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A testcross procedure for selecting exotic strains to improve pure-line cultivars in predominantly self-fertilizing species

St Martin, S.K., Lewers, K.S., Palmer, R.G., Hedges, B.R.
Theoretical and applied genetics 1996 v.92 no.1 pp. 78-82
crops, plant breeding, germplasm, crossing, inbred lines, cultivars, lines, genetic improvement, statistical analysis, Glycine max, Arachis hypogaea, experimental design
Methods for identifying germplasm carrying alleles with the potential to improve a particular singlecross 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 (A1, A2,...,Am) to be improved and a set of germplasm lines (P1,P2,...,Pf), the procedure consists of producing all f X m possible hybrids and evaluating them along with the parents. The testcross statistic Tij is defined by Tij = gamma(Fij-Aj)+(1-gamma) (Fij-Pi), where Aj, Pi, and Fij represent the performance of the jth adapted line, the ith germplasm line, and their hybrid, respectively. The statistic mean = (1/m)sigma(Tij) is the mean value of Tij over all adapted parents Aj. If gamma = (1/2)(1+d'), where d' = the mean degree of dominance, then Tij measures the potential for alleles from Pi to improve Aj, and mean Ti measures the potential for alleles from Pi to improve the set A1, A2,...,Am. Use of data on soybean and peanut hybrids published by other researchers suggests that the value assumed for d' has little effect on the Pi chosen. The ability of the Tij and mean Ti statistics to identify germplasm strains carrying rare favorable alleles should be assessed in empirical studies.