Fox, GP 2008, 'Biochemical and molecular evaluation of quality for malt and feed barley', PhD thesis, Southern Cross University, Lismore, NSW.
Copyright GP Fox 2008
Barley is the second largest grain crop produced in Australia and has two primary end uses. The first use is the premium market for malt and beer production. The second use is animal consumption. The quality of barley for the range of end uses is influenced by the cultivar itself as well as the growing environment. A detailed understanding of these factors at the genetic and biochemical levels was required to enable breeding program to select for quality improvement. A number of grain and end product quality traits were assessed for genetic and environmental affects as well as their interaction.
Grain size has an important impact on quality and large plump grain is desirable for malt and feed quality. The results from the research conducted in this study clearly show that grain size was affected by cultivar and environmental conditions. Using screenings (< 2.2 mm) and retention (> 2.5mm) data provided information on how cultivars performed under a range of environmental conditions, which included irrigated (water unlimited) to terminal moisture stress (no in crop rain). The results showed a strong genetic component in the variation in grain size and it would be possible to select for increased grain size but also stable grain size when considering cultivars grown under adverse environmental conditions.
The husk content in barley impacts on malt and feed quality. The results in this studied showed there were significant genetic effects as well as environments effects on the level of husk. In addition, it was identified that the genetic regions controlled husk expression were associated with two other quality traits, namely, resistance to kernel discolouration and resistance to pre-harvest sprouting (dormancy). These regions on chromosome 4H and 6H are also associated with previously identified dormancy genes.
Hardness is a trait not usually considered when assessing barley quality but the results from this study showed there are differences in the level of barley hardness, as measured by three methods, as well as differences in the hardness gene sequence. The three hardness methods used showed that barley hardness could be measured independently of the method used, but also that there were significant genetic and environmental effects on hardness. However, the results from sequencing for allelic variation in the hardness genes showed that while there was polymorphism, and hance the transcribed protein had little effect on variation in quality. The cultivars used were malting and feed cultivars and a set of iv breeding lines targeted at malt quality. It may be possible to identify diverse haplotypes from the use of wild relatives or landraces.
This study also investigated the variation in barley for cattle feed quality. Feed quality was determined using an in-sacco dry matter digestibility (ISDMD) assay in fistulated cows as well as three other laboratory assays, namely acid detergent fibre, starch and particle size. These four traits are then used to calculate Net Energy (NE) and Average Daily Gain (ADG). The results show that there were genetic and environmental effects on feed quality. The key trait was the ISDMD assay and there were significant differences between the cultivars tested. The data suggested feed quality was a measurable and definable attribute that could be used in breeding selection.
The final aspect of this study compared the feed data obtained with routine malt quality traits, of friability and hot water extract. There were strong genetic and environmental effects. The malting cultivars generally had the highest level of ADG and NE. The results also showed that there were negative correlations between extract and husk, ISDMD and ADG. Positive correlations were shown between friability and hardness, extract and test weight, and there was only a slight correlation between average daily gain and extract.
An important aspect of this study was the calculation of the genetic component for each trait. This was carried using spatial analysis of mixed models. It was necessary to use this approach so a true estimation of the genetic component could be calculated which would then allow for the calculation of heritability. In plant breeding, the cultivar is not a fixed effect but rather a random variable, hence it was not possible to use normal analysis of variation (ANOVA) models. Rather models were written with cultivars, like environment and field position, as random effects which will allow the effect of each random variable to be accounted for in the analysis. Best Linear Unbiased Predictions (BLUPs) are calculated and presented for all traits.
For all the traits measured in this study, heritability values were calculated to ascertain the level of success in improving these traits through breeding. The range in heritability for grain size was 40 to 90%, husk 30 to 60%, hardness, 40 to 90%, feed quality traits 20 to 80% and malt quality traits 40 to 90%. Generally most traits exhibited a moderate to high level of heritability which indicated genetic improvement was possible through the use of appropriate genetic material.