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lems with the test, which was voiced to
ARC-Small Grain. Research into the various
factors, aside from high
alpha
-amylase ac
tivity as a result of sprouting that might con
tribute to low falling number, was therefore
necessitated. Intensive trials were execut
ed in order to justify the necessity of the
falling number system as part of the grading
regulations.
Many wheat producing areas in South Af
rica, especially the Eastern Free State, are
highly subjected to the risk of preharvest
sprouting due to summer rainfall that oc
curs just prior to or during harvest. Since
preharvest sprouting is closely related to
falling number, a lot of effort and energy
were put into preharvest sprouting research
over the past 20 years.
The impact of preharvest sprouting dam
age on the wheat industry in South Africa
has been well documented. Following the
initiation of a selection and research pro
gramme aimed at combatting susceptibility
to preharvest sprouting damage in the early
1990s, various methods to minimise the
damaging effects of preharvest sprouting,
were investigated.
Research has shown than the genotypic
variation in preharvest sprouting in South
African cultivars is dominant, indicating that
progress in the development of cultivars
with sprouting tolerance is feasible. Dur
ing the past decades, the development of
wheat cultivars with high levels of seed dor
mancy has been an objective of all breeding
companies in South Africa.
Preharvest sprouting results of commer
cial cultivars are available since 1991. Over
the past 27 years more than 150 wheat culti
vars of the three breeding institutions have
been evaluated for their preharvest sprout
ing resistance.
Significant progress has been made with
the release of especially winter wheat culti
vars with high levels of preharvest sprout
ing tolerance from only 23% of cultivars,
showing tolerance in the early 1990s to al
most 60% currently (
Graph 1
).
Research clearly showed that South African
winter wheat cultivars can be categorised
into three major groups, namely those that
are highly resistant to preharvest sprout
ing and others that are highly susceptible.
The third group includes cultivars that are
strongly influenced by the environment and
includes both ‘good’ and ‘moderate’ types.
Without reference to individual cultivars,
Graph 1 gives a good indication of the
progress that has been made in the devel
opment of winter wheat cultivars with high
levels of preharvest sprouting tolerance
over the past 20 years. This graph shows the
preharvest sprouting groupings of all the
commercial cultivars that were evaluated
and included in the
ARC-Small Grain Annual
Production Guidelines
in a specific year.
Commercial cultivars were evaluated for
their preharvest sprouting tolerance and
the preharvest sprouting value that each
cultivar received, is the average of 120 in
dividual ears over three different localities.
According to the values, cultivars were
grouped into either ‘excellent’, ‘good’, ‘mod
erate’ or ‘poor’ groupings. These groups are
then given a percentage depending on the
number of cultivars evaluated in that spe
cific year.
The preharvest sprouting evaluation pro
gramme was initiated at the beginning of
the 1990s. During this time most of the dry
land wheat cultivars had poor preharvest
sprouting tolerance. This is shown by the
red colour of the bars in Graph 1.
As a result of continuous evaluations and
adaptations to the respective breeding
programmes, the preharvest sprouting tol
erance of cultivars improved significantly
to such an extent that only two out of the
19 cultivars (10,5%) that are currently com
mercially available, have poor preharvest
sprouting tolerance compared to the almost
60% in 1992.
Similar to the dryland cultivars, more than
20 years of preharvest sprouting data are
available for irrigation cultivars.
Graph 2
shows the percentage of cultivars with ‘ex
cellent’, ‘good’, ‘moderate’ or ‘poor’ prehar
vest sprouting tolerance respectively for
each year from 1994 to 2018.
The number of cultivars with poor pre
harvest sprouting tolerance (indicated by
red bars) has also decreased over the last
20 years from almost 58% in 1994 to 38%
in 2018 (Graph 2). However, the number of
cultivars with excellent preharvest sprout
ing tolerance (green bars) is still very low.
The majority of current commercial culti
vars either has good or moderate prehar
vest sprouting tolerance.
73
October 2018
Preharvest sprouting screenings in the
molecular laboratory.
A sprouted wheat ear.