Pyramiding QTLs to improve malting quality in barley: gains in phenotype and genetic diversity

The ability of barley (Hordeum vulgare L.) breeders to deliver germplasm that combine elite malt quality characteristics, disease resistances, and important agronomic traits has been greatly enhanced by the use of molecular marker technologies. These technologies facilitate the rapid transfer of desirable traits from diverse, elite, germplasm into locally adapted varieties. This present study sought to obtain an additive genetic effect by combining favourable alleles associated with the malting quality of two elite donor parents (Harrington and Morex) such that the resultant progeny would possess quality superior to either parent. Analysis of genetic diversity, based on whole-genome profiling with 700 DArT markers, showed clear separation of the BC₆F₁-derived doubled haploid lines from existing malting barley germplasm, indicating they represent a distinctly different source population for genetic improvement. Micro-malting quality results of the BC-derived lines showed substantial quality improvements, compared with the recurrent parent. Malt extract levels were increased by 1.5–2.0%, while diastase levels increased from approximately 320 WKE to 400–460 WKE. Similarly, α-amylase levels were increased from 160 units to between 218 and 251 units, and wort viscosities lowered from 1.90 cps to 1.72–1.82 cps. Other quality improvements include increases in β-glucanase levels from 375 to between 447 and 512 units, and reductions in wort β-glucan levels by 30–60%. Whilst the genetic gains compared to the recurrent parent were impressive, quality of the derived lines were largely equivalent to the levels now available in the recently released varieties, Buloke and Flagship. In a few cases, the backcross-derived lines also showed similarities to the original donors, Harrington and Morex, but in none of the cases did quality of these lines exceed those of either Harrington or Morex.