Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/2/2005
Publication Date: 3/1/2006
Citation: Wu, J., Jenkins, J.N., McCarty Jr., J.C., Saha, S., Stelly, D.M. 2006. An additive-dominance model to determine chromosomal effects in chromosome substitution lines and other germplasms. Theoretical and Applied Genetics. 112:391-399. Interpretive Summary: Chromosome substitution lines are currently available for most of the chromosomes in cotton. When using these lines in cotton improvement programs one needs to separate the genetic effects of the substituted chromosome from the background genetic effects of the remaining chromosomes. Currently there is not a statistical model and analysis software to do this. We have developed a model we call the modified AD model and the software to handle this type of analysis. In addition, our model allows for the chromosome substitution line to be used as a probe to determine the effects of the same numbered chromosome as well as the effect of the remaining 25 chromosomes in cultivars crossed with the substitution line and its recurrent parent. We use parental and F2 data from chromosome substitution line CS-B25 and its recurrent parent crossed with five commercial cultivars to illustrate the analysis and the type of output that can be gained with the statistical model. This new model and analysis software greatly extends the utility of chromosome substitution lines and is amenable to use with any diploid or amphidiploid crop for which chromosome substitution lines are available. This research should be very useful to commercial cotton breeders as it offers them an analytical tool previously not available to them for dissecting the genetic contribution of various cultivars used in crosses with chromosome substitution lines and provides guidance on which cultivars to cross to improve specific useful agronomic and fiber traits.
Technical Abstract: When using chromosome substitution lines in a crop breeding improvement program, one needs to separate the effects of the substituted chromosome from the remaining chromosomes. This cannot be done with the traditional additive-dominance (AD) model where chromosome substitution lines, recurrent parent, and their hybrids are used. In this study, we develop a new genetic model and software, called a modified AD model with genotype x environment interactions, which can predict additive and dominance genetic effects attributed to a substituted alien chromosome in a chromosome substitution line as well as the overall genetic effects of the non-substituted chromosomes. In addition, this model will predict the additive and dominance effects of the same numbered chromosome (i.e. chromosome 25 of cotton in this study) in an inbred line, as well as the effects of the remaining chromosomes in the inbred line. The model requires a chromosome substitution line, its recurrent parent, and their F1 or F2 hybrids between the substitution lines and several inbred lines. Monte Carlo simulation results showed that genetic variance components were estimated with no or slight bias when we considered this modified AD model as random. The correlation coefficient between predicted effects and true effects due to the same numbered chromosomes varied from zero to as high as and greater than 0.90, and it was positively relative to the difference between the CS line and the recurrent line. To illustrate the use of this new genetic model, an upland cotton, Gossypium hirsusum L., chromosome substitution line (CS-B25), TM-1 (the recurrent parent), five elite cultivars, and the F2 hybrids from topcrossing these two lines with the five elite cultivars were grown in two environments in Mississippi. Agronomic and fiber data were collected and analyzed. The results showed that the chromosome substitution line, CS-B25, which has Chromosome 25 from 3-79, G. barbadense substituted into TM-1, had positive genetic associations with several fiber traits. We also determined that Chromosome 25 from FiberMax 966 had significantly positive associations with fiber length and strength; whereas, chromosome 25 from TM-1 and SureGrow 747 had detectable negative genetic effects on fiber strength. The new model will be useful to determine specific chromosome effects in various inbred lines in any diploid or amphidiploid crop for which chromosome substitution lines are available.