The effects of selection for sodium transport and of selection for agronomic characteristics upon salt resistance in rice (Oryza sativa L.)

Abstract

A multiple cross was constructed with the aim of combining component traits for the complex salinity resistance character. The aim was to combine donors for physiological traits with the agronomically desirable semidwarf/intermediate plant type and with the overall salinity resistance of the traditional tall land races. We report a study of selection strategies in the resulting breeding population. The effects of early selection for agronomic traits and early selection for low sodium transport were compared with a control population in which minimal selection was practised. Conventional selection for agronomic characters at early generations selected against low sodium-transporting (and thus potentially salt-tolerant) genotypes. In contrast, mild early selection for low sodium transport enriched the population in potentially salt-resistant genotypes but did not select against agronomic (semi-dwarf/intermediate) genotypes. It is concluded that selection for agronomic traits should be made after selection for salt resistance and, ideally, should be delayed until the population has reached near-homozygosity.

Sodium and potassium transport to the xylem are inherited independently in rice, and the mechanism of sodium: potassium selectivity differs between rice and wheat

“…Our results are one of the first rigorous assessments of the heritability of quantitative physiological traits involved in the tolerance of salinity. The finding that sodium transport in rice has a narrow-sense heritability of over 0-4 supports the view that selection for low sodium transport is feasible (Yeo 1992;Garcia et al 1995). The data are in close agreement with results for japonica rice obtained by a different methodology (diallel analysis) where narrow-sense heritabiiities of 0-49 (sodium), 0-53 (potassium) and 0-51 (sodium to potassium ratio) were found (Lee 1995).…”

“…Significant differences in the frequency distribution of sodium transport were evident after three cycles of repeated selection (differences after the first and second cycles may have been obscured by variability) and lines segregated further in the fourth and fifth cycles of selection. Gregorio & Senadhira (1993) and Garcia et al (1995) both concluded that selection in breeding populations designed for salinity tolerance should be delayed because traits are not fixed in the early generations. We carried out the heritability measurements at generations in which the material would slill be segregating for sodium transport but in which variability had decreased sufficiently to allow estimation of line means; we assessed the single cross (1R55I78) at F4/F, and the multiple cross {IR59462) at FS/F4.…”

“…There is an overwhelming eotisensus in the literatute that exeessive concentration of salts in the cytoplastn is damaging to the functioning of eukaryotic cells (see e,g, reviews by Flowers et al 1977Flowers et al , 1986Greenway & Munns 1980;Munns & Tertnaat 1986), It is therefore difficult to see how sodium aeeumulalion, at least in excess of that which could be used for osmotic adjusttnent, can be of advantage to a higher plant, Sodiutn uptake in riee is exeessive by this definition and within a genotype is associated with (Yeo et al 1991), However, sodiutn uptake aecounted for only a stnall proportion of the vat iance in survival, as a tneasure of overall perfortnanee, when a large number of genotypes of rice were investigated (Yeo et al 1990), The reasons for this are exatnined in detail by Yeo et al (1990), Yeo (1994) and Flowers & Yeo (1995) and ean be sutntnarized as follows. Salt toleranee in riee is a eotnplex eharaeter eomprising a nutnber of cotnpotient traits (whieh inelude sodiutn uptake and eotnparttnetitalizatioti).…”

“…1990Yeo etal. , 1991Gregorio & Senadhira 1993;Garcia et al 1995), Sinee any breeding progratntne depends upon the effieieney with whieh seleetion ean be perfortned for the traits of interest, a major aitn of our studies was to begin a rigorous assessment of the tiatfow-sense heritability of relevant traits. In this paper we itivestigate the heritability and inter-relationship of sodium and potassiutn uptake.…”

Gene Expression Profiles during the Initial Phase of Salt Stress in Rice

“…These phases could be correlated with several mechanisms. Several biochemical pathways, ion and metabolite transport processes, hormonal control, cell structure and organ growth, and signaling have been identified (Yeo et al, 1990;Flowers and Yeo, 1995;Garcia et al, 1995;Price et al, 1997;Hasegawa et al, 2000). It is not possible to correlate the physiological terms and only partially understood mechanisms in the context of this microarray analysis of plant salinity stress.…”