GENETIC-ANALYSIS AND PHYSIOLOGY OF A TRAIT FOR ENHANCED K+ NA+ DISCRIMINATION IN WHEAT/

Variation for K+ and Na+ accumulation at low salinities in hydroponic (water) culture were observed in shoots of different wheat species. Gr eater discrimination (in favour of K+ and against Na+ accumulation) wa s shown by hexaploid bread wheat (Triticum aestivum L.) than by tetrap loid durum wheat (T. turgidum L.). Since Aegilops tauschii Cosson (A. squarrosa L.), the source of the D genome in bread wheat, also exhibit ed high discrimination between K+ and Na+, it was concluded that the c haracter resided in the D genome. Studies of aneuploid bread wheat lin es and disomic substitution lines of D genome chromosomes for their A and B genome homoeologues in durum wheat cv. Langdon revealed that the trait was controlled by the long arm of chromosome 4D. Since the aneu ploid and disomic substitution lines showed better relative salt toler ance than durum wheat, but had lower yield potentials, we recombined c hromosome 4D with chromosome 4B in a tetraploid wheat background using a homoeologous pairing mutant. This produced families of 4D/4B recomb inant lines, some of which exhibited the enhanced K+/Na+ discriminatio n trait. RFLP analysis confirmed that the trait was controlled by a si ngle gene (Kna1) which was completely linked to five markers on the di stal third of the long arm of 4D. a second cycle of homoeologous recom bination was employed to remove the distal 4D genetic material from th e recombined Kna1 4B/4D chromosome and to map Kna1 in greater detail. By this strategy, Kna1 was mapped within a short 2 cM region. Genetic analysis of K+:Na+ ratios showed very high LOD scores in this region f or plants grown in solution culture, but lower values for plants grown in the field. In general, recombinant lines which exhibited the enhan ced K+/Na+ trait were slightly more tolerant of salinity in the field and in sand culture than recombinants lacking the trait. There was, ho wever, considerable variation between individual lines. Ion discrimina tion and relative tolerance were also higher in a Kna1 recombinant (li ne no. R3) than in a kna1 recombinant (line no. R165) in sodic conditi ons. In these two lines the enhanced K+/Na+ discrimination trait did n ot alter responses to low potassium or calcium supply.