Principles of Plant Genetics and Breeding

192 CHAPTER 11
Table 1 Estimated gain per cycle for grain yield, and ear and plant traits of SP and SA synthetic populations
averaged for 4 years of testing.
In our experiments, selection was carried out for ear size. Each season, 1,000–2,000 haploid plants from an improved synthetic
population were planted in the field. Of these, 200–300 haploids were pollinated by diploid representatives of the same synthetic
population. At harvest time about 20–30 haploids with the largest ears were selected for the next cycle of selection. Three cycles
of haploid sib recurrent selection were completed for two synthetic populations, SP and SA. Initial and improved synthetics were
evaluated in the field for 4 years. The performance results of synthetic SA are presented in the Figure 2. The data indicate that
selection for ear size, utilizing haploids, can result in a significant increase of grain yield.
An important method that effectively estimates the efficiency of a recurrent selection program is the determination of gain per
cycle. This parameter is used for comparing the efficiency of different recurrent selection schemes. Normally gain per cycle for
grain yield in a recurrent selection scheme in maize approximates 2–5% and seldom exceeds 7% (Gardner 1977; Weyhrich et al.
1998). The results obtained by haploid sib recurrent selection are presented in Table 1. For synthetic population SA, the gain per
cycle was 12.0%, and for synthetic SP it was 13.1%. Gain per cycle was distinctly higher than that which is observed when utilizing
conventional recurrent selection methods. The conclusion drawn from the experiment is that the utilization of haploid plants
for the selection of favorable genotypes greatly increases the efficiency of recurrent selection.
Overall, numerous experiments have indicated that haploid generation can be successfully applied to several species on a
large scale. The methods and citations given above provide only a few examples of this useful and efficient method. The utilization
of haploids and doubled haploids can simplify the identification of genotypes that can provide a significant improvement in
a variety of agronomic traits. In addition, haploids and doubled haploids can accelerate the generation of homozygous lines and
pure cultivars. Therefore, haploid-inducement technologies have a bright future in plant breeding.
References
Gain per cycle (%)
SP SA
Traits 1998 1999 2000 2001 Average 1998 1999 2000 2001 Average
Grain yield 11.0 16.4 1.7 17.8 13.1 16.7 21.0 10.3 8.4 12.0
Ear length 9.2 6.6 4.4 7.5 7.8 4.5 9.2 4.4 5.8 6.2
Seeds per row 2.6 6.7 1.1 9.6 6.2 7.5 11.4 4.8 4.8 6.3
Rows number 7.3 6.2 3.0 5.2 2.9 1.4 4.7 3.0 4.4 6.1
Ear diameter 5.7 4.8 0.6 4.1 4.1 3.5 3.7 2.2 2.6 2.0
Plant height 9.3 9.6 10.5 7.7 10.0 12.1 3.7 7.3 4.8 4.8
Ear height 10.0 7.6 10.0 11.8 10.9 16.6 8.4 13.8 11.1 6.7
Leaf length 8.5 6.2 3.8 9.0 7.8 3.3 2.8 1.5 3.2 2.6
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