 7, 9 and 10, which increased salt tolerance at the seedling stage. Most QTLs related to salt-tolerance were located in a similar region on chromosome 1 (Gong et al, 1999;Koyama et al, 2001;Lin et al, 2004;Ren et al, 2005). Identification of new QTLs related to salt tolerance through marker-assisted selection (MAS) should be useful in rice breeding programs (Kaushik et al, 2003;Lin et al, 2004;Lee et al, 2007).…”

“…QTL map studies on salttolerance provide information towards the improvement of plant breeding under saline conditions. In previous studies (Zhang et al, 1995;Lin et al, 1998;Gong et al, 1999;Prasad et al, 2000;Koyama et al, 2001;Lin et al, 2004;Ren et al, 2005;Lee et al, 2007;Sabouri and Sabouri, 2008), the location of QTLs for salt tolerance in rice was examined by using molecular markers. Zhang et al (1995), Lin et al (1998), Gong et al (1999) and Prasad et al (2000) found QTLs involved in salt tolerance of rice on chromosome 7, 5, 1 and 6.…”