Association genetics of carbon isotope discrimination and leaf morphology in a breeding population of Juglans regia L.

Randi A. Famula,James H. Richards,David B. Neale,Thomas R. Famula

doi:10.1007/s11295-018-1307-4

Randi A. Famula, James H. Richards + Show 2 more

Open Access

https://doi.org/10.1007/s11295-018-1307-4

Copy DOI

Abstract

English walnut (Juglans regia L.) is an economically important crop with > 99% of US walnuts produced in California. Changes in climate and recent drought cycles have raised concerns regarding the future of nut production and responsible water use in California agriculture. Our study used an association genetics approach to characterize ecophysiological traits such as water use efficiency as estimated by carbon isotope discrimination (Δ13C), and photosynthetic capacity through foliar nitrogen composition, in important individuals of the Walnut Improvement Program, located at the University of California, Davis. Stable isotope and leaf measurements of 241 mature trees, representing 60 scion genotypes in established orchards were sampled in 2015 and 2016, followed by genotyping with the Walnut Axiom 700 k SNP Array. A mean Δ13C of 21.7‰ (σ: 0.9‰) was calculated for all individuals, as well as a mean nitrogen/leaf area (N/area) of 3.0 gN/m2 (σ: 0.5 gN/m2). A Bayesian analysis utilizing genomic relationships revealed rankings of the most water use efficient accessions as Solano (95-011-16), 67-013 (unreleased cross), and Tulare (67-011). 126,554 SNPs were used in a two-step association genetics approach identifying four loci associated with Δ13C after correction for multiple testing. Investigation of identified loci revealed an annotation on the J. regia genome of protein FAR1-related sequence 5-like, related to abiotic stress response. For uncharacterized markers, homologs were identified in Arabidopsis for two loci, similarly related to drought stress.

Highlights

The Persian, or English, walnut (Juglans regia L.) is the most economically important species of the Juglandaceae family, and is the only species of the Juglans genus widely cultivated for nut production (McGranahan and Leslie, 2012)
Established in 1948, the Walnut Improvement Program (WIP) has released all major cultivars grown in California, including the variety Chandler, which accounts for 53% of all bearing trees in California and 75% of all nursery sales (Ramos 1998; USDA-NASS 2016, 2017)
Prior to 2005, clonal rootstocks were not utilized in the WIP germplasm blocks; genetic scion-rootstock combinations were not replicated in this experiment

Summary

Introduction

The Persian, or English, walnut (Juglans regia L.) is the most economically important species of the Juglandaceae family, and is the only species of the Juglans genus widely cultivated for nut production (McGranahan and Leslie, 2012). In North America, walnuts are almost entirely grown in California, Communicated by S. With a farm-gate value of $1.9 billion in 2014, and acreage has increased rapidly over the last decade to 127,500 bearing hectares (USDA NASS 2016). Walnut contributes substantially to California’s economy, with the only commodity walnut breeding program in North America located at the University of California, Davis. Established in 1948, the Walnut Improvement Program (WIP) has released all major cultivars grown in California, including the variety Chandler, which accounts for 53% of all bearing trees in California and 75% of all nursery sales (Ramos 1998; USDA-NASS 2016, 2017). While recent breeding in California has focused on production and yield-based traits, such as lateral bearing, harvest date, and kernel color (Martínez-García et al, 2017). Few objectives in the program have addressed the environmental challenges facing California, such as water use

Objectives

Methods

Results

Discussion

Conclusion