Optimization of the number of cycles and intensity of selection, and population size in mass selection: Selection for single traits in outcrossing plant populations
K. Yano et al., Optimization of the number of cycles and intensity of selection, and population size in mass selection: Selection for single traits in outcrossing plant populations, BREED SCI, 50(1), 2000, pp. 37-43
Optimum number of cycles and rate of selection and optimum population size
to give the highest cost efficiency in mass selection for allogamous crop p
lants were investigated. The optimum values of these variables were obtaine
d based on the numerical calculations of a new selection efficiency index,
S/C, where S stands for the probability that the desired genetic improvemen
t is achieved in the target population, and C is the cost expended for that
end, Selection procedures that maximize S/C will give the greatest opportu
nity of success under a certain total resource investment. The index S/C wa
s calculated based on Monte Carlo simulations with a model in which the tar
get population was initiated as a hybrid population of two cultivar lines t
hat were genetically fixed for the trait concerned, and populations of a co
nstant size were generated for subsequent selection cycles via random cross
ing between the plants selected with a constant rate in each cycle, The gen
es involved were assumed to be inherited independently and have no epistati
c interaction. The calculations over practically possible ranges of the rel
ated variables led to the following conclusions, If, as would be the case i
n most selection projects for breeding a new commercial variety, the expend
iture of time (years) rather than the resource expense for managing the sel
ection is important, a few to several cycles of selection with a rate of ar
ound 1%, testing a few thousand plants per cycle, should be nearly if not e
xactly the optimum, If the desired improvement is not achieved in these cyc
les, the population should be discarded and a new one should be tested. By
contrast, if the time expenditure is not important, as in the case of the s
election for new breeding stock lines, selection with several or more cycle
s, a rate in the range of 10 to 20% and a population size smaller than 100
should be cost-efficient, Dominance is not an important modifier of the opt
imum values unless the desirable genes are dominant or recessive unidirecti
onally at the majority of the loci involved.