Genotypic Variation in Carbon Isotope Discrimination and Transpiration Efficiency in Wheat. Leaf Gas Exchange and Whole Plant Studies

1990 ◽  
Vol 17 (1) ◽  
pp. 9 ◽  
Author(s):  
AG Condon ◽  
GD Farquhar ◽  
RA Richards
Keyword(s):  
Boundary Layer ◽  
Water Loss ◽  
Dry Matter ◽  
Carbon Isotope Discrimination ◽  
Genotypic Variation ◽  
Transpiration Efficiency ◽  
Layer Resistance ◽  
Boundary Layer Resistance ◽  
The Relationship ◽  
Canopy Water

The relationship between carbon isotope discrimination, Δ, measured in plant dry matter and the ratio of intercellular to atmospheric partial pressures of CO2, pi/pa, in leaves was examined in two glasshouse experiments using 14 wheat genotypes selected on the basis of variation in Δ of dry matter. Genotypic variation in Δ was similar in both experiments, with an average range of 1.8 x 10-3. Variation in pi/pa was significant but the range in pi/pa was relatively small, averaging 0.075. In both experiments, Δ measured in dry matter and pi/pa measured in flag leaves were positively correlated. Variation among genotypes in pi/pa was attributed, approximately equally, to variation in leaf conductance and in photosynthetic capacity. The relationship between plant transpiration efficiency, W* (the amount of above-ground dry matter produced per unit water transpired) and � was also examined. There was a negative correlation between W * and Δ; under well watered conditions and under gradually increasing terminal water stress. The relationship between W* of stressed plants and Δ measured in well watered plants was also negative. These results indicate that genotypic variation in Δ measured in dry matter should provide a reasonable measure of genotypic variation in long-term mean leaf pi/pa in wheat. Further, selection for improved plant transpiration efficiency in wheat under both well watered and terminally water- stressed conditions should be possible based on Δ measured in well watered plants. The extent to which such selection will be effective in improving transpiration efficiency at the field canopy level may depend on the influence of boundary layer resistance on transpirationsal water loss. Under well watered conditions and at full canopy closure, the influence of boundary layer resistance on canopy water loss may be relatively large and stomatal control of water loss may be limited. Under water stress, stomatal control of canopy water loss will be greater.

Relationships between carbon isotope discrimination, water use efficiency and transpiration efficiency for dryland wheat

1993 ◽  
Vol 44 (8) ◽  
pp. 1693 ◽  
Author(s):  
AG Condon ◽  
RA Richards ◽  
GD Farquhar
Keyword(s):  
Water Use Efficiency ◽  
Soil Water ◽  
Water Use ◽  
Negative Correlation ◽  
Seasonal Changes ◽  
Dry Matter ◽  
Carbon Isotope Discrimination ◽  
Transpiration Efficiency ◽  
Use Efficiency ◽  
The Relationship

Carbon isotope discrimination (-) has been shown to be negatively correlated with water use efficiency for wheat cultivars grown in the glasshouse. In the field this negative correlation has been confirmed for peanut but it has yet to be confirmed for wheat. Indeed, several field studies on wheat have shown positive (rather than negative) relationships between dry matter production and -. The aim of this study was to determine the relationship between - and water use efficiency for wheat grown in a dryland environment characterized by winterlspring-dominant rainfall and terminal drought. Eight genotypes chosen to give a range in - of c. 2.0x10-3 were grown on a red earth at Moombooldool in the Riverina region of New South Wales. Water use and above-ground dry matter (DM) were measured over the course of the season. Water use was partitioned into transpiration and soil evaporation and values of crop water use efficiency (WET) and transpiration efficiency ( WT) calculated. To account for the effect on WT of seasonal changes in the vapour pressure deficit of the air (D), crop coefficients (k) were derived by multiplying WT by the transpiration-weighted average daytime value of D for each genotype. During the preanthesis period, when there was little limitation of soil water supply on growth, there was a positive relationship between DM and -, as observed previously. The relationship between WET and - also had a positive (though non-significant) trend, but the relationship between k and - was negative, i.e. once the effects of variation in the ratio T/ET and seasonal changes in D were accounted for, the negative correlation between water use efficiency and - re-emerged. This apparent conflict between WET and k arose because genotypes with high - values developed their leaf area faster, with two important consequences. First, high - genotypes transpired more of their water supply during the winter when D was low and the exchange of water for CO2 more efficient. Second, transpiration made up a greater proportion of total water use by high - genotypes. The relationship between water use efficiency and - was further complicated as the crops depleted the soil water store after anthesis. During this period DM production tended to be greater in low - genotypes that had conserved soil water in the preanthesis period. However, DM production also remained high for two high - genotypes. The cause of this variation in post-anthesis growth among high - genotypes was not established.

Genetic variation for leaf carbon isotope discrimination and its association with transpiration efficiency in canola (Brassica napus)

2020 ◽  
Vol 47 (4) ◽  
pp. 355
Author(s):  
Shek M. Hossain ◽  
Josette Masle ◽  
Andrew Easton ◽  
Malcolm N. Hunter ◽  
Ian D. Godwin ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Carbon Isotope ◽  
Carbon Isotope Discrimination ◽  
Genotypic Variation ◽  
Dry Weight ◽  
Transpiration Efficiency ◽  
Isotope Discrimination ◽  
Leaf Chlorophyll ◽  
Total Dry Weight ◽  
Positive Correlations

Drought is a major constraint to canola production around the world. There is potential for improving crop performance in dry environments by selecting for transpiration efficiency (TE). In this work we investigated TE by studying its genetic association with carbon isotope discrimination (Δ) and other traits, e.g. specific leaf weight (SLW) and leaf chlorophyll content (SPAD). Among the 106 canola genotypes – including open-pollinated, hybrid, inbred types and cytoplasmic variants – tested in the field and glasshouse there was significant genotypic variation for TE, Δ, plant total dry weight, SLW and SPAD. Strong negative correlations were observed between TE and Δ (–0.52 to –0.76). Negative correlations between Δ and SLW or SPAD (–0.43 to –0.78) and smaller but significant positive correlations between TE and SLW or SPAD (0.23 to 0.30) suggested that photosynthetic capacity was, in part, underpinning the variation in TE. A cytoplasmic contribution to genetic variation in TE or Δ in canola was also observed with Triazine tolerant types having low TE and high Δ. This study showed that Δ has great potential for selecting canola germplasm with improved TE.

Broad sense heritability and genotype × environment interaction for carbon isotope discrimination in field-grown wheat

1992 ◽  
Vol 43 (5) ◽  
pp. 921 ◽  
Author(s):  
AG Condon ◽  
RA Richards
Keyword(s):  
Carbon Isotope ◽  
Dry Matter ◽  
Carbon Isotope Discrimination ◽  
Genotypic Variation ◽  
Broad Sense ◽  
Environment Interaction ◽  
Broad Sense Heritability ◽  
Isotope Discrimination ◽  
Average Value ◽  
Plant Parts

Carbon isotope discrimination (-) has been proposed as a possible selection criterion for greater water use efficiency in breeding programs for water-limited environments because it provides an integrative assessment of genotypic variation in leaf transpiration efficiency. Considerable genotypic variation for - has been demonstrated in wheat, but environmental factors may cause even larger changes in the value of - measured in plant dry matter, which could compromise the effective use of - in breeding programs. In this study we assess broad-sense heritability of - and the significance of genotype x environment interaction for - in field-grown wheat. Another objective was to identify the most effective growth stage or plant part to characterize genotypic variation in -. Experiments were done using several large sets of genotypes (between 8 and 40, usually c. 20) grown in a range of field environments spanning the southern Australian wheat-belt. Carbon isotope discrimination was determined on unreplicated grain samples from seven Interstate Wheat Variety trials grown in 1983 and 1984 and on several plant parts taken from replicated experiments conducted at four locations in south-west New South Wales from 1985 to 1988. From these replicated experiments broad-sense heritabilities for - were calculated on a genotype mean basis h2-M) and on a single-plot basis (h2-P). In dry matter sampled from several environments, site-mean - ranged from 21.0 x 10-3 to 18.9 x 10-3 for early-formed dry matter and from 16.4 x 10-3 to 13.4 x 10-3 for grain. When followed in a single environment, the value of - fell from c. 20 x 10-3 in early-formed leaves to 15.4 x 10-3 in the grain. Variation among genotypes in - of different plant parts was always significant, and was typically c. 2 x 10-3 . Among Australian wheats, low values of - (implying greater transpiration efficiency) were strongly associated with the WW15 genetic background. Estimates of broad-sense heritability for - averaged over 95%, on a genotype mean basis, in experiments where common genotypes were grown in numerous environments. In individual trials, heritability was lowest for plant material sampled near anthesis (average value for h2-M, 83% and for h2-p, 62%) and greatest for dry matter laid down before or during early stem elongation (average value for h2-M, 95% and for h2-P 88%). Even though heritability for grain - was also relatively high (average value for h2-M, 92% and for h2-P, 79%), genotypic differences in grain - are difficult to interpret because of the likelihood of some changes in genotype ranking for - resulting from differences among genotypes in the degree of water stress encountered during grain filling. As well, the contribution of remobilized carbon to grain - may vary between environments and genotypes. We conclude that, for wheat, assessment of genotypic variation in - should be most effective under well-watered conditions using dry matter laid down early in plant development.

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