54 / 116
Oktober 2017
52
Yield improvement of dryland wheat
cultivars in the Western Cape
– what is the status quo?
W
heat is considered one of the
primary staple foods in South
Africa with an annual consump-
tion of 3,2 million tons. It is esti-
mated that 1,4 million tons will be imported
this year. Yield improvement of new wheat
cultivars is therefore an important aspect
of wheat production in the Western Cape,
which is considered the 'bread basket' of
South Africa.
However, the genetic gain in yield of cul-
tivars released by the ARC-Small Grain in
the Western Cape has never been deter-
mined before and a study was conducted
to determine the progress made in yield
performance of ARC-Small Grain cultivars
released in the Western Cape over the past
three decades.
Study outline
Measuring progress in breeding for grain
yield in drought-affected environments is
frequently confounded by seasonal fluctua-
tions in weather conditions. A method that
eliminates the environmental effect (Tre-
thovan
et al
., 2002) was therefore used to
analyse the data in order to determine the
progress made in yield.
In this study, yield trial data for eleven
ARC-Small Grain cultivars (released be-
tween 1980 and 2012) was collected for the
period 1995 - 2015. These cultivars were cul-
tivated under various environmental condi-
tions in the Swartland (five sub regions) and
Rûens (three sub regions).
The yield trials consisted of between 15 and
30 entries arranged in a randomised block
design with four replicates. Check cultivars,
representing the best adapted cultivars for
the various regions, were included for each
of the yield trials. The mean yield for the
ARC-Small Grain cultivars from each site
and year was calculated and expressed as a
ratio of the trial means.
The ratio, trial mean and mean of the cul-
tivars were regressed against each year to
assess gains in yield over time using linear
regression analysis similar to the proposed
method of Trethovan
et al
., 2002.
In
Graph 1
the mean yield for the ARC-Small
Grain cultivars (SG) from each site and year
was calculated and expressed as a ratio of
the trial means (TM). These values were re-
gressed against each year to assess gains
in yield over time using linear regression
analysis similar to the proposed method of
Threthovan
et al
., 2002.
FOCUS
Winter grain region
Special
DR IAN HEYNS
and
DR ANDRÉ MALAN,
ARC-Small Grain,
DR MARDÉ BOOYSE,
ARC-Biometry and
PROF MARYKE LABUSCHAGNE,
Department Plant Sciences, University of the Free State
Graph 1: Regression of yield trial data for eleven ARC-Small Grain cultivars for the period
1995 - 2014. From Graph 1 it can be seen that measuring progress by slope of the TM (grey)
or the slope of the SG cultivars (orange) on their own, is misleading due to the fluctuations over
years. The ratio smooths these fluctuations and thus provides an indication of yield stability in
the Swartland (the slope = 0) and yield growth of 1% in the Rûens (the slope = 0,01*100 = 1%).