Submitted to: Walnut Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/28/2011
Publication Date: 1/1/2012
Citation: Clonal propagation of walnut rootstock genotypes for genetic improvement 2011. Walnut Research Conference. 2011:103-128. Interpretive Summary:
Technical Abstract: This year we produced more than 9700 liner-sized plantlets of 83 genotypes for use in greenhouse and field pest and disease resistance screening, growth in nurseries, and development of orchard trials. These included 6200 plants of 33 new Juglans microcarpa x ‘Serr’ paradox genotypes and 230 plants of eleven additional J. cathayensis x ‘Serr’ or ‘Serr’ x J. cathayensis hybrid clones. Microshoots rooted and acclimated in the greenhouse were grown to appropriate size and condition for pathogen testing and provided to cooperators for greenhouse and field pests and disease trials. Our production included over 900 plantlets of 16 transgenic lines exhibiting resistance to crown gall for use in greenhouse, field, and orchard trials. Six lines have been chosen for further testing in nursery and orchard trials and one was selected as the leading candidate for pursuit of regulatory approval. The first field trial of transgenic crown gall resistant lines was established in 2008 at UC Davis and grafted to Chandler. Trees in this trial were used this year to supply bark and nut material for studies of trans-graft union movement of macromolecules. In greenhouse stab tests little variation was seen among clonal plantlets of 16 J. microcarpa paradox genotypes but seedlings of wingnut as accession DPTE 1.09 showed considerable differences with six of ten tested seedlings, stab tested for times each, producing no galls. Hardwood cuttings were used to produce clonal replicates of several seedling selections exhibiting potential crown gall resistance, methods for more rapid greenhouse germination of black walnut seed for paradox seedling production were examined, and we are attempting to develop methods for budding or grafting small container-grown plants. Field trials of clonal rootstocks continue to be established state-wide by farm advisors and we continue to supply plant material, assistance, and technical support to commercial laboratories and nurseries producing and selling improved clonal rootstocks.