Genetic routes to modulate rate of dry-matter disappearance of barley grain in the rumen of cattle
Jewell, Jeremy Burke.
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Recent research has identified important characteristics of barley grain as feed for cattle. Of these, low ruminal dry-matter digestibility (DMD) is of particular importance as it is highly correlated with animal performance and with animal health. This research attempts to identify genetic loci that contribute to the ruminal DMD of barley grain. The utility of the barley ant18 mutation for decreasing ruminal DMD was investigated. The DMD of several barley cultivars and their ant18 mutations was investigated in a randomized complete block design in two environments. Genotype by environment interaction was present: in the greenhouse the DMD of ant18 mutants was less than that of the wildtype, and in a dryland field the reverse was true. Because of this interaction, ant18 is not likely to be a reliable method of modulating DMD. With the aim of identifying markers for marker-assisted selection (MAS), a 123-member inbred population was developed from a cross of Haxby and PI 28624. PI 28624 is a low DMD accession from the USDA barley collection.The grain of this population was evaluated for DMD at the F6 generation and F5 DNA genotyped using SSR and AFLP markers, allowing genetic map construction and quantitative trait locus (QTL) analysis. Two QTL were detected on chromosome 6H and 7H explaining 19 and 17% of phenotypic variation, respectively. Due to the low estimated genome coverage of this map (50 to 65%), 86 F7 lines were genotyped using the GoldenGate SNP genotyping technology. Use of this technology allowed accurate assessment of genome coverage, which is quite complete with the exception of the extreme short arms of 2H, 5H, and 6H. 3H and 6H, though apparently quite complete, are of much shorter centiMorgan length than the consensus maps of these chromosomes. Possible causes of this phenomenon are discussed. In addition to the previously detected QTL, two new QTL for DMD were detected in this F7 sub-population, on chromosomes 1H and 7H. These QTL may be useful for MAS if they can be validated in other populations. This population will be useful for other genetic studies in barley.