14 I EUROPEAN SEED I EUROPEAN-SEED.COM I n plant breeding, molecular techniques are used to screen thousands of lines before they even get to the glasshouse or field. This can remove breeding lines that do not express spe- cific breeding aims, such as disease resistance, without having grown them. This advance in breeding techniques has allowed faster and more targeted variety improvement. This efficiency has resulted in a larger number of varieties being submitted for DUS (Distinctness, Uniformity and Stability) testing for PBR (Plant Breeder’s Rights) and/or National Listing in the case of agricultural crops. The DUS system must adapt to be able to cope with this increase effectively, whilst maintaining the standards already in place. WHAT ARE THE DUS ISSUES? One of the most significant difficulties with the DUS test- ing system is the increasing size of the reference collections. Relevant new varieties granted PBR or added to a National List are added to the reference collection for the trial(s), which follow. Testing Authorities have developed various approaches to this situation – e.g. cyclic planting in out-breeding crops or database management – for screening self-pollinating and clon- ally propagated crops. However, with increasing collections, the systems in place are themselves becoming difficult to manage. This is a particular problem in crops where the parental lines of hybrids are also evaluated within the DUS test – for each and every hybrid variety there can be between three and five paren- tal lines added to the test. The increasing size of the DUS refer- ence collection is resulting in a testing system that is becoming unsustainable. The question of maintaining a reference collection is also raised in truly international crops, where the same varieties are sold worldwide. The difficulties arise when transferring plant material from one country to another while maintaining phy- tosanitary standards. Also, the logistics of moving live plant material can be troublesome – there is no guarantee that the samples will arrive in a condition ready for trial. Another issue in the compilation of a reference collection is locating plant material on the open market that is of an appropri- ate growth stage; again, this is a particular problem in ornamen- tal crops. Using plant material from a range of sources means that the effect of initial growing conditions on the morphology of the plants must be considered. For example, tissue culture production or simply the age of the material can affect certain characteristics, not to mention the extreme effect the use of plant growth regulators (PGRs) – which is not permitted, but can happen – or day length treatments can have. The result of this could be that characteristics have to be assessed with caution or that the trial has to be extended to allow natural expression to be observed. ARE THERE MOLECULAR SOLUTIONS? To help manage reference collections and ensure effective com- parisons, molecular techniques could be used as a tool to screen varieties before the growing trial has started. Practical exam- ples of identifying the most similar varieties using molecular techniques are being developed for some crops within the DUS testing system ensuring that existing standards that dictate whether a variety is considered ‘clearly distinct’ are not eroded. In these cases, it is expected that a candidate variety is grown alongside the most similar varieties to confirm that there is a morphological difference. This would allow a reduction in the number of varieties in the growing trial, which saves time and resources, therefore making the test more cost effective. Using DNA databases to select the most similar varieties DUS TESTING AND MOLECULAR TECHNIQUES A view from the UK plant breeder’s rights office. BY: MARGARET WALLACE