FIELD PERFORMANCE OF TRANSGENIC WALNUTS

Department of Pomology, University of California, Davis, CA 95616 USA

Walnuts, Juglans, are a long-lived perennial tree crop with a generation interval of 3-10 years. Field trials of transgenic walnuts were initiated in 1989 (marker genes only) and again in 1994 with a variety of clones containing different genes. Each year additional clones are field-planted. Selection of the background genotype is based on precocity or commercial importance. A diversity of backgrounds has proven to be desirable because of potentially deleterious changes that occur during in vitro manipulations. At present, in the field are walnut trees containing the following: rol ABC , cry 1A(c) (synthetically reconstructed from Bacillus thuringiensis), GNA (snowdrop lectin), Xa21 (from rice), LFY (from Arabidopsis), and SAR8.2 (systemic acquired resistance). These also contain different promoters (CaMV35S or Ubi3) and markers (kanamycin resistance and GUS). Phenotypically all the trees appear similar to the untransformed controls except those containing rol ABC which are denser and darker green. Rooting trials with cuttings from the rol ABC trees suggest that they have potential to be multiplied for clonal rootstock but they have been grafted just recently with scion cultivars. The other genes have been shown to be effective in in vitro tests but only preliminary tests have been carried out in the field.