A testcross procedure for selecting exotic strains to improve pure-line cultivars in predominantly self-fertilizing species |
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Authors: | S K St Martin K S Lewers R G Palmer B R Hedges |
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Institution: | (1) Department of Horticulture and Crop Science, Ohio Agric. Res. and Development Center (OARDC), Ohio State University, 2021 Coffey Rd, 43210 Columbus, OH, USA;(2) Department of Agronomy, Iowa State Univ., 50011 Ames, IA, USA;(3) USDA-ARS, Department of Agronomy, and Dep. of Zoology/Genetics, Iowa State University, 50011 Ames, IA, USA;(4) Agriculture and Agri-Food Canada, Harrow Research Station, NOR 1GO Harrow, Ontario, Canada |
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Abstract: | Methods for identifying germplasm carrying alleles with the potential to improve a particular single-cross hybrid have been proposed and discussed in recent years. There is a need for similar methods to be used in breeding crops for which pure-line cultivars, rather than hybrids, are the goal. The objective of this research was to develop a method to identify germplasm lines with the potential to contribute favorable alleles not present in a specified pure line or set of pure lines. Given a set of adapted pure lines (A
1, A
2 ..., A
m) to be improved and a set of germplasm lines (P
1
P
2 ..., P
f), the procedure consists of producing all f x m possible hybrids and evaluating them along with the parents. The testcross statistic T
ij is defined by T
ij=(F
ij–A
j)+(1–) (F
ij–P
i), where A
j, P
i, and F
ij represent the performance of thej
th adapted line, the i
th germplasm line, and their hybrid, respectively. The statistic
is the mean value of T
ij over all adapted parents A
j. If =(1/2)(1+d), where d = the mean degree of dominance, then T
ij measures the potential for alleles from P
i to improve A
j and
measures the potential for alleles from P
i to improve the set A
1, A
2 ..., A
m. Use of data on soybean and peanut hybrids published by other researchers suggests that the value assumed for d has little effect on the P
i chosen. The ability of the T
ij and
statistics to identify germplasm strains carrying rare favorable alleles should be assessed in empirical studies.Joint contribution: OARDC (Journal Articale No. 161-94), USDAARS, Iowa Agriculture and Home Economics Expriment Station (Journal Paper No. J-16109; Project 2985), and Agreculture and Agri-Food Canada. Salaries and research support for S. K. St. Martin Provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, Ohio State University |
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Keywords: | Exotic germplasm Selection of parents Testcross |
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