Purpose and context of the project. The objective of the project is to evaluate promising new selection criteria to complement traditional selection methodologies for yield in wheat. Wheat is grown on some 220 million ha worldwide, about half of which is in developing countries and CIMMYT has played a major role in increasing the productivity of wheat globally. Nonetheless, demand for wheat is expected to grow by approximately 1.3% per year world-wide and by approximately 1.8% per year in developing countries. Improvement in genetic yield potential since the initial impact of The Green Revolution stands at 0.88% per year and is clearly too low to keep pace with future demand. Given the environmental implications associated with increasing land use, and the cost and complexity of further reducing the relatively small yield gaps in high production areas, improving genetic yield potential of wheat would seem to be a highly cost effective solution for meeting future demands. These facts suggest an urgent need to develop more efficient wheat breeding methodologies to complement existing techniques, as well as to identify new traits which will drive faster yield gains through exploiting the true biological yield potential of the wheat crop. There is now a strong body of evidence emerging indicating that physiological traits have very real potential for improving the efficiency of yield gains in wheat. Research conducted at CIMMYT and in Australia has revealed a consistent correlation between increase in yield potential and changes in stomatal aperture related traits (SATs); i.e stomatal conductance, canopy temperature depression (CTD) and 18O and 13C stable isotope composition.
Names of collaborating researchers and institution
___________________________________________________________________
Researcher Institution
___________________________________________________________________
Mexico:
Dr. M Reynolds, Physiologist CIMMYT
Dr. MvanGinkel Head of Bread Wheat Breeding CIMMYT
Dr. R. Trethowan Bread Wheat Breeder CIMMYT
Dr. Jose Crossa Biometrician CIMMYT
Dr. Prabhu Pingali Economist CIMMYT
Australia:
Dr. A. Condon Physiologist CSIRO
Dr. G. Rebetzke Geneticist CSIRO
Dr. R. Richards Wheat Breeder CSIRO
Prof. G. Farquhar Physiologist ANU
Expected results and value. The technologies developed by this project should significantly improve the efficiency of early generation and advanced line selection, as well as provide a better knowledge base from which to develop more strategic crossing plans, through the identification of yield enhancing traits in new and conventional sources of germplasm. The technologies being developed are equally applicable to collaborating countries and NARS breeding programs. Shifting the wheat yield frontier will have an immediate impact in terms of raising farm level yields as well as in reducing unit production costs. As a consequence domestic food security will be improved and wheat will be available at a lower price thus benefiting the poor consumers, both rural and urban. If this research can improve the rate of increase in genetic yield gains by just one tenth (i.e., from 1.0 to 1.1% p.a.), the annual output will reach 685 m tons by 2020, an extra 15m tons of wheat per year, representing a value of approximately US $ 3 billion p.a. ($200 per ton).
Likely direction of future research activities. Results from this project could be followed up as follows: (i) Develop molecular markers for SATs and other yield enhancing traits to provide additional tools for improving breeding efficiency. (ii) Further exploit the true biological yield potential of wheat in different environments (including marginal environments) based on physiological insights gained from the current work. (iii) Develop capacity
in NARS to fully implement the use of physiological selection criteria in breeding

1) Quantitatively Evaluate Genetic Gains Associated with SATs Using Alternate Selection Methodologies.
a) Quantitatively evaluate genetic gains in early generation breeding populations using SATs as indirect selection criteria in unselected sister lines. SATs (canopy temperature CT, leaf porosity-POR, and carbon isotope discrimination-CID) were measured on 5 populations of random lines grown in small observation plots (1.6 m2) and compared with yields of the same lines in larger plots (6.4 m2). Trials were sown in replicated lattice designs in Obregon, NW Mexico a temperate, irrigated high radiation environment. CANOPY TEMPERATURE/DEPRESSION (CT/D). Canopy temperature was measured between 3-5 times on sunny, relatively windless days during both the booting and grain-filling stages. The genetic correlations between CT/D and yield are presented (Table 1). For the most part correlations were significant. Higher correlations were obtained with CT measured in 2003 than with CTD measured in 2002. Although the result is confounded by year, the trend is consistent with last years results were CTD and CT were measured simultaneously on advanced lines in the trial Tonyp-Padres, and CT was found to show a higher correlation with yield than CTD. Genetic correlations between SATs and yield that were both measured on large plots are presented for 3 populations of RILs and one set of advanced lines pertaining to experiments in Thrust-3 of this project (Table 2); results are very similar. LEAF POROSITY (POR). Leaf porosity was measured using the latest version of the Thermoline viscous-flow porometer. All small observation plots of the 5 populations of random lines were measured twice, once during late-booting/ear-emergence stage and then during grain filling. Because of persistent cloud during February, it was only possible to measure large plots once, around anthesis. Six individual sunlit leaves were sampled in each plot (1.6 m2 and 6.4 m2) at each sampling time, taking about 1 minute/plot before flowering and a little longer during grain filling. The genetic correlations of small-plot POR and large plot yield in 2000/01 and 2001/02 cycles are presented (Table 1- POR). Genetic correlations were moderate-strong in both cycles. Strength of correlations varied among populations, and was strongest for the "7C/Seri" population and weakest for "Cross 5". There was no indication that the correlations were consistently stronger for post-anthesis measurements than for pre-anthesis measurements. CARBON ISOTOPE DISCRIMINATION (CID). Leaf samples were taken during the vegetative stage and grain at maturity from small plots of 4 populations during the 01-02 cycle and analyzed by collaborators at CSIRO in early 2003. The genetic correlations of CID with yield in 2001/02 and 2002/03 cycles are presented (Tables 1 & 2). The correlations are comparable with that of canopy temperature. Samples were also taken from grain of small plots in 5 populations at both sowing dates in the current cycle (2002/03) and have been sent to CSIRO.
b) Quantitatively evaluate genetic gains in F5 breeding populations using SATs as indirect selection criteria on random F4 individual plants in unselected F3:4 bulks. This experiment was not repeated in 2002/03 due to the poor heritability found in previous cycles between POR measurements on single plants with those measured subsequently in yield plots.

c) Semi-quantitatively compare a) with genetic gains realised from SAT-assisted selection on breeder-selected F4 lines. CTD was measured on breeders selected F3:4, and F4:6 plots (modified bulk), derived from 10 elite x elite crosses. Analysis pending results of breeders yield trials which were put on hold in 2002/03 due to budget constraints

d) Semi-quantitatively evaluate the potential complementarity of visual and physiological selection criteria in resoure-use efficient breeding strategy (Selected Bulk). Analysis pending results of breeders yield trials which were put on hold in 2002/03 due to budget constraints.

e) Compare relative genetic gains from selecting early generations, versus advanced lines, for SATs in a) to d). To estimate genetic gains in yield associated with selection for SATs, correlated response to selection was calculated for the same populations based on SATs measured in small (Table 3) and large (Table 4) plots for canopy temperature and CID. Results for POR are also presented (Table 3 - POR). In the majority of cases, the results indicated significant genetic gains. When comparing genetic gains made for RILs versus advanced lines (Tonyp-P) using canopy temperature as a selection criterion (Table 4) there was no consistent difference indicating that CT is as useful a selection criterion for either type of breeding material. Genetic gains were also calculated for visual selections as well as yield itself both measured on small plots (Table 5). However, visual selections cannot be directly compared with yield or SATs as a different selection intensity was used by the breeder, which varied from 51 to 90%, and genetic gains were calculated as the difference between all those included and all those excluded. Nonetheless, a comparison of relative genetic gains across all 5 populations of RILs using different selection criteria in small plots is presented (Table 6). Yield measured on large plots proved to be the best selection criterion giving a gain of 66 g/m2 at selection intensity of 25% while, for SATs measured on small plots, CID of grain (both cycles) and CT in the vegetative period (2003 cycle) also gave gains of over 50 g/m2. Averaged over both cycles and all 5 populations, POR measured during late booting/ear emergence gave similar gain (41 g/m2) to POR measured during grain filling (44 g/m2). Visual selection gave a gain of 40 g/m2.

f) Compare 2 environments contrasting in vapour pressure deficit (VPD) for effectiveness in evaluating SATs.. CT was also measured on the same 5 populations on small plots which had been sown 5 weeks later at the same site to compare the association of CT with yield at a higher vapour pressure deficit. For measurements made during grain-filling, relative humidity was lower and air temperatures higher (Table 3) resulting in a higher VPD. However, the genetic correlations (Table 1) and correlated response (Table 3) did not indicate any advantage of high VPD when measuring CT in predicting yield. Nor were results from Tlaltizapan, a high VPD environment indicative of it being a better selection environment (Table 6).

g) Compare effectiveness of SATs in predicting genetic gains when measured at distinct developmental stages (stem elongation/booting versus grain-filling in the case of CTD and porometry, or when measured on different plant tissues, i.e. leaves versus mature grain in the case of isotope discrimination).

h) Make an economic analysis comparing cost effectiveness of different SATs, in different environments, and using contrasting breeding methodologies. Decision as to whether to pursue such an analysis is pending.

i) Identify iso-morphic sister lines contrasting in SATs for use in Thrust-2. Sets of high and low SATs sisters have been identified based on two years data of CT and POR and one years CID data, from the 5 populations. Up to 6 high and 6 low SATs sisters from 3-5 populations will be sown in 2003/04 for thrust-2 studies.

j) Make available suitable populations for QTL analysis of SATs. See report for 2001/2003

k) Evaluate the use of SATs under Australian conditions. The very dry conditions in SE Australia prevented meaningful evaluation of SATs in the 2002 cycle. There were no rainfall events of any significance beyond the early vegetative stage and supplies of supplementary irrigation water were effectively exhausted by anthesis. Persistent strong, dry winds during the pre-anthesis and post-anthesis phases eliminated significant genetic variance for leaf porosity. Significant variation in leaf-CID was correlated with anthesis dry matter production in the 2 populations of random lines being grown. There was no correlation between leaf-CID and grain yield in either population.
2) Identifying Underlying Physiological and Genetic Mechanisms of SATs.
No new data was collected in 2002/03 but see publications
3) Assessing the Potential of Genetic Sources of Variation in other Physiological Traits.
a) Evaluate new sources of germplasm and elite lines for enhanced expression of a number of traits reflecting variation in source-sink (SS) balance, that may be associated with the expression of SATs and have putative value for yield potential. See report from 2001/03
b) Produce homozygous sister lines from contrasting parents to establish genetic links between SS traits and potential yield gains and establish relationships among SS traits. Progeny of three crosses were evaluated for yield and SS related traits (i) duration of RSG, and (ii) biomass accumulation rate during booting, (iii) partitioning of assimilates to the spike shortly after anthesis The trial had serious stand establishment problems this cycle, so data were generally weaker than in 2002. Nonetheless, duration of RSG was weakly associated with yield in 2 of 3 populations. Biomass accumulation during RSG was associated with yield in 2 of 3 pops. Partitioning of assimilates to the spike at anthesis was associated with yield in 2 of 3 pops. Total biomass at anthesis was associated with yield in 3 pops (Table 7). Canopy temperature measured in the boot and grain-fill stages was positively associated with yield in all 3 populations (Table 2).

Purpose and context of the project. The objective of the project is to evaluate promising new selection criteria to complement traditional selection methodologies for yield in wheat. Wheat is grown on some 220 million ha worldwide, about half of which is in developing countries and CIMMYT has played a major role in increasing the productivity of wheat globally. Nonetheless, demand for wheat is expected to grow by approximately 1.3% per year world-wide and by approximately 1.8% per year in developing countries. Improvement in genetic yield potential since the initial impact of The Green Revolution stands at 0.88% per year and is clearly too low to keep pace with future demand. Given the environmental implications associated with increasing land use, and the cost and complexity of further reducing the relatively small yield gaps in high production areas, improving genetic yield potential of wheat would seem to be a highly cost effective solution for meeting future demands. These facts suggest an urgent need to develop more efficient wheat breeding methodologies to complement existing techniques, as well as to identify new traits which will drive faster yield gains through exploiting the true biological yield potential of the wheat crop. There is now a strong body of evidence emerging indicating that physiological traits have very real potential for improving the efficiency of yield gains in wheat. Research conducted at CIMMYT and in Australia has revealed a consistent correlation between increase in yield potential and changes in stomatal aperture related traits (SATs); i.e stomatal conductance, canopy temperature depression (CTD) and 18O and 13C stable isotope composition.
Names of collaborating researchers and institution
___________________________________________________________________
Researcher Institution
___________________________________________________________________
Mexico:
Dr. M Reynolds, Physiologist CIMMYT
Dr. MvanGinkel Head of Bread Wheat Breeding CIMMYT
Dr. R. Trethowan Bread Wheat Breeder CIMMYT
Dr. Jose Crossa Biometrician CIMMYT
Dr. Prabhu Pingali Economist CIMMYT
Australia:
Dr. A. Condon Physiologist CSIRO
Dr. G. Rebetzke Geneticist CSIRO
Dr. R. Richards Wheat Breeder CSIRO
Prof. G. Farquhar Physiologist ANU
Expected results and value. The technologies developed by this project should significantly improve the efficiency of early generation and advanced line selection, as well as provide a better knowledge base from which to develop more strategic crossing plans, through the identification of yield enhancing traits in new and conventional sources of germplasm. The technologies being developed are equally applicable to collaborating countries and NARS breeding programs. Shifting the wheat yield frontier will have an immediate impact in terms of raising farm level yields as well as in reducing unit production costs. As a consequence domestic food security will be improved and wheat will be available at a lower price thus benefiting the poor consumers, both rural and urban. If this research can improve the rate of increase in genetic yield gains by just one tenth (i.e., from 1.0 to 1.1% p.a.), the annual output will reach 685 m tons by 2020, an extra 15m tons of wheat per year, representing a value of approximately US $ 3 billion p.a. ($200 per ton).
Likely direction of future research activities. Results from this project could be followed up as follows: (i) Develop molecular markers for SATs and other yield enhancing traits to provide additional tools for improving breeding efficiency. (ii) Further exploit the true biological yield potential of wheat in different environments (including marginal environments) based on physiological insights gained from the current work. (iii) Develop capacity
in NARS to fully implement the use of physiological selection criteria in breeding

1) Quantitatively Evaluate Genetic Gains Associated with SATs Using Alternate Selection Methodologies.
a) Quantitatively evaluate genetic gains in early generation breeding populations using SATs as indirect selection criteria in unselected sister lines. SATs (canopy temperature CT, leaf porosity-POR, and carbon isotope discrimination-CID) were measured on 5 populations of random lines grown in small observation plots (1.6 m2) and compared with yields of the same lines in larger plots (6.4 m2). Trials were sown in replicated lattice designs in Obregon, NW Mexico a temperate, irrigated high radiation environment. CANOPY TEMPERATURE/DEPRESSION (CT/D). Canopy temperature was measured between 3-5 times on sunny, relatively windless days during both the booting and grain-filling stages. The genetic correlations between CT/D and yield are presented (Table 1). For the most part correlations were significant. Higher correlations were obtained with CT measured in 2003 than with CTD measured in 2002. Although the result is confounded by year, the trend is consistent with last years results were CTD and CT were measured simultaneously on advanced lines in the trial Tonyp-Padres, and CT was found to show a higher correlation with yield than CTD. Genetic correlations between SATs and yield that were both measured on large plots are presented for 3 populations of RILs and one set of advanced lines pertaining to experiments in Thrust-3 of this project (Table 2); results are very similar. LEAF POROSITY (POR). Leaf porosity was measured using the latest version of the Thermoline viscous-flow porometer. All small observation plots of the 5 populations of random lines were measured twice, once during late-booting/ear-emergence stage and then during grain filling. Because of persistent cloud during February, it was only possible to measure large plots once, around anthesis. Six individual sunlit leaves were sampled in each plot (1.6 m2 and 6.4 m2) at each sampling time, taking about 1 minute/plot before flowering and a little longer during grain filling. The genetic correlations of small-plot POR and large plot yield in 2000/01 and 2001/02 cycles are presented (Table 1- POR). Genetic correlations were moderate-strong in both cycles. Strength of correlations varied among populations, and was strongest for the "7C/Seri" population and weakest for "Cross 5". There was no indication that the correlations were consistently stronger for post-anthesis measurements than for pre-anthesis measurements. CARBON ISOTOPE DISCRIMINATION (CID). Leaf samples were taken during the vegetative stage and grain at maturity from small plots of 4 populations during the 01-02 cycle and analyzed by collaborators at CSIRO in early 2003. The genetic correlations of CID with yield in 2001/02 and 2002/03 cycles are presented (Tables 1 & 2). The correlations are comparable with that of canopy temperature. Samples were also taken from grain of small plots in 5 populations at both sowing dates in the current cycle (2002/03) and have been sent to CSIRO.
b) Quantitatively evaluate genetic gains in F5 breeding populations using SATs as indirect selection criteria on random F4 individual plants in unselected F3:4 bulks. This experiment was not repeated in 2002/03 due to the poor heritability found in previous cycles between POR measurements on single plants with those measured subsequently in yield plots.

c) Semi-quantitatively compare a) with genetic gains realised from SAT-assisted selection on breeder-selected F4 lines. CTD was measured on breeders selected F3:4, and F4:6 plots (modified bulk), derived from 10 elite x elite crosses. Analysis pending results of breeders yield trials which were put on hold in 2002/03 due to budget constraints

d) Semi-quantitatively evaluate the potential complementarity of visual and physiological selection criteria in resoure-use efficient breeding strategy (Selected Bulk). Analysis pending results of breeders yield trials which were put on hold in 2002/03 due to budget constraints.

e) Compare relative genetic gains from selecting early generations, versus advanced lines, for SATs in a) to d). To estimate genetic gains in yield associated with selection for SATs, correlated response to selection was calculated for the same populations based on SATs measured in small (Table 3) and large (Table 4) plots for canopy temperature and CID. Results for POR are also presented (Table 3 - POR). In the majority of cases, the results indicated significant genetic gains. When comparing genetic gains made for RILs versus advanced lines (Tonyp-P) using canopy temperature as a selection criterion (Table 4) there was no consistent difference indicating that CT is as useful a selection criterion for either type of breeding material. Genetic gains were also calculated for visual selections as well as yield itself both measured on small plots (Table 5). However, visual selections cannot be directly compared with yield or SATs as a different selection intensity was used by the breeder, which varied from 51 to 90%, and genetic gains were calculated as the difference between all those included and all those excluded. Nonetheless, a comparison of relative genetic gains across all 5 populations of RILs using different selection criteria in small plots is presented (Table 6). Yield measured on large plots proved to be the best selection criterion giving a gain of 66 g/m2 at selection intensity of 25% while, for SATs measured on small plots, CID of grain (both cycles) and CT in the vegetative period (2003 cycle) also gave gains of over 50 g/m2. Averaged over both cycles and all 5 populations, POR measured during late booting/ear emergence gave similar gain (41 g/m2) to POR measured during grain filling (44 g/m2). Visual selection gave a gain of 40 g/m2.

f) Compare 2 environments contrasting in vapour pressure deficit (VPD) for effectiveness in evaluating SATs.. CT was also measured on the same 5 populations on small plots which had been sown 5 weeks later at the same site to compare the association of CT with yield at a higher vapour pressure deficit. For measurements made during grain-filling, relative humidity was lower and air temperatures higher (Table 3) resulting in a higher VPD. However, the genetic correlations (Table 1) and correlated response (Table 3) did not indicate any advantage of high VPD when measuring CT in predicting yield. Nor were results from Tlaltizapan, a high VPD environment indicative of it being a better selection environment (Table 6).

g) Compare effectiveness of SATs in predicting genetic gains when measured at distinct developmental stages (stem elongation/booting versus grain-filling in the case of CTD and porometry, or when measured on different plant tissues, i.e. leaves versus mature grain in the case of isotope discrimination).

h) Make an economic analysis comparing cost effectiveness of different SATs, in different environments, and using contrasting breeding methodologies. Decision as to whether to pursue such an analysis is pending.

i) Identify iso-morphic sister lines contrasting in SATs for use in Thrust-2. Sets of high and low SATs sisters have been identified based on two years data of CT and POR and one years CID data, from the 5 populations. Up to 6 high and 6 low SATs sisters from 3-5 populations will be sown in 2003/04 for thrust-2 studies.

j) Make available suitable populations for QTL analysis of SATs. See report for 2001/2003

k) Evaluate the use of SATs under Australian conditions. The very dry conditions in SE Australia prevented meaningful evaluation of SATs in the 2002 cycle. There were no rainfall events of any significance beyond the early vegetative stage and supplies of supplementary irrigation water were effectively exhausted by anthesis. Persistent strong, dry winds during the pre-anthesis and post-anthesis phases eliminated significant genetic variance for leaf porosity. Significant variation in leaf-CID was correlated with anthesis dry matter production in the 2 populations of random lines being grown. There was no correlation between leaf-CID and grain yield in either population.
2) Identifying Underlying Physiological and Genetic Mechanisms of SATs.
No new data was collected in 2002/03 but see publications
3) Assessing the Potential of Genetic Sources of Variation in other Physiological Traits.
a) Evaluate new sources of germplasm and elite lines for enhanced expression of a number of traits reflecting variation in source-sink (SS) balance, that may be associated with the expression of SATs and have putative value for yield potential. See report from 2001/03
b) Produce homozygous sister lines from contrasting parents to establish genetic links between SS traits and potential yield gains and establish relationships among SS traits. Progeny of three crosses were evaluated for yield and SS related traits (i) duration of RSG, and (ii) biomass accumulation rate during booting, (iii) partitioning of assimilates to the spike shortly after anthesis The trial had serious stand establishment problems this cycle, so data were generally weaker than in 2002. Nonetheless, duration of RSG was weakly associated with yield in 2 of 3 populations. Biomass accumulation during RSG was associated with yield in 2 of 3 pops. Partitioning of assimilates to the spike at anthesis was associated with yield in 2 of 3 pops. Total biomass at anthesis was associated with yield in 3 pops (Table 7). Canopy temperature measured in the boot and grain-fill stages was positively associated with yield in all 3 populations (Table 2).

1) Quantitatively Evaluate Genetic Gains Associated with SATs Using Alternate Selection Methodologies.
a) Quantitatively evaluate genetic gains in early generation breeding populations using SATs as indirect selection criteria in unselected sister lines. In the 2004 cycle, five populations of random sister lines were grown as small observation plots (1.6 m2) for a quantitative visual assessment of yield (1-10 scale) by a breeder, as well as for a final evaluation of canopy temperature (CT). The same populations were grown by breeders using standard yield trial procedures as a more robust test of how well SATs measured in small plots are associated with yield. Both sets of trials were sown in replicated lattice designs in Obregon, NW Mexico a temperate, irrigated high radiation environment. CANOPY TEMPERATURE/DEPRESSION (CT/D). Canopy temperature was measured between 3-5 times on sunny, relatively windless days during both the booting and grain-filling stages. The genetic correlations between SATs measured on small plots between 2002-2004 and breeders yield in 2004 are presented (Table 1). For the most part correlations were significant. Genetic correlations between SATs and yield that were both measured on large plots are presented for 3 populations of RILs and one set of advanced lines pertaining to experiments in Thrust-3 of this project (Table 2); results are very similar. To estimate genetic gains in yield associated with selection for SATs, correlated response to selection was calculated for the same populations based on SATs measured in small (Table 3) and large (Table 4) plots for canopy temperature and CID. In most cases results indicated significant genetic gains associated with SATs. Genetic gains were also calculated for visual selections on the 1-10 scale (Tables 3). Visual selections on small plots were associated with the highest genetic gains in yield trials for 3 of the 5 populations. Genetic gains were calculated for yield itself measured on small plots. For all populations yield of small plots was associated with larger genetic gains than visual estimates were (Table 5).
b) Quantitatively evaluate genetic gains in F5 breeding populations using SATs as indirect selection criteria on random F4 individual plants in unselected F3:4 bulks. This experiment was discontinued after the 2002 cycle due to the poor heritability found in previous cycles between POR measurements on single plants with those measured subsequently in yield plots.

c) Semi-quantitatively compare a) with genetic gains realised from SAT-assisted selection on breeder-selected F4 lines. CTD was measured on breeders selected F3:4, and F4:6 plots (modified bulk), derived from 10 elite x elite crosses. Analysis pending results of breeders yield trials which were not grown in 2004 cycle due to re-assignment of CIMMYT staff but are planned for the 2005 cycle

d) Semi-quantitatively evaluate the potential complementarity of visual and physiological selection criteria in resoure-use efficient breeding strategy (Selected Bulk). Analysis pending results of breeders yield trials which were not grown in 2004 cycle due to re-assignment of CIMMYT staff but are planned for the 2005 cycle

e) Compare relative genetic gains from selecting early generations, versus advanced lines, for SATs in a) to d). In two trials, one comprising of advanced lines and the other populations of RILs, CT was measured on the same plots as yield was estimated. Genetic correlations between yield and CT (Table 2) and the correlated response of grain yield to selection for CT at 25% selection intensity (Table 4) were similar for the advanced lines as well as the RILS, suggesting that genetic gains in response to selection for SATs are possible with both types of breeding material.

f) Compare 2 environments contrasting in vapour pressure deficit (VPD) for effectiveness in evaluating SATs. In the 2004 cycle CT was measured only in one environment. However, in one trial of advanced lines, TONYP-PADs, CT was compared under different environmental conditions with respect to temperature and other factors (Table 6). It was apparent that CT showed a higher correlation with yield when measured at warmer air temperatures suggesting that higher VPD was associated with a better correlation between CT and yield.

g) Compare effectiveness of SATs in predicting genetic gains when measured at distinct developmental stages (stem elongation/booting versus grain-filling in the case of CTD and porometry, or when measured on different plant tissues, i.e. leaves versus mature grain in the case of isotope discrimination). When comparing genetic correlations of CT in different growth stages with yield it was apparent that grainfilling stage gave slightly larger correlations than booting stage (Tables 1 & 2). For a more comprehensive overview of the effect of growth stage for different SATs, see the 5 year report.

h) Make an economic analysis comparing cost effectiveness of different SATs, in different environments, and using contrasting breeding methodologies. Dr John Brennan, economist spent time in Obregon during the 2004 cycle to make an economic assessment of the cost effectiveness of different SATs (see 5-year report).

i) Identify iso-morphic sister lines contrasting in SATs for use in Thrust-2. Sets of high and low SATs sisters identified from previous cycles were grown in the 2004 cycle (see section 2).

j) Make available suitable populations for QTL analysis of SATs. These can be accessed from F2:3 random bulks where the full genetic diversity from each cross has been maintained using single spike descent from F2 to F3

k) Evaluate the use of SATs under Australian conditions.

2) Identifying Underlying Physiological and Genetic Mechanisms of SATs.
TONYP-PADS. In this trial of genetically diverse advanved lines, CT was compared under different environmental conditions with respect to air temperature, irrigation status of the crop and the previous days cloud cover (Table 6). It was apparent that CT showed a higher correlation with yield when (i) measured after a period continuously sunny weather, at warmer air temperatures, and when soil was drier rather than soon after irrigation. As expected the correlation of CT with yield was higher when measured on still days rather than windy ones. There seemed to be no difference between measuring canopy temperature and canopy temperature depression. These data will be interpreted along with results of a previous trials, in the 5-year report.
NEW Lr19 ISOLINES. Three new pairs of Lr19 (7DL.7Ag) near isolines in the newest high yield backgrounds were evaluated in the 2004 cycle. Two of the three pairs showed significant increases in yield. The yield increases of 7 and 10% were associated with a higher grain number per spike as well as increased spike weight at anthesis (Table 7) as seen in previous experiments. However, in contrast to previous germplasm with this translocation, yield increases were not associated with increased final biomass nor any increased biomass at flowering. Although a single years data, this preliminary result may suggest that the 7Ag translocation has different modes of action depending on genetic background.
SATs ISOLINES
3) Assessing the Potential of Genetic Sources of Variation in other Physiological Traits.
a) Evaluate new sources of germplasm and elite lines for enhanced expression of a number of traits reflecting variation in source-sink (SS) balance, that may be associated with the expression of SATs and have putative value for yield potential.

BIG SPIKE LINES. A set of 24 advanced breeding lines (plus parents and checks) selected for improved sink (big spike trait) and better source:sink balance were studied by a first year PhD student (Table 8). These are the product of a 7-year breeding effort in which initial crosses were made between parental lines with large spikes (sink) and large dark-green leaf canopies (source). Of the 24 sisters, one had higher yield than the standard check Bacanora and10 lines were equal to it. The sisters with the highest yield do not have larger spikes but tend to have higher leaf chlorophyll content.
SPRING x WINTER DOUBLE HAPLOIDS. Double haploids have been produced involving a high biomass UK winter wheat (Rialto) crossed to three "high spike-fertility" spring wheat lines: (i) Bacanora with high grains/m2, (ii) a line with larger than average spike length and acceptable kernel size, (iii) a line with a considerably larger than average spike size. The DH production was executed by CIMMYT (Kazi) and funded by Nottingham University as part of a collaborative project. One set of DH lines will be genetically mapped by Nottingham and at the same time phenotyped in Mexico in the 2005 and 2006 cycles as part of the PhD project mentioned above to improve our physiological and genetic understanding of how spike fertility relates to yield and RUE.
ERECT-LEAF SISTERS. The line Baviacora-98 has among the highest biomass of any bread wheat, a large spike and a very floppy leaf canopy. Based on the idea that a more erect leaf-canopy may increase RUE in a high radiation environment, crosses were made between Baviacora and erect leaf sources. In this cycle, 473 F7 lines from over 10 crosses were evaluated in small (1.6m2) plots for canopy architecture and grain yield as well as height and maturity class. Of these, 116 lines were selected based on agronomic type that also showed a range of canopy architectures to test its association with yield and RUE in subsequent cycles.
MULTI-OVARY. The wheat accession introduced from China showing the multi-ovary (MO) trait was crossed with high yield bread wheats in an effort to improve yield and RUE by increasing spike fertility through increasing grain number per spike. Two breeding strategies were adopted, doubled haploid (DH) production and conventional crossing. In the 2004 cycle we grew for the first time 180 DH lines from 3 crosses of which 78 lines expressed the trait versus 102 that did not. The ratio is close to 1:1 suggesting that the trait is probably controlled by a major gene. While the MO trait was not linked to the tallness of the donor line, it was on average associated with a 35% yield reduction among all progeny.
F4 progeny (1405 lines) from over 25 conventional crosses were also evaluated in small plots. Many of the crosses involved large-spike parents crossed to the MO source with the view to providing a spike architecture that would accommodate the high grain number per spikelet associated with the MO trait. Of these 175 were selected for agronomic type for evaluation in subsequent cycles.

b) Produce homozygous sister lines from contrasting parents to establish genetic links between source:sink (SS) traits and potential yield gains and establish relationships among SS traits. Progeny of three crosses were evaluated for yield and SS related traits (i) duration of rapid spike growth (RSG), (ii) biomass accumulation rate during booting, (iii) partitioning of assimilates to the spike shortly after anthesis. Biomass accumulation during RSG was best associated with yield while the other traits showed weaker associations (Table 9). Canopy temperature measured in the grain-fill stages was positively associated with yield in all 3 populations (Table 2).

1) Quantitatively Evaluate Genetic Gains Associated with SATs Using Alternate Selection Methodologies.
a) Quantitatively evaluate genetic gains in early generation breeding populations using SATs as indirect selection criteria in unselected sister lines.
Results being analysed and to be presented at the 7th Int Wheat Conference in November (Condon et al, 2006)

b) Quantitatively evaluate genetic gains in F5 breeding populations using SATs as indirect selection criteria on random F4 individual plants in unselected F3:4 bulks.

This experiment was discontinued after the 2002 cycle due to the poor heritability found in previous cycles between POR measurements on single plants with those measured subsequently in yield plots.

c) Semi-quantitatively compare a) with genetic gains realised from SAT-assisted selection on breeder-selected F4 lines. CTD was measured on breeders selected F3:4, and F4:6 plots (modified bulk), derived from 10 elite x elite crosses.

Analysis pending results of breeders yield trials grown in 2005 cycle; due to be presented at the Yield Workshop, March 20-24th, 2006, Cd, Obregon..

d) Semi-quantitatively evaluate the potential complementarity of visual and physiological selection criteria in resoure-use efficient breeding strategy (Selected Bulk).

Analysis pending results of breeders yield trials grown in 2005 cycle. Due to be presented at the Yield Workshop, March 20-24th, 2006, Cd, Obregon..

e) Compare relative genetic gains from selecting early generations, versus advanced lines, for SATs in a) to d).

No trials grown in Y04-05 but analysis being continued

f) Compare 2 environments contrasting in vapour pressure deficit (VPD) for effectiveness in evaluating SATs.

As for e)

g) Compare effectiveness of SATs in predicting genetic gains when measured at distinct developmental stages (stem elongation/booting versus grain-filling in the case of CTD and porometry, or when measured on different plant tissues, i.e. leaves versus mature grain in the case of isotope discrimination).

As for e)

h) Make an economic analysis comparing cost effectiveness of different SATs, in different environments, and using contrasting breeding methodologies.

A draft paper has been prepared on the subject by John Brennan.

i) Identify iso-morphic sister lines contrasting in SATs for use in Thrust-2.

(see 2004 report)

j) Make available suitable populations for QTL analysis of SATs. See report for 2001/2003

These can be accessed from F2:3 random bulks where the full genetic diversity from each cross has been maintained using single spike descent from F2 to F3

k) Evaluate the use of SATs under Australian conditions.

2) Identifying Underlying Physiological and Genetic Mechanisms of SATs.
a) Is the association of SATs with yield a function of sink strength, i.e. is high CTD or stomatal conductance caused by large numbers of rapidly filling grain sites leading to demand for high photosynthetic rate, and hence high stomatal conductance, through positive feedback regulation?
b) Do high yield potential lines have a less conservative response to incipient environmental stresses such as rising evaporative demand or drying topsoil, thereby maintaining more stable gas exchange rates when evaporative demand is high or between irrigations?
c) Are good vascular systems, including roots, the key to higher rates of transpiration, or transport of assimilate to the developing florets and grain?
d) Do high yielding lines have intrinsically higher photosynthetic or metabolic potential, permitting favourable growth of the spike before anthesis, and of the grain after anthesis?
e) Are the cooler canopies of high yield potential lines less susceptible to the effects of heat stress on photosynthetic machinery and/or other yield determining processes?

No new trialswere conducted in Y 04-05.

3) Assessing the Potential of Genetic Sources of Variation in other Physiological Traits.
a) Evaluate new sources of germplasm and elite lines for enhanced expression of a number of traits reflecting variation in source-sink (SS) balance, that may be associated with the expression of SATs and have putative value for yield potential
Large spikes - balanacing source and sink. Two sets of germplasm were studied in Y04-05. (i) 24 advanced lines -from crosses between large spike material crossed to lines with large, semi-erect dark green leaves- were evaluated for a second year running. (ii) Three doubled haploid populations were studied for the first time in 2005 involving 3 CIMMYT parents (two novel CIMMYT lines with large spikes -L8 and L14- and one conventional CIMMYT cultivar with large numbers of grains/m2 -Bacanora- crossed with a UK winter wheat cultivar, Rialto. Traits evaluated on both populations included limited growth analysis, above ground biomass and partitioning of assimilates to spike at anthesis, canopy temperature and yield components. Results being analysed and to be presented at the 7th Int Wheat Conference in November (Gaju et al, 2006)
Multi-ovary Of the new germplasm developed including parents with diverse spike architecture, 175 F5 lines (selected from 1400 F4 lines evaluated in 2004) evaluated in 2005.
Erect leaf trait (source) was introgressed from various sources into Baviacora-98, which has high biomass, a large spike and a lax leaf canopy. From the 473 lines grown in 2004 cycle, 116 lines with good agronomic type and a range of canopy architectures were evaluated in 2005.

b) Produce homozygous sister lines from contrasting parents to establish genetic links between source:sink (SS) traits and potential yield gains and establish relationships among SS traits.

A subset of 15 lines selected from previous years were sown to assess the contribution of pre-anthesis assimilates to sink strength. Cloudy weather during boot stage prevented the objectives being accomplished in 2005.

In terms of previous cycles data, advanced path analysis is being used to estimate the contribution of sink related traits to determination of yield and yield components.

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