Variation and inheritance of sodium transport in rice

Abstract

Sodium transport in rice is characterised by large variability between individual plants, and large environmental interaction. As a result of these two factors, plant sodium content is a continuous variable which is not distributed normally. This applies both to the quantity of sodium in the plant and to the concentration of sodium on a unit fresh or dry weight basis. This variability is in part because the transpirational by-pass flow, dependent upon root anatomy and development, contributes to sodium uptake. Variability in sodium content within designated cultivars is heritable and line selections diverge during recurrent selection, suggesting that selection is working on residual heterozygosity rather than on a family of homozygous lines. Varieties differ in average sodium uptake into the plant but the direct correlation of this with survival is weak. This is because other independent characters are important (and these have not been combined by natural selection nor by chance) and because overall performance is confounded by the spurious advantage of the tall (non-dwarf) plant type. This advantage is spurious because much of it is due to plant size rather than to any genetic information for salt tolerance. The benefit deriving from plant size will not be heritable in crosses with genotypes of the improved (dwarf), high-yielding plant type because the dwarfing genes are dominant. Sodium transport is heritable in crosses, and the results presented show that both low sodium transport and low sodium to potassium ratio can be selected independently of plant type. This allows the selection of dwarf plants (which are agronomically desirable) with low sodium transport (which will improve salt tolerance).