Research Highlights of the CIMMYT Wheat Program 1999-2000

the variation in yield (Figure 2). Other work has
demonstrated the effectiveness of using the trait in
selection nurseries to predict performance of
advanced lines in heat stressed target environments
(Reynolds et al., 1997, 1998). When CTD was
compared with other potential selection traits (grain
number, biomass, phenological data, and yield)
measured in the selection environment, none of the
other traits showed a greater association with
performance in the target environment than CTD.
The trait was also studied in three populations of
homozygous sister lines under drought stress. CTD
showed a highly significant association with yield
under drought when measured pre-anthesis in all
populations. CTD measured during grainfilling
tended to show a better association when measured
in the morning (Table 3).
In addition to yield, breeding objectives must take
into account multiple factors, such as disease
tolerance and phenology. Therefore, it would be
logical when incorporating CTD into a selection
protocol, to select for relatively genetically simple
traits such as agronomic type and disease resistance
in the earliest generations (e.g., F 2
-F 3
). Selection for
CTD could be employed in subsequent generations,
when more loci are homozygous, and perhaps in
CTD ( o C)
6.0
5.5
5.0
4.5
4.0
y= 0.0004x + 3.0711
r 2 = 0.44
3.5
2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 6,500
Yield (kg ha -1 )
Figure 2. Relationship between canopy temperature
depression (CTD) measured during grainfilling and yield of
random derived F 5:8
sister lines from the spring wheat cross
Seri-82 x SieteCerros-66, Ciudad Obregon, Sonora, Mexico,
1996 - 1997.
Source: Reynolds et al., 1999.
preliminary yield trials. (Table 4). The possibility of
combining selection for both CTD (on bulks) and
stomatal conductance (on individual plants) is
another interesting possibility. In recent work at
CIMMYT (Gutiérrez-Rodríguez et al., 2000),
stomatal conductance was measured on individual
plants in F 2:5
bulks and showed significant
phenotypic and genetic correlation with yield of F 5:7
lines.
Aerial infrared imagery. CTD can be estimated
remotely using aerial IR imagery. Work conducted
in Ciudad Obregon, Sonora, Mexico, showed that
aerial IR images had sufficient resolution to detect
CTD differences on relatively small yield plots (1.6
m wide). Data were collected using an IR radiation
Table 3. Correlation between CTD measured pre-heading and
during grainfilling on 25 recombinant inbred lines of Seri 82/
Baviacora 92, at different times of day, at two environments
in Mexico, 1999-2000.
Correlation with yield
Trait C. Obregon (810) Tlaltizapan
CTD mean 0.85** 0.84**
CTD AM prehead 0.82** 0.79**
CTD AM grainfill 0.79** 0.68**
CTD PM prehead 0.85** 0.72**
CTD PM grainfill 0.37 0.06
Days to maturity 0.29 -0.22
** Statistical significance at P>0.01.
Table 4. Theoretical scheme for incorporating physiological
selection criteria into a conventional breeding progam
showing different alternatives for when physiological traits
could be measured, depending on resources available.
Breeding generation when selection to be conducted
Trait All generations F3 F4-F6_ PYTs/Advanced lines
Simple traits
Disease
visual
Height
visual
Maturity
visual
Canopy type
visual
Complex traits
Yield visual yield plots
CTD small plots yield plots
Porometry plants small plots yield plots
Chlorophyll plants small plots *
Spectral reflectance small plots yield plots
* Chlorophyll is sufficiently stable with respect to interaction with environment for
additional measurements not to be necessary.
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