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Improving Intrinsic Water-Use Efficiency and Crop Yield

^a CSIRO Plant Industry, GPO Box 1600, Canberra, ACT, 2601, Australia
^b Environmental Biology, Australian National Univ., Canberra, ACT, 2601, Australia

View larger version (22K): [in a new window]   Fig. 1. A schematic illustrating the dependence of ci on the relationship between stomatal conductance and photosynthetic capacity. In this "A/ci" plot, the two curved lines rising from near the origin represent the dependence of A on ci as determined by leaf gas-exchange measurements taken over a range of external CO2 concentrations. Variation in the initial slope of these curves reflects variation in photosynthetic capacity. The two curved lines are intersected by two straight lines originating at the ambient CO2 concentration, ca. The slope of these straight lines is the stomatal conductance to CO2, gc. The intersections indicated by numerals represent the "operating" values of ci (and of A, gc, and ci/ca) for three genotypes of a C3 species. The data shown here were derived from leaf gas-exchange measurements on three wheat varieties reported in Condon et al. (1990). (Adapted from Condon and Hall, 1997.)

View larger version (25K): [in a new window]   Fig. 2. Patterns of soil water extraction at two locations under two wheat genotypes, Quarrion and Matong, that differ in WT because of a large difference in g.

View larger version (36K): [in a new window]   Fig. 3. Associations between yield and 13C among wheat breeding lines grown under rain-fed conditions at Condobolin, eastern Australia, in 1992 and 1993. The breeding lines were F6 (1992) and F7 (1993) progeny of two crosses between parents with low and high values of 13C (Rosella x Matong and Quarrion x Cranbrook). The values of 13C plotted are genotype means for leaf material of F5 lines sampled early in the 1991 season when there was no water stress. Least-squares linear fits are plotted where correlation coefficients were statistically significant (P < 0.05, n = 30). Among the lines within each cross there was only small variation for either flowering date or height but lines from the Rosella x Matong cross on average flowered one week later than the lines from the Quarrion x Cranbrook cross. (Adapted from Condon and Hall, 1997.)

View larger version (19K): [in a new window]   Fig. 4. Relationships between final grain yield and above-ground dry matter production for the periods from (a) sowing to anthesis and (b) anthesis to physiological maturity, for a collection of wheat genotypes grown under rain-fed conditions at Moombooldool, south-eastern Australia, in 1986. (Adapted from Condon and Hall, 1997.)

View larger version (28K): [in a new window]   Fig. 5. Average simulated yield impact for two locations in eastern Australian of breeding to improve WT, early vigor and a combination of WT and early vigor in spring wheat. Simulations were done with the SIMTAG wheat crop growth model and 25–30 years of historical weather data for each location (Condon and Stapper, 1995, unpublished).

View larger version (20K): [in a new window]   Fig. 6. Average yield differential between backcross breeding lines of wheat selected for either high WT (low 13C) or low WT (high 13C). Average yield differential calculated for each location as [(mean yield low 13C) – (mean yield high 13C)]/[mean yield high 13C].

View larger version (14K): [in a new window]   Fig. 7. The relationship between grain yield and 13C of grain for advanced breeding lines of rice grown under flood-irrigation at Yanco, south-eastern Australia, 1992 (Condon and Lewin, 1993, unpublished).