Identification of genetic loci affecting amylose content and agronomic traits on chromosome 4A of wheat

 Chromosome 4A of wheat carries the Wx-B1 gene encoding the granule-bound starch synthase involved in amylose synthesis in the endosperm. To determine the pleiotropic effects of this locus and effects of independent QTLs on agronomic traits, genetical analysis of chromosome 4A was conducted using 98 single-chromosome recombinant substitution lines derived from a cross of Chinese Spring and Chinese Spring (Kanto107 4A) with a low amylose content due to the null Wx-B1b allele. For amylose content, most of the genetic variation was explained by the allelic difference at the Wx-B1 locus. An additional QTL of minor effect was mapped in the 6.2-cM Xbcd1738/Xcdo1387 interval on the short arm, where the allele from Kanto107 led to an increase in amylose content. Field trials over two seasons revealed a pleiotropic effect of Wx-B1, or else the effect of a closely linked QTL, on ear emergence time. A QTL linked to Wx-B1 was detected for plant height. For plant yield and its components, there was no evidence for significant main effects associated with Wx-B1 or adjacent regions. One plant-yield QTL was identified by RFLP markers on the short arm and this was identical to QTLs controlling spikelet number/ear and grain weight/ear. At these QTLs for agronomic traits, alleles from Kanto107 contributed to an earlier emergence time, a height reduction and an yield increase. Received: 10 August 1998 / Accepted: 3 November 1998