EVALUATION OF DIALLEL ANALYSIS USING BETA-GLUCURONIDASE ACTIVITY FROMTRANSGENES 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 f or the beta-glucuronidase (GUS) activity of six well-defined, homozygo us one-locus tobacco (Nicotiana tabacum L.) transgenic lines, each car rying differently located alleles of the GUS gene, and the nulliplex w ild 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 s ilencing translate well in the diallel parameters of general combining ability (GCA) and specific combining ability (SCA) or more detailed v ersions thereof, when compared to a parsimonious model based on the pr ecise genetic constitution of the transgenic plants lines used as pare nts. The tobacco line with the highest GUS activity also has the highe st GCA, demonstrating that an evaluation of parental phenotype would b e sufficient for determining breeding potential. In case of the epista tic gene silencing, however, there is no positive correlation between GCA and parental performance, the reduction in GUS activity is more se vere than is to be expected on the basis of parental performance.