| | Abstract | Introduction | Materials and methods | Results and discussion | References
Abstract
This study was done to evaluate the application of carbon isotope (13C) discrimination (∆) as a selection criterion for improving water use efficiency (WUE) and productivity of barley on the Canadian prairies. Ten genotypes were subjected to drought at the jointing stage to study the relationship between ∆, WUE and barley productivity. Drought caused considerable reductions in aerial biomass and grain yield of all genotypes examined. Significant genotypic variation was found in WUE. Significant correlations were found between ∆, and WUE as well as ∆ and aerial biomass and grain productivity, which highlight the potential of ∆ (leaves or seeds) as a rapid and reliable method for evaluating WUE and productivity of barley. Genotypes (Manny, Trochu and Seebe) with the highest WUE (low ∆) under drought conditions showed performance comparable to the genotypic average under well-watered conditions. This suggests the potential for improving WUE under drought conditions without yield penalties when conditions are optimum. More research is needed to test this technique under field conditions and to establish a standard protocol that can be used to develop new, improved, water use efficient barley varieties.
Introduction
When pests and diseases are effectively controlled, moisture stress is the major limitation of crop yield across the Canadian prairies. Producers often rely on varieties selected for high yield that are adapted to several environments. Yields, however, do vary within and between locations and years reflecting differences in seasonal distribution and severity of water deficit. In water-limited environments, crop yield is a function of water use, water use efficiency (WUE) and the harvest index (Passioura, 1977). Water use efficiency or water productivity is defined as aerial biomass yield/water use. Crop management or the behavior of various cultivars due to intrinsic differences can influence water use efficiency. Water use efficiency is a trait that has been proposed as a criterion for yield improvement under drought (Rebetzke et al., 2002, Condon and Richard 1992). Breeding for improved WUE has, however been limited for a long time by lack of screening methodology. Farquhar et al. (1982) found that the extent to which C3 plants discriminate against the carbon isotope 13C during carbon assimilation was related to their water use efficiency.
This study was done to evaluate the use of 13C discrimination as a selection tool for identifying water use efficient and drought tolerant barley.
Materials and Methods
Six 6-row and four 2-row barley genotypes were used for the study. The 6-row genotypes were: AC Lacombe, Kasota, Manny, Trochu, Tyto and Vivar. The 2-row cultivars were: CDC Dolly, Niobe, Ponoka and Seebe.
The experiment was performed in a greenhouse with photoperiod of 16 hours using natural light supplemented with sodium halide light bulbs. Day and night temperature ranged from 20 to 32°C and 14 to 20°C, respectively while relative humidity was from 10 to 70% throughout the experiments. Large pots (30 cm tall by 27 cm diameter) were used for the study. The pots were filled with 8 kg of soil mix containing field soil and peatmoss in a 1:3 ratio. All pots were flushed with 4 L of tap water and allowed to drain for two days before seeding. Tensiometers (Irrometer) were installed in selected reference pots to monitore soil water potential. The 10 barley genotypes were compared under two irrigation treatments which were either well-watered (WW) or water stressed (WS). Six seeds of each genotype were planted per pot, which were thinned to 4 seedlings per pot two weeks after emergence. Fertilizer application was done 3 weeks after seeding at 112 kgN/ha, 39 kgP2O5/ha, 85 kgK2O/ha and 13 kgS/ha equivalents. Each genotype was replicated 4 times and all pots were completely randomised. Water stress (drought) was imposed at the jointing stage by withholding irrigation until the soil moisture content was approximately 10 volume% compared to 30 volume% of the well watered treatments. These moisture levels were then maintained until grain maturity. A 2cm layer of perlite was put on each pot to reduce surface evaporation. Water use was monitored by weighing the pots regularly and replacing the amount of water lost.
At the heading stage, leaf laminas of plants of each genotype were harvested and dried at 70°C for 48 hours. Dried samples were ground to pass a 1-mm sieve and the carbon isotope composition of each cultivar was determined by mass spectrometry. At maturity, plants were harvested and aerial biomass, grain yield and its components were assessed. Seeds of each genotype were sampled and processed for determination of carbon isotope composition.
Data were analyzed using SAS, version 10.0 (SAS Institute, Cary, NC) software. A linear correlation analysis was used to examine the mean genotypic relationships between traits using the CORR procedure.
Results and Discussion
Among the 6-row barley genotypes, significant differences were observed within each irrigation treatment in WUE and 13C discrimination. For ∆-seeds and ∆-leaves, extreme cultivars differed by 1.72 and 1.91, respectively, under drought and by 1.61 and 1.22, respectively, under well-watered conditions (data not shown). Among the 2-row genotypes, no significant differences were found in WUE, but 13C discrimination (∆-seeds and ∆-leaves) was significantly different under both watering conditions. For ∆-seeds and ∆-leaves, extreme cultivars differed by 2.35 and 1.27, respectively, under drought and by 0.94 and 1.15, respectively under well-watered conditions (data not shown).
Among the 6-row barley genotypes, WUEDM was strongly correlated with both ∆-seeds and ∆-leaves under drought (Figs. 1 & 2). Aerial dry matter production (DM) and grain yield were also strongly correlated with ∆-seeds (Figs. 3 & 4). Similar correlations were observed among the 2-row barley cultivars under drought, except grain yield and ∆-seeds, which showed no relationship (Figures not shown).
Figure 1. Relationship between 13C discrimination of seeds and WUE (based on dry matter/water use) of 6-row barley under water stress.
Figure 2. Relationship between 13C discrimination of leaves and WUE (based on dry matter/water use) of 6-row barley under water stress.
Figure 3. Relationship between 13C discrimination of seeds and aerial dry matter of 6-row barley under water stress.
Figure 4. Relationship between 13C discrimination of seeds and grain yield of 6-row barley under water stress.
The relationship between ∆ and WUE have been studied extensively in several species and the 2 traits have been reported to be negatively associated (Farquhar and Richards 1984, Condon et al., 1990, Read et al., 1991, Ebdon et al., 1998, Teulat et al., 2001, Rebetzke et al., 2002). High correlations have been reported between ∆ and aerial biomass or grain yield (Johnson and Bassett, 1991; Acevedo, 1993; Condon and Richards, 1993; Teulat , 2001).
Variation in ∆ in cereals is known to arise from variation in photosynthetic capacity as well as stomatal conductance (Condon et al., 1990; Morgan and LeCain, 1991). Some studies have shown that when stomatal conductance is the main source of variation in WUE and when water supply does not impose a major limitation on crop growth, a high WUE may be disadvantageous (Condon et al., 2002). A review by Condon et al., (2002) suggests that improved WUE may be useful in stored-moisture environments where within-season rainfall makes up a relatively small proportion of the total water available for growth.
Results obtained in the present study indicate that significant variation exists in WUE amongst the barley genotypes examined. The strong correlations between ∆ and aerial biomass highlight the potential of ∆ as a measure of productivity in barley subjected to drought in a greenhouse. There is a need to screen more genotypes and to verify the usefulness of ∆ (leaves or seeds) in breeding programs under field conditions.
References
Acevedo, E. 1993. Potential of carbon isotope discrimination as a selection criterion in barley breeding. p. 399–417. In J.R. Ehleringer et al. (ed.) Stable Isotopes and Plant Carbon-Water Relations. Academic Press, San Diego, CA.
Condon, A.G. and R.A. Richards 1992. Broad sense heritability and genotype x environment interaction for carbon isotope discrimination in field-grown wheat. Aust. J. Agric. Res. 43:921–934.
Condon, A.G., and R.A. Richards, 1993. Exploiting genetic variation in transpiration efficiency in wheat: An agronomic view. p. 435–450. In J.R. Ehleringer et al. (ed.) Stable Isotopes and Plant Carbon-Water Relations. Academic Press, San Diego, CA.
Condon, A.G., G.D. Farquhar, and R.A. Richards 1990. Genotypic variation in carbon isotope discrimination and transpiration efficiency in wheat. Leaf gas exchange and whole plant studies. Aust. J. Plant Physiol. 17:9–22.
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Farquhar, G.D., and R.A. Richards 1984. Isotopic composition of plant carbon correlates with water-use efficiency of wheat genotypes. Aust. J. Plant Physiol. 11: 539–552.
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Johnson, D. A., and L. M. Bassett 1991: carbon isotope discrimination and water use efficiency in four cold season grasses. Crop Sci. 31, 457-463.
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Passioura, J.B. 1977. Grain yield, harvest index, and water use of wheat. J. Aust. Inst. Agric. Sci. 43: 117–120.
Read, J.J., D.A. Johnson, K.H. Asay and., L. L. Tieszen 1991. Carbon isotope discrimination, gas exchange, and water-use efficiency in crested wheat grass clones. Crop Sci. 31, 1203-1208.
Rebetzke, G.J., A.G. Condon, R.A. Richards, and G.J. Farquhar 2002. Selection for reduced carbon-isotope discrimination increases aerial biomass and grain yield of rainfed bread wheat. Crop Sci.42: 739-745.
Teulat B., O. Merah and D. This 2001. Carbon isotope discrimination and productivity in field grown barley genotypes. J. Agron. Crop Sci. 187: 33-39.
Anyia, A.O. (1), Archambault, D.J. (1), Slaski, J.J. (1), and Nyachiro, J.M. (2)
(1) Environmental Technologies, Alberta Research Council Inc., P.O. Bag 4000, Vegreville, Alberta, T9C 1T4
(2) Field Crop Development Centre, Alberta Agriculture Food and Rural Development, Lacombe, Alberta, T4L 1W8
Presented at the 18th North American Barley Researchers Workshop, July 17-20, 2005 |
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