Research Highlights of the CIMMYT Wheat Program 1999-2000

Strategies for Further
Improving Yield Potential
“Balancing” yield component
architecture and biomass
Contrasting the performance of top yielding
durums with top yielding bread wheat genotypes
may produce models for identifying alternate
avenues to obtaining higher yield for either crop.
Pfeiffer et al. (1996) suggested that lower numbers
of spikes m -2 and grains m -2 in durums compared
with bread wheat should receive special attention
in durum improvement, since past experience
indicated superior bread wheat performance was
associated with number of spikes m -2 . Figure 4
discloses a gradual correction of this delinquency
in contemporary durum wheats, revealing a
converging of yield architecture in durum and
bread wheat.
Earlier efforts to increase biomass focused on
manipulating spikes m -2 and, later, on augmenting
the number of grains spike -1 , both of which are
traits suitable for phenotypic selection. The avenue
of selecting for grains m -2 via a higher number of
grains spike -1 proved superior in raising GYP.
Negative effects on spikes m -2 were minor and
1000-grain weight could be maintained. Over 1997-
99, the simultaneous increase in both spikes m -2
and grains spike -1 produced the highest increase in
grains m -2 , GYP, and biomass. The balance in yield
components may have approached a near optimal
constellation, as results from crop comparison
suggest. With limited scope for increasing the
partitioning of assimilates to the grain, future
progress has to be based on increased biomass.
Exploring physiological strategies to
enhance grain yield potential
Physiological strategies that can be applied
empirically to accelerate the rate of breeding
progress include increase radiation use efficiency
(RUE) and, therefore, total plant biomass, increased
grain number, and increased kernel weight. These
three strategies do not address the issue of how to
provide extra assimilates during the spike growth
period (i.e., booting) so that higher grain number
and grain weight potential can be achieved. Such
strategies are discussed in more detail elsewhere
(Reynolds et al., 1999; Reynolds et al., 2000). These
strategies should be incorporated into analytical
and empirical selection approaches.
Grain Yield
Biomass
Harvest Index
Straw Yield
Spikes/m 2
Grains/spike
Grains/m 2
1000 G Weight
Spike Weight
Kernel G Rate
Biom Prod Rate
Grain Biom Prod Rate A
Grain Biom Prod Rate B
Vegetative Growth Rate
Days Heading
Days Maturity
Grainfill Duration
Plant Height
Test Weight
1997-99
1994-96
1991-93
Grain Yield
Biomass
Harvest Index
Straw Yield
Spikes/m 2
Grains/spike
Grains/m 2
1000 G Weight
Spike Weight
Kernel G Rate
Biom Prod Rate
Grain Biom Prod Rate A
Grain Biom Prod Rate B
Vegetative Growth Rate
Days Heading
Days Maturity
Grainfill Duration
Plant Height
Test Weight
1997-99
1994-96
1991-93
-5 0 5 10 15 20
% Difference from check average
Figure 3. Changes in agronomic components in durum in
three time periods: comparison between the respective 3
highest yielding lines and 5 historical checks.
Data source: Agronomy yield trials, 1991-1999.
-25 -20 -10 0 10 20 30
% Difference from bread wheat
Figure 4. Changes in agronomic components in durum in
three time periods: comparison between the respective 3
highest yielding durum and bread wheats.
Data source: Agronomy maximum yield trials, 1991-1999.
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