Comparison of Two Breeding Strategies by Computer Simulation Jiankang Wang,* Maarten van Ginkel, Dean Podlich, Guoyou Ye, Richard Trethowan, Wolfgang Pfeiffer, Ian H. DeLacy, Mark Cooper, and Sanjaya Rajaram ABSTRACT pedigree/bulk method (MODPED) (van Ginkel et al., 2002), which successfully produced many of the widely Breeding strategies used by plant breeders are many and varied, adapted wheats now being grown in the developing making it difficult to compare efficiencies of different breeding strate- world. This method was replaced in the late 1990s by gies through field experimentation. The objective of this paper was to compare, through computer simulation, two widely used breeding the selected bulk method (SELBLK) (van Ginkel et al., strategies, the modified pedigree/bulk selection method (MODPED) 2002) in an attempt to improve resource-use efficiency. and the selected bulk selection method (SELBLK), in CIMMYT’s The major differences between MODPED and SELBLK wheat breeding program. The genetic models developed accounted are outlined below. for epistasis, pleiotropy, and genotype  environment (GE) interac- The MODPED method begins with pedigree selec- tion. The simulation experiment comprised the same 1000 crosses, tion of individual plants in the F2 followed by three developed from 200 parents, for both breeding strategies. A total of bulk selections from F3 to F5, and pedigree selection 258 advanced lines remained following 10 generations of selection. in the F6, hence the name modified pedigree/bulk. In The two strategies were each applied 500 times on 12 GE systems. the SELBLK method, spikes of selected F2 plants within Findings indicated that genetic gain from SELBLK was on average one cross are harvested in bulk and threshed together, 3.9% higher than that from MODPED, and genetic gain adjusted by target genotypes from SELBLK was on average 3.3% higher than resulting in one F3 seed lot per cross. This selected bulk MODPED for a wide range of genetic models. A greater proportion selection is also used from F3 to F5, while pedigree of crosses were retained (25% more) by means of SELBLK compared selection is used only in the F6. A major advantage of with MODPED, and from F1 to F8, SELBLK required one third less SELBLK compared with MODPED is that fewer seed land than MODPED and produced fewer families (40% of the number lots need to be harvested, threshed, and visually selected for MODPED). For the genetic models considered in our study, for seed appearance. In addition, significant savings in computer simulations showed that the SELBLK method resulted in time, labor, and costs associated with nursery prepara- slightly greater genetic gain and significant improvements in cost effec- tion, planting and plot labeling ensue, and potential tiveness. sources of error are avoided (van Ginkel et al., 2002). Although some small-scale field experiments have been conducted comparing the efficiencies of these breeding T he global impact of the wheat breeding program strategies (Singh et al., 1998), the efficiency of SELBLK of the International Maize and Wheat Improvement compared with that of MODPED remains untested on Center (CIMMYT) has been significant and well docu- a larger scale. mented (Rajaram, 1999). Many factors have contributed Quantitative genetics provides much of the frame- to CIMMYT’s success, such as breeding targeted to work for the design and analysis of selection methods megaenvironments (MEs), use of a diverse gene pool used within breeding programs (Allard, 1960; Falconer for crossing, and shuttle breeding (Rajaram et al., 1994; and Mackay, 1996; Cooper et al., 1999). However, there Rajaram, 1999). Another key factor, however, has been are usually associated assumptions, some of which can the breeding strategies adopted by CIMMYT breeders. be easily tested or satisfied by experimentation; others A breeding strategy is defined as all crossing, seed prop- can seldom, if ever, be met. Computer simulation pro- agation, and selection activities in an entire breeding vides us with a tool to investigate the implications of cycle. A breeding cycle begins with crossing and ends relaxing some of the assumptions and the effect this has at the generation when the selected advanced lines are on the conduct of a breeding program. QU-GENE, a returned to the crossing block as new parents. simulation platform for quantitative analysis of genetic The strategies used by CIMMYT breeders have models, was developed for this purpose (Podlich and evolved with time. Pedigree selection was used primarily Cooper, 1998). It has been used to compare efficiencies from 1944 until 1985. From 1985 until the second half of different breeding strategies (Cooper et al., 2002) and of the 1990s, the main selection method was a modified modifications to existing selection strategies (Podlich et Abbreviations: B, CIMMYT’s breeding location at El Batan, Mexico; J. Wang, M. van Ginkel, R. Trethowan, W. Pfeiffer, S. Rajaram, CIMMYT, Centro Internacional de Mejoramiento de Maiz y Trigo Wheat Program, CIMMYT, Apdo. Postal 6-641, 06600 Mexico, D.F., (International Maize and Wheat Improvement Center); GE, geno- Mexico; D. Podlich and M. Cooper, Pioneer Hi-Bred International type  environment; LR, leaf rust; ME, megaenvironment; ME1, Inc., 7300 N.W. 62nd Avenue, PO Box 1004, Johnston, IA 50131, the low rainfall and irrigated environment type for spring wheat; USA; G. Ye and I.H. DeLacy, School of Land and Food Sciences, MODPED, modified pedigree/bulk selection method; QUCIM, a QU- The University of Queensland, Brisbane, Qld 4072, Australia. This GENE application breeding simulation module; QU-GENE, a simula- project was supported in part by the Grains Research and Develop- tion platform for quantitative analysis of genetic models developed ment Corporation (GRDC) of Australia. Received 30 May 2002. by The University of Queensland, Australia; QUGENE, the engine *Corresponding author (jkwang@cgiar.org). of the QU-GENE; SELBLK, selected bulk selection method; SP, small plot; T, CIMMYT’s breeding location at Toluca, Mexico; TG, Published in Crop Sci. 43:1764–1773 (2003).  Crop Science Society of America target genotype; TPE, target population of environments; YR, yellow rust; YT, yield trial. 677 S. Segoe Rd., Madison, WI 53711 USA 1764