GROWING WHEAT FOR HIGH ALCOHOL YIELD –HOMOGENEOUS AND HETEROGENEOUS APPROACHES - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 172

U TILISATION OF V ARIETAL M IXTURES
One conclusion from the previous section could be that it is difficult to find individual
varieties that will achieve all the requirements for growers and end-users. An alternative
would be to grow a crop comprised of two or more varieties which compensate for each
other's deficiencies and exploit synergies. Mixtures have been cultivated over significant
areas in a number of cereal species, e.g. Gacek et al, [19] reported an annual cultivation of
60,000 ha of spring barley mixtures in Poland, while, in 2000, 18% of the winter wheat area
of Washington State and 13% in Oregon was sown to mixtures [38]. The major motivation
for cultivating mixtures has been to slow the spread of disease and thus reduce or eliminate
the requirement for fungicide application. Mixtures, for example, have been employed, over
an area exceeding 3,000ha in China [81], to counter the problem of rice blast, caused by the
fungus Magnaporthe grisea , with the initial results generating such interest that an increase to
40,000ha was projected for the following year. However, mixtures were also deployed very
successfully in the former German Democratic Republic, to grow barley for malting and
brewing in the 1980s. While this had a very significant effect on reducing the incidence of
powdery mildew and removing the need for fungicide applications [80], the mixture
components were also selected on the basis of their malting quality, thus ensuring that
commercial objectives were achieved.
Commercial utilisation of mixtures has, however, met with some resistance, especially
within the malting and brewing industries. This may reflect a persistent view that growers are
the only real beneficiaries of mixtures [67], but the industry has also cited reduced quality
and, particularly, heterogeneity as a major problem [53]. This view places emphasis on
variety as the major source of variation between samples received for processing and may
underestimate the effects of environment and genotype x environment interaction [68]. This
can be illustrated from research in spring barley, but will be equally applicable in other crops
such as wheat.
Friedt et al. [18] noted the importance of the Czechoslovakian short-strawed mutant
Diamant as a precursor of modern European malting varieties. It is therefore likely that a
considerable number of varieties derive from a narrow gene-pool and will be broadly similar
in malting potential. In contrast with this narrow varietal variation, considerable variation in
nitrogen can exist within a single field due to its topography which is reflected in the range of
nitrogen values obtained from individual grains [2]. Modern malting plants operate on a very
large scale [76] and require to access grain from a large range of sites, as do grain distilleries
using wheat. Prior to malting, barley grain is separated on the basis of variety and nitrogen
content, but, at any given nitrogen level, grain samples from the same variety can differ
considerably in grain texture [11] or malting potential [34]. Similarly, Agu et al. [3] suggested
that differences in grain filling, in wheat, may cause variation in the relationship between
grain nitrogen and alcohol yield. In reality, there is thus a degree of heterogeneity in every
sample of grain going through commercial processing, but it is only when it is sufficient to
cause problems, e.g. in the brewhouse [15], that heterogeneity is seen as problematic.
A mixture derived from varieties with similar ancestry may be no more heterogeneous
than any of its components and Newton et al. [42] were able to demonstrate this with a
mixture of three winter barley malting varieties. A subsequent comparison was made between
four malting varieties and all four possible three-component mixtures, grown at three sites in