Multiplication and Evaluation of Tissue Culture Derived Walnut Plants

The purpose of this project was to use and improve current walnut tissue culture methodology to generate plants from somatic embryos and from mature Juglans regia cultivars. Ninty-eight somatic embryo derived plants are now in soil. Fiftyfour of these are derived from the same embryogenic line. Plants from the same line are phenotypically uniform with the exception of 15% which exhibit thickened leaves, and abnormal bud development. This variant does not appear to be associated with lack of chilling. Modifications in the procedure for obtaining plants from embryogenic lines has improved the rate of survival from embryo to potted plant from 5 to 13%. Modifications included omission of cold treatment, pretreatment of selected embryos with GA3 and addition of activated charcoal to basal medium used for germlnation. Ten mature cuItivars were initiated into culture. Chandler is now in the multiplication phase and Sunland and Vina are approaching that phase. Problems encountered in micropropagation of mature J. regia cultivars included inadequate explant sterilization, latent contamination and 'slow decline'. Slow decline is characterized by gradual leaf chlorosis, leaf abscission and eventual death. Inadequate sterilization was overcome by rinsing explants for 2 hrs in running tap water prior to sterilization and by using individual rather than batch sterilization procedures. Antibiotic supplements to the medium were not effective in elminating contamination. Slow decline, which may be a result of lack of juvenility, was unaffected by several media adjustments. It was somewhat overcome by rapid transfer.