Project Number: 5306-22000-015-22
Project Type: General Cooperative Agreement

Start Date: Sep 01, 2012
End Date: Aug 31, 2014

Objective:
1)Assemble germplasm and develop genetic and association mapping populations for mapping genetic loci mediating disease resistance. (Leslie) 2)Conduct studies to elucidate host selection behavior of walnut twig beetle the vector of Geosmithia morbida the causal agent of Thousand cankers disease of walnut. (Bostock) 3)Identify and develop Single-nucleotide polymorphisms (SNP) markers and the associated SNP genotyping platform (Dvorak, Dandekar) 4)Quantify the economic impact of disease-resistant rootstocks on the US walnut industry(Klonsky, Lampinen)

Approach:
1)Will work with the USDA-ARS, National Clonal Germplasm Repository for selection of mother tree panels and assembly of OP (open-pollinated) seedlings, assembly of interspecific hybrid seedlings, and propagation techniques. Selected germplasm will include Juglans spp. currently used in walnut rootstocks as well as novel species that offer promising levels of disease resistance. 2)Will work with the USDA-ARS, National Clonal Germplasm Repository to evaluate mature trees by inoculating healthy, intact branches with local isolates of G. morbida. After 6 weeks, inoculated branches will be excised and evaluated for canker development. Will work with USDA Forest Service in Davis CA on Walnut Twig beetle. Evaluated WTB to understand the extent to which Thousand cankers disease epidemic is being driven by host preferences. 3)Walnut trees derived from crosses of resistant MTs with English walnut and OP trees of wild walnut species for association mapping will be genotyped using GBS. 4)Examine the economics of clonal rootstock use-the costs and income associated with orchard establishment for each rootstock. The price to growers of the clonal trees produced in pots, clonal trees field grown and conventional trees will be collected from the major nurseries supplying trees to the walnut industry. Harvest costs will be estimated based on the yields extrapolated to a 40 acre block. The effect of rootstocks on yield will be analyzed by monitoring canopy growth dynamics as determined by measuring interception of photosynthetically active radiation.