Affiliation: | Department of Animal and Plant Sciences, The University of Sheffield, Sheffield S10 2TN, UK; Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK; Department of Chemistry, The University of Sheffield, Sheffield S10 2TN, UK; Author for correspondence (tel +44 1789 472063;fax +44 1789 470552;e-mail ). |