Mapping and validation of chromosome regions conferring boron toxicity tolerance in wheat (Triticum aestivum)

Boron is an essential plant micro-nutrient which can be phytotoxic to plant s if present in soils in high concentration. Boron toxicity has been recogn ised as an important problem limiting production in the low rainfall areas of southern Australia, West Asia and North Africa. Genetic variation for bo ron toxicity tolerance in wheat has been well-characterised. The efficiency of breeding for baron toxicity tolerance could be greatly enhanced by the development of molecular markers associated with QTLs for tolerance in whea t. A population of 161 doubled haploids from a cross between the tolerant c ultivar Halberd and the moderately sensitive cultivar Cranbrook was used to identify chromosomal regions involved in boron tolerance. A combined RFLP and AFLP linkage map of the Cranbrook x Halberd population was used to iden tify chromosomal regions involved in the boron tolerance traits measured. R egions on chromosome 7B and 7D were associated with leaf symptom expression . The region on chromosome 7B was also associated with the control of baron 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 b e effective in selecting for improved boron tolerance in an alternative gen etic background. Halberd alleles at the chromosome 7B locus were associated with the concentration of boron in whole shoots and grain. The concentrati on of boron in whole shoots and in grain were both related to grain yield i n a field trial conducted on soil containing toxic levels of boron. Implica tions relating to marker-assisted selection for boron toxicity tolerance in wheat are discussed.