Plant Science

Uniformity of plant varieties

The introduction of new varieties of plants is regulated by a process known as National Listing, and for many crop types only varieties on the National List may be marketed. As well as seeking inclusion in the National Lists, developers of new varieties may also apply for Plant Breeders’ Rights which if successful will secure intellectual property protection for these varieties. One requirement to qualify for these is that the new variety is sufficiently uniform in its relevant characteristics.

Where the characteristics are quantitative in nature, e.g. height, then the uniformity may be assessed by comparing variability with similar varieties. A widely-used statistical method for carrying out this comparison is known as the Combined-Over-Years Uniformity method (COYU) which uses a moving-average adjustment method to ensure that comparisons allow for relationships between variability and mean values. However it has been shown that this adjustment method leads to a bias, making COYU too strict.

In collaboration with the University of Aarhus, and supported by the Community Plant Variety Office, Defra and SASA, we have investigated approaches for improving the COYU method. We found that a cubic smoothing spline with low degrees of freedom fitted the relationships between variability and level of expression seen in practice. Using this alternative approach, we have proposed an alternative to the existing COYU method so that the bias is now minimal.

The process of gaining acceptance of the improved method by UPOV, the governing body, will take some time. To assist this, and to expedite uptake of the improved method following acceptance, we are now working with the Agri-Food and Biosciences Institute to produce software for worldwide circulation.

two carrots on a grid We have developed a new approach to allowing for relationships between variation and mean values in variety trials conducted to assess the uniformity of varieties.

Further details from: Adrian Roberts and Graham Horgan

Article date 2013

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