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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Research Project #436353

Research Project: Putting Phenotypic and Genotypic Tools to Work for Improving Walnut Rootstocks

Location: Crops Pathology and Genetics Research

Project Number: 2032-22000-016-55-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Jun 1, 2019
End Date: Jul 15, 2020

1. Traditional and in vitro propagation of a genetically diverse collection of Juglans species including creation and characterization of an enhanced mapping population from Juglans microcarpa x J. regia crosses. 2. Genotypic description of genetic loci which mediate disease resistance. 3. Genetic, physical, and functional mapping of disease resistance genes and deployment of molecular markers for rapid screening/identification of resistant genotypes. 4. Outreach and development of new, and existing, field trials examining performance of elite rootstock germplasm.

1. Continue to produce seedling and in vitro clonal propagants from our collections that will be made available for disease resistance screening. New disease resistant genotype will be identified, and propagated under in vitro conditions in order to confirm its phenotype under a variety of conditions, including in field trials. 2. This objective comprehensively investigates several subobjectives: (a) Refinement of preliminary QTL maps for the three pathogen systems, (b) pyramiding resistance to all three pathogens aided by marker assisted selection (MAS), (c) strategically select SNP markers in the QTL intervals for crowngall, phytophthora and nematode resistances to fine-map the traits, identify close-linked markers and towards cloning the gene(s), and (d) map drought tolerance in the breeding families already genotyped. 3. , we will isolated genomic DNA from the 58 progenies by using standard plant genomic DNA isolation methods. We will design and synthesize primers to amplify eight SNP markers that appear to be with the identified 2Mbp interval. We will use our re-sequencing reads to call additional heterozygous SNPs in 31.09. 4. Continue evaluation of our five ongoing orchard rootstock trials (one trial each in Glenn, Lake, Sutter, Solano, and Tulare counties). All five of the elite selections, as well as commercial standards of Paradox seedling and VX211 and RX1 clonal rootstocks were grafted to scions of J. regia ‘Chandler’. We will continue to assess tree growth (i.e., annual tree trunk circumference measurements, percent of photosynthetically active radiation intercepted by tree canopy), disease incidence, and rootstock suckering. Crown gall incidence will be visually assessed, and roots from trees that decline or die will be examined to determine whether they are infected with Phytophthora spp. or lesion nematode. Tree performance data from all orchard trials will be subjected to analyses of variance and regression analyses, as appropriate.