# Co-Location of QTL for Vigor and Resistance to Three Diseases in Juglans microcarpa × J. regia Rootstocks

## TL;DR

A genetic region in walnut rootstocks is linked to disease resistance and tree growth, suggesting shared genetic mechanisms.

## Contribution

A QTL on chromosome 4D is shown to co-locate resistance to multiple diseases and vigor traits in walnut hybrids.

## Key findings

- A QTL on chromosome 4D is associated with resistance to Agrobacterium tumefaciens and Phytophthora spp.
- The same QTL is co-located with vigor traits like tree height and Pratylenchus vulnus counts.
- Genomic selection models predict traits most accurately for two-year tree height.

## Abstract

A QTL on chromosome 4D of the Juglans microcarpa × J. regia genome that co-located resistance against Agrobacterium tumefaciens, Phytophthora pini, and Phytophthora cinnamomi disease scores was investigated for additional traits. Phenotypic data for Pratylenchus vulnus counts and tree height were analyzed in this study for the same hybrids previously used to identify this QTL. Using the same GBS genotype data, the same co-located QTL for A. tumefaciens and Phytophthora spp. disease scores were reproduced and the QTL for P. vulnus counts and tree height were co-located with resistance to A. tumefaciens and Phytophthora spp. Moreover, we found GBS genotype data to harbor additional genetic variation unrelated to any of the traits analyzed. Marker-assisted and genomic selection models were created and assessed for their performance in selection. The ability to predict traits using SNP data was strongest with two-year tree height, followed by A. tumefaciens disease score, three-year tree height, Phytophthora spp. disease score, and P. vulnus counts. These results suggest a shared mechanism of action that links disease to tree height. Moreover, deploying these selection models would assist efforts in walnut improvement for rootstock genotypes.