Exploring novel genetic sources of salinity tolerance in rice through molecular and physiological characterization.
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BACKGROUND AND AIMS: Agricultural productivity is increasingly being affected by the build-up of salinity in soils and water worldwide. The genetic base of salt-tolerant rice donors being used in breeding is relatively narrow and needs broadening to breed varieties with wider adaptation to salt-affected areas. This study evaluated a large set of rice accessions of diverse origins to identify and characterize novel sources of salt tolerance. METHODS: Diversity analysis was performed on 107 germplasm accessions using a genome-wide set of 376 single-nucleotide polymorphism (SNP) markers, along with characterization of allelic diversity at the major quantitative trait locus Saltol Sixty-nine accessions were further evaluated for physiological traits likely associated with responses to salt stress during the seedling stage. KEY RESULTS: Three major clusters corresponding to the indica, aus and aromatic subgroups were identified. The largest group was indica, with the salt-tolerant Pokkali accessions in one sub-cluster, while a set of Bangladeshi landraces, including Akundi, Ashfal, Capsule, Chikirampatnai and Kutipatnai, were in a different sub-cluster. A distinct aus group close to indica contained the salt-tolerant landrace Kalarata, while a separate aromatic group closer to japonica rice contained a number of traditional, but salt-sensitive Bangladeshi landraces. These accessions have different alleles at the Saltol locus. Seven landraces - Akundi, Ashfal, Capsule, Chikirampatnai, Jatai Balam, Kalarata and Kutipatnai - accumulated less Na and relatively more K, maintaining a lower Na/K ratio in leaves. They effectively limit sodium transport to the shoot. CONCLUSIONS: New salt-tolerant landraces were identified that are genetically and physiologically distinct from known donors. These landraces can be used to develop better salt-tolerant varieties and could provide new sources of quantitative trait loci/alleles for salt tolerance for use in molecular breeding. The diversity observed within this set and in other donors suggests multiple mechanisms that can be combined for higher salt tolerance.
