This sweetness is provided mainly by the sucrose content. The highest sucrose content
for a single mutant gene is provided by the shrunken 2 (sh2) gene. It generates a
sucrose content as high as 35% compared with 15% to 20% from the sugary1 mutant
used in ordinary sweetcom ( Creech, 1968). Higher sucrose contents can be generated
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by using combinations of sh2 with other mutant genes such as the sul gene but this
complicates the breeding process and can also impair germination percentages
because of the reduction in starch content (Kaukis and Davis, 1986).
We have chosen to work mainly with the sh2 mutant in this project although we did
investigate the brittle i(btl) mutant as an alternative. Even amongst sh2 genotypes
there are large differences in sweetness and flavour suggesting the influence of
modifying genes. Our selection in this project is on these modifiers. We have also
sought to select genotypes that maintain a high level of sweetness for an extended
time after fertilisation. This characteristic has the virtue of permitting delays in
harvesting with no appreciable reduction in sweetness . (The sh2 gene also inherently
confers longer shelf life than most other mutants). By conducting the taste evaluations
at 28 to 30 days after flowering (compared with the usual 25 days) we have sought to
find genotypes with enhanced retention of sweetness in the field.
A distinction should be drawn between sweetness and taste. Sweetness is an important
component of taste but taste also includes other flavours that can vary greatly. Some
of them, such as the "beany" and "grassy" flavours are considered undesirable. Taste
can also be taken to include texture. Texture can be watery, gritty or creamy, the latter
being favoured. Creamy texture in sweetcorn is thought to be associated with a high
level of water soluble polysaccharides. These compounds tend to be lacking in
shrunken 2 genotypes.
A successful outcome in terms of the objectives described above would provide
consumers in the major cities with a much better quality fresh sweetcorn product for a
significant period of the year (May to July). It would also give the industry the
potential to mount a large processing industry in tropical areas with year round
growing capability and the potential to export to Asian markets.