Field performance was assessed in 13 transgenic potato (Solanum tuberosum L.) lines from three cultivars expressing a selectable marker gene conferring kanamycin resistance. All lines developed unexpected changes in the phenotypic appearance of shoots, and/or poor tuber yield generally involving a reduced number of small tubers. Each independently selected transgenic line showed distinctly different changes in phenotypic appearance or yield performance. The observed changes were very uniform within each clonally propagated transgenic line, and were consistent in appearance over two seasons in the field. These changes were attributed to either epigenetic or genetic events occurring during the tissue culture phase of transformation. Efficient systems for the rapid selection and regeneration of transformed plant cells are therefore required to minimise the frequency of tissue culture induced variation in plant performance. H94026

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The importance of in vitro storage root development for the growth and survival of micropropagated asparagus (Asparagus cfficinalis L.) plants under greenhouse conditions was assessed in four genotypes ('CRD047', 'CRDlOO', 'CRDlOl', and 'CRD222'). Plants with greater development of in vitro storage roots exhibited higher survival rates and took less time for the initiation of new shoot growth during acclimatisation in a humidity tent immediately following transfer out of culture. They also had higher survival rates and greater shoot growth on an open greenhouse bench 9 weeks following transfer from in vitro culture. An ideal micropropagated asparagus plant for greenhouse establishment consists of an in vitro minicrown supporting 4-6 shoots and 3-4 storage roots (3-4 em long). Such plants typically develop on a high-sucrose rooting medium.