Abstract Boron is an essential plant micro-nutrient which can be phytotoxic to plants if present in soils in high concentration. Boron toxicity has been recognised as an important problem limiting production in the low rainfall areas of southern Australia, West Asia and North Africa. Genetic variation for boron toxicity tolerance in wheat has been well-characterised. The efficiency of breeding for boron toxicity tolerance could be greatly enhanced by the development of molecular markers as- sociated with QTLs for tolerance in wheat. A population of 161 doubled haploids from a cross between the toler- ant cultivar Halberd and the moderately sensitive culti- var Cranbrook was used to identify chromosomal re- gions involved in boron tolerance. A combined RFLP and AFLP linkage map of the Cranbrook x Halberd pop- ulation was used to identify chromosomal regions in- volved in the boron tolerance traits measured. Regions on chromosome 7B and 7D were associated with leaf symptom expression. The region on chromosome 7B was also associated with the control of boron uptake and with a reduction in the effect of boron toxicity on root- growth suppression. RFLP markers at the chromosome 7B and 7D loci were shown to be effective in selecting for improved boron tolerance in an alternative genetic background. Halberd alleles at the chromosome 7B locus were associated with the concentration of boron in whole shoots and grain. The concentration of boron in whole shoots and in grain were both related to grain yield in a field trial conducted on soil containing toxic levels of boron. Implications relating to marker-assisted selection for boron toxicity tolerance in wheat are discussed. Key words Boron toxicity · Boron tolerance · Mapping · Wheat · Marker-assisted selection Introduction Boron (B) is an essential plant micro-nutrient which can be phytotoxic to plants if present in soils in high concen- tration. Boron toxicity to crop plants has been recognised since the early 1930s (Christensen 1934), yet it was not until 1984 that it was first recognised in southern Austra- lia in barley growing under dryland conditions (Cart- wright et al. 1984). High concentrations of B have been recorded from soils and plant samples collected from widespread regions of the cereal growing districts of southern Australia (Ralph 1992). Boron toxicity has also been recognised as a problem in the dry regions of West Asia and North Africa and a problem associated with ir- rigation water in many other parts of the world (Gupta et al. 1995). A 17% difference in the grain yield of adjacent areas of barley was related to differences in the concentration of B in shoots just prior to anthesis (Cartwright et al. 1984). Moody et al. (1993) estimated that wheat yield losses of up to 11% could be attributed to B toxicity in southern Australia. Paull (1990) found that wheat plants exposed to high concentrations of B, under glasshouse conditions, responded with reduced vigour, delayed de- velopment, leaf symptoms which include yellowing of leaf tips of older leaves followed by non-specific necro- sis continuing down the leaves and reduced total dry matter and grain yield. The concentration of B in soils in southern Australia has been shown to increase with depth (Cartwright et al. 1984, 1987). The occurrence of B at depth in the soil profile precludes amelioration through soil modification. Communicated by J.W. Snape S.P. Jefferies ( ✉ ) · M.A. Pallotta · J.G. Paull · A. Karakousis J.M. Kretschmer · S. Manning · A.K.M.R. Islam · P. Langridge K.J. Chalmers Department of Plant Science, Waite Campus, University of Adelaide, South Australia 5064 and CRC for Molecular Plant Breeding, Waite Campus, South Australia 5064, Australia A. Karakousis · J.M. Kretschmer · S. Manning · P. Langridge K.J. Chalmers ARC Special Research Centre for Basic and Applied Plant Molecular Biology, Waite Campus, University of Adelaide, South Australia 5064, Australia Theor Appl Genet (2000) 101:767–777 © Springer-Verlag 2000 ORIGINAL ARTICLE S.P Jefferies · M.A. Pallotta · J.G. Paull A. Karakousis · J.M. Kretschmer · S. Manning A.K.M.R Islam · P. Langridge · K.J. Chalmers Mapping and validation of chromosome regions conferring boron toxicity tolerance in wheat (Triticum aestivum) Received: 3 September 1999 / Accepted: 12 February 2000