Groot, S.P.C.; Jalink, H.; Hospers-Brands, M.; Köhl, J.; Veerman, A.; Wenneker, M.; van der Wolf, J.M. and van den Bulk, R.W (2006) Improvement of the quality of propagation material for organic farming system. Joint Organic Congress, Odense, Denmark, May 30-31, 2006.