Evaluation of diallel analysis using β-glucuronidase activity from transgenes in Nicotiana tabacum

A full diallel analysis is a tool for selection in plant breeding that has been subject to many discussions and controversies regarding its interpretation and merits. The analysis of well-defined transgenes by such an approach permits assessment of the value of diallel analyses. The performance of the Eberhart/Gardner diallel approach is analysed for the β-glucuronidase (GUS) activity of six well-defined, homozygous one-locus tobacco (Nicotiana tabacum L.) transgenic lines, each carrying differently located alleles of the GUS gene, and the nulliplex wild type. Tobacco is an inbreeding plant species, therefore all these lines are fully isogenic apart from the T-DNA insertion. The analysis shows that additivity of GUS gene activity as well as epistatic gene silencing translate well in the diallel parameters of general combining ability (GCA) and specific combining ability (SCA) or more detailed versions thereof, when compared to a parsimonious model based on the precise genetic constitution of the transgenic plants lines used as parents. The tobacco line with the highest GUS activity also has the highest GCA, demonstrating that an evaluation of parental phenotype would be sufficient for determining breeding potential. In case of the epistatic gene silencing, however, there is no positive correlation between GCA and parental performance, the reduction in GUS activity is more severe than is to be expected on the basis of parental performance.