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Evaluating Plant Breeding Strategies by Simulating Gene Action and Dryland Environment Effects

^a CSIRO Plant Industry, Long Pocket Lab., 120 Meiers Rd., Indooroopilly, 4068, QLD, Australia
^b School of Land and Food Sci., The University of Queensland, Brisbane, 4072, QLD, Australia
^c Agric. Prod. Syst. Res. Unit, Queensland Dep. of Primary Industries, P.O. Box 102, Toowoomba, QLD, 4350, Australia

View larger version (26K): [in a new window]   Fig. 1. Schematic of the modular structures and linkages between QU-GENE and APSIM used to simulate S1 recurrent selection of sorghum for adaptation to dryland environments. Several other selection strategies that can be simulated as QU-GENE application modules are indicated (e.g., pedigree selection) although the multiple crop and systems modules of APSIM are not. Gene action is defined as expression states that become trait value inputs to APSIM-Sorg, together with soil and weather data. Output from APSIM is processed to define both the yield of all possible genotypes (expression state combinations) and the frequency of drought environment types (ETs) encountered in the target population of environments (TPE). This output comprises the genotype–environment space to which QU-GENE applied S1 recurrent selection to search for superior genotypes. MET, multienvironment trial.

View larger version (26K): [in a new window]   Fig. 2. For the 2000 simulations of cycles of S1 recurrent selection, mean changes in the gene frequency for + alleles associated with four physiological traits—transpiration efficiency (TE, average of five genes), flowering time (PH, three genes), osmotic adjustment (OA, two genes), and stay-green (SG, 5 genes)—given four different selection environments. The selection environments were applied as a multienvironment screen (5 locations by 2 yr) of S1 families consisting of (a, b, and c) the same environment type or (d) the target population of environments in which the three environment types (a, b, and c) were sampled in proportion to represent the target population of environments in the sorghum region of northeastern Australia (Table 2).

View larger version (29K): [in a new window]   Fig. 3. For the same traits and the selection environments given in Fig. 2, mean changes in the gene frequency for + alleles with the constraint that selection was only made among genotypes within one of three maturity types (early, medium, or late). Within each maturity type, genotypes were restricted to three of seven possible expression states in trait PH (Table 1): early (expression states 1–3), intermediate (3–5), or late (5–7). Simulations (captioned in figure) are given for selection environment–constraint combinations that contrast particularly with Fig. 2 (see text).

View larger version (28K): [in a new window]   Fig. 4. For the same traits and selection environments given in Fig. 2, mean yields of successive cycles selected (a, b, and c) within different environment types or (d) by randomly sampling the target population of environments with a specified frequency combination of environments, given no selection constraints or constraining selection to be within one of three genotype maturity groups (see Fig. 3). Scales are varied to emphasize differences within selection environments.

View larger version (28K): [in a new window]   Fig. 5. For the no constraints selection scenario (Fig. 2), the yield of the population when selected under one of four selection environments (env) and then evaluated for the effects of indirect selection in each of the alternate selection environments. TPE, target population of environments.

View larger version (15K): [in a new window]   Fig. 6. For the simulations of S1 recurrent selection, the changes in (a) genotypic, (b) genotype x environment (G x E) interaction variance components, and (c) their ratio for different cycles of selection under the target population of environments (TPE) (Fig. 2) when evaluated in the TPE.

View larger version (16K): [in a new window]   Fig. 7. For the simulations of S1 recurrent selection, the rate of fixation of + alleles for (a) a 15-gene additive model and (b) the 15 additive genes (across four traits) processed through the sorghum crop simulation model. Data in (b) are for the separate gene effects that had been averaged for each trait in Fig. 2d. TPE, target population of environments.