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Preharvest sprouting research
Unlike the higher levels of preharvest
sprouting tolerance in dryland cultivars, it
has been shown over many years that cul
tivars grown under irrigated conditions do
not display the same levels of tolerance.
A possible reason for this might be that
the dormancy of cultivars grown under ir
rigation conditions is not as high as under
dryland conditions. Previous research has
shown that a reduction in dormancy can
occur when water supply was high during
the later stages of grain filling. Therefore,
the sufficient supply of water at critical
growth stages might reduce dormancy,
possibly explaining the lower levels of pre
harvest sprouting observed in irrigation
cultivars where moisture stress is not a
factor.
Preharvest sprouting evaluation of culti
vars in the Western Cape production area is
relatively new and only nine years of data
are available. It is evident, however, that
the cultivars released for production in the
winter rainfall area, in contrast to the culti
vars under irrigation, have a very good tol
erance to preharvest sprouting.
Graph 3
on
page 72 gives an indication of the prehar
vest sprouting levels of cultivars released
for production in the Western Cape.
From this graph it is clear that the major
ity of cultivars have an excellent to good
tolerance to preharvest sprouting. This is
indicated by the green and yellow bars re
spectively in the graph. Between 70% and
80% of the commercially available cultivars
tend to have a good to excellent preharvest
sprouting tolerance.
Tolerance to preharvest sprouting involves
an interaction between genes and the en
vironment. This means that certain cul
tivars, especially those in the ‘good’ and
‘moderate’ groups can show tolerance to
preharvest sprouting in one year, while the
tolerance can be significantly lower in the
following year.
The temperatures that wheat is exposed to
during the critical grain filling period, may
also have an effect on the dormancy of cer
tain cultivars. Dormancy is usually higher
when temperatures during grain filling are
low, while high temperatures during grain
filling shortens the dormancy period. There
fore, cultivars which are influenced by the
environment, might show various levels of
preharvest sprouting from year to year as
a result of varying temperatures between
seasons.
More recently, preharvest sprouting re
search has moved into a more molecular
direction to enhance pre-breeding for pre
harvest sprouting. Molecular markers are
used to compare marker haplotype combi
nations with the original preharvest sprout
ing cultivar scoring averages.
These marker haplotypes will most prob
ably be used in future to predict the poten
tial preharvest sprouting tolerant class of a
cultivar. This marker technology is meant to
compliment the phenotypic screening and
make the breeding or selec
tion for preharvest sprouting
tolerance more efficient.
Funding for this research was made possible by the Winter Cereal Trust and the Agricultural Research Council.
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October 2018
circular laser-based imager every few milliseconds. It then calcu
lates thousand kernel weight from this. Again, data can easily be
exported to a spreadsheet application for further analysis.
Thus far several hundreds of entries have been both genotyped and
phenotyped over the past year. Preliminary data shows that a lot of
the best alleles (variation of a gene expressing a specific trait) are
already very common in both South African and international germ
plasm screened. This is, however, to be expected since grain size is
such an important aspect of the wheat quality grading system that
breeders generally are on the side of caution when selecting for this
trait, thereby inadvertently narrowing the genetic base from which
they breed. Expanding this genetic base for them to breed from is
thus essential.
Not exploring this after so much work was done in order to relax our
very stringent quality parameters (still very high) would be irrespon
sible. As a wheat breeder I can confidently answer that from our
data thus far it is safe to predict that a part of improving the overall
wheat grain yield of our future cultivars is improving our kernel size.
It will be marginal, but I would like to remind you of the legendary
Sir Dave Brailsford who was the mastermind behind the British cy
cling team’s gold medal run at the 2008 Olympics which reinvigorat
ed British cycling. Sir Brailsford applied the theory of marginal gains
to his cycling team, and the aggregated effect of all the small gains
in performance made them unbeatable.
In the next article I shall explore why water stress tolerance traits
are part of this approach to improve wheat grain yield potential.
Grain SA/Sasol photo competition