Black point formation in barley: environmental influences and quantitative trait loci

Black point and kernel discoloration of barley both appear to occur under conditions of high humidity at grain fill. Both of these traits are likely to result from the enzymatic oxidation of phenolic compounds to quinones and the transformation of those oxidation products to brown or black pigments during high humidity. However, even though black point symptoms are quite distinct from other types of kernel discoloration, black point of barley has not previously been the sole focus of environmental studies or quantitative trait locus (QTL) analysis. We have evaluated black point tolerance in doubled haploid progeny of Alexis/Sloop and mapped QTLs on chromosomes 2H and 3H. We have also established that the occurrence of low vapour pressure deficit, high humidity, and low temperatures is associated with the formation of black point in susceptible varieties. These environmental conditions probably create a moist environment during grain development so that the developing grain cannot dry out. Stress or wounding to the embryo caused by this environment might then lead to black point formation. The results of this study will enable the use of comprehensive genetic and biochemical approaches to develop a more detailed understanding of this disorder.

Quantitative trait loci controlling kernel discoloration in barley (Hordeum vulgare L.)

Barley kernel discoloration (KD) leads to substantial annual loss in value through downgrading and discounting of malting barley. KD is a difficult trait to introgress into elite varieties as it is controlled by multiple genes and strongly influenced by environment and maturity. As the first step towards marker assisted selection for KD tolerance, we mapped quantitative trait loci (QTLs) controlling KD measured by grain brightness [Minolta L; (Min L)], redness (Min a), and yellowness (Min b) in 7 barley populations. One to 3 QTLs were detected for grain brightness in various populations, and one QTL could account for 5–31% of the phenotypic variation. The QTL located around the centromere region of chromosome 2H was consistently detected in 6 of the 7 populations, explaining up to 28% of the phenotypic variation. In addition, QTLs for grain brightness were most frequently identified on chromosomes 3H and 7H in various populations. Australian varieties Galleon, Chebec, and Sloop contribute an allele to increase grain brightness on chromosome 7H in 3 different populations. A major gene effect was detected for grain redness. One QTL on chromosome 4H explained 54% of the phenotypic variation in the Sloop/Halcyon population, and was associated with the blue aleurone trait. A second QTL was detected on the long arm of chromosome 2H in 3 populations, accounting for 23–47% of the phenotypic variation. The major QTLs for grain yellowness were mapped on chromosomes 2H and 5H. There were strong associations between the QTLs for heading date, grain brightness, and yellowness. The molecular markers linked with the major QTLs should be useful for marker assisted selection for KD.