Proceedings of the Fifth Asian Regional Maize Workshop - Search ...

evaluation are conducted in only one environment, the resultant selected population is environment
specific; i.e., response to selection is realized only for the one specific environment. If
the selected population, or families from the population, are to be grOtm in other environments,
it seems necessary to test in the appropriate environments. Genotype by environment interactions
reduce response to selection because the heritability is reduced. Genotype by environment
interactions are common, and I think they have to be included in selection if the selected
germplasm is expected to be used in a range of environments.
selection of families for intercrossing is based on yield, maturity, and standability. The
heritability estimates from the combined analysis of variance are used as the weighting factors
for each trait and index value based on the sum (or difference) for each family; i.e.,
h1 XL 1- h\XLt.-h'l.3 XL3 - h 1 4 Xl, _ = index value, where XII (grain yield), X12. (grain
moisture), X(3 (root lodging), and X l 4 (stalk lodging) are the family means across environmentr
for family 1.
FROM: C. Chutkaew
Q Could we use the same population size for all traits of selection in breeding program
starting from yield (quantitative) traits to qualitative ones such as protein, oil, agronomic
performance and how big that effective population size?
A The choice of population size for any trait depends on the goals of selection, whether
the trait is quantitative or qualitatively inherited. In most instances in the development of
germplasm for breeding purposes, they are long-term selection programs and population sizes
necessary for the improvement of the more complex traits should be used. The improvement for the
qualitative traits would be realized if they were considered in the selected progenies intermitated,
but at a slower rate than if selection was based only on qualitative traits. If selection
only for a specific qualitative trait and other traits are not considered in the selected
progenies that are intermated, intense selection within larger populations would be appropriate.
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