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November 2017
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The real facts
behind preharvest sprouting
and aluminium toxicity
A
cid soils are widespread in the
major wheat producing regions of
South Africa. More than two thirds
of the arable soils of the eastern
part of South Africa – especially the Eastern
Free State and KwaZulu-Natal – are affected
by soil acidity. The major limiting factor to
agronomic productivity in these soils is alu-
minium (Al) toxicity.
Preharvest sprouting is the premature ger-
mination of wheat kernels in the ear, while
still attached to the mother plant. This oc-
curs sporadically as a result of rain and pro-
longed moist conditions in the critical few
weeks around harvest time. This leads to
biological changes in the grain that lower
grain yield, hectolitre mass and flour qual-
ity, resulting in huge economic implications
for both producers and end-users. There is
a wide range of variation in the preharvest
sprouting tolerance in South African wheat
cultivars, ranging from good to poor.
In a previous study it was shown that the
pH of the soil had no effect on the prehar-
vest sprouting resistance of wheat cultivars
grown in those soils in the susceptible or
resistance groupings (red and green groups
in
Graph 1
).
However, lower pH values, in other words
increased soil acidity, led to higher levels
of preharvest sprouting resistance suscep-
tibility of the moderately resistance culti-
vars (yellow group). We also know that the
moderately resistant group of cultivars is
in general more prone to environmental
stresses than the susceptible or resistant
group.
A cultivar in this group may have a good
preharvest sprouting resistance in certain
years under certain conditions, while the
same cultivar can show susceptibility to
preharvest sprouting resistance under dif-
ferent conditions.
Throughout the years, various cultivar reg-
istration publications reported that lines or
cultivars with good resistance to preharvest
sprouting resistance have poor tolerance to
aluminium in the soil and vice versa. It has
also been shown that lines or cultivars with
moderate aluminium tolerance usually have
moderate resistance to moderate suscepti-
bility to preharvest sprouting resistance.
ON FARM LEVEL
Preharvest sprouting / Wheat / Harvest
Technology
DR ANNELIE BARNARD, DR SCOTT SYDENHAM
and
HESTA HATTING,
ARC-Small Grain, Bethlehem
1: A wheat field suffering from aluminium
toxicity.
2: A wheat ear showing extreme preharvest
sprouting.
3a to 3c: Screening for preharvest sprouting
resistance and aluminium in the laboratory
and through marker assisted selection.
4: A gel photo of a 3% high resolution
agarose gel of the
ALMT1
marker. The four
different alleles of the
ALMT1
gene is visible
in the various lanes of the gel.
1
3a
4
3b
3c
2