Minimising inter-laboratory variation when constructing a unified molecular database of plant varieties in an allogamous crop.

The construction of large-scale databases of molecular profiles of plant varieties for variety identification and diversity analyses is of considerable interest. When varieties of an allogamous species such as oilseed rape are analysed and described using molecular markers such as microsatellites, care is needed to represent the variety in a meaningful yet useful way. It is possible to characterise such heterogeneous genotypes by analysing bulked samples comprising more than one individual seed or plant, but this approach may result in complex microsatellite profiles. Intuitively it would be reasonable to represent a variety by the common 'major alleles' in a profile, but how to define these 'major alleles' remains problematic. This paper describes methods of analysing DNA microsatellite data that will allow independent and objective data production at a number of laboratories. Methods for establishing allele scoring rules (thresholding) are described and the effect of these rules on the utility of the data is discussed.