Walnut Scion & Rootstock Improvement
Walnut Scion & Rootstock Improvement
Walnut Scion & Rootstock Improvement
University of California
Walnut Scion & Rootstock Improvement

Genomics & Mapping Team

Inputs:

Open pollinated and interspecific hybrid seedlings and clonal plants; data on disease resistance of germplasm; English walnut single nucleotide polymorphism (SNP) map and genomic information.

Activities:

Create association and biparental maps of disease resistance based on SNP segregation and disease resistance in OP and hybrid populations.

Outputs:

Comparative genetic maps of wild spp.; linkage of resistance loci and SNP markers; genetic information for use in breeding; genetic publications and databases.

Short Term Outcomes:

Mapped  markers linked to genes conferring disease resistance; comparative linkage maps for examination of other traits in walnut germplasm.

Long Term Outcomes:

Marker assisted selection used in rootstock breeding; gene pyramiding; combined resistance to several pathogens in single rootstocks.

Impact:

Genetic information will accelerate development of improved walnut rootstocks and improve breeding options.

Half-sub progenies of wild Juglans spp.

Preliminary analysis of heritance variance for A. tumefaciens and P. cinnamomi resistance revealed statistically significant levels of additive genetic variance. These data facilitated the selection of mother trees for use in making interspecific crosses to generate mapping populations.

These results suggested two things:

  1. The complex polygenic nature of disease resistance in walnut is likely governed by a network of quantitative trait loci (QTLs).
  2. We will make genetic gains in disease resistance breeding, i.e. there exist mother trees with superior breeding value for disease resistance.

Juglans sp.

Team Members

Project Leader:
Malli Aradhya

Malli Aradhya
Malli Aradhya
Abhaya Dandekar
Abhaya Dandekar
Jan Dvorak
Jan Dvorak
Ming-Cheng Luo
Ming-Cheng Luo
David Neale
David Neale

Mapping genetic loci

We will identify the genetic loci which mediate disease resistance. This will facilitate development of molecular markers associated with disease resistance which, in turn, will accelerate improvement of walnut rootstocks.

To achieve this goal, we are mapping resistance genes on genetic maps relative to molecular markers. Molecular markers linked to resistance genes will facilitate:

  1. Efficient selection of resistant progeny in interspecific hybrids between wild mother trees and English walnut without pathogen challenge.
  2. Combining resistance against multiple diseases in a single rootstock.
  3. Pyramiding different genes for resistance to the same disease in a single rootstock.
  4. Screening large rootstock populations for most desirable phenotypes.

New genomic technology, Nanomapping (left). SNP-based genetic map of the English walnut genome (right).
New genomic technology, Nanomapping (left). SNP-based genetic map of the English walnut genome (right).

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