Abstract
Walnut shell suture strength directly impacts the ability to maintain shell integrity during harvest and processing, susceptibility to insect damage and other contamination, and the proportion of kernel halves recovered during cracking. Suture strength is therefore an important breeding objective. Here, two methods of phenotyping this trait were investigated: 1) traditional, qualitative and rather subjective scoring on an interval scale by human observers, and; 2) quantitative and continuous measurements captured by a texturometer. The aim of this work was to increase the accuracy of suture strength phenotyping and to then apply two mapping approaches, quantitative trait loci (QTL) mapping and genome wide association (GWAS) models, in order to dissect the genetic basis of the walnut suture trait. Using data collected on trees within the UC Davis Walnut Improvement Program (n = 464), the genetic correlation between the texturometer method and qualitatively scored method was high (0.826). Narrow sense heritability calculated using quantitative measurements was 0.82. A major QTL for suture strength was detected on LG05, explaining 34% of the phenotypic variation; additionally, two minor QTLs were identified on LG01 and LG11. All three QTLs were confirmed with GWAS on corresponding chromosomes. The findings reported in this study are relevant for application towards a molecular breeding program in walnut.
Highlights
English walnuts grown in the United States are sold in-shell, primarily for export at 234,000 tons per year, and shelled for domestic market at 452,000 tons per year totaling 686,000 tons [1]
For the 24 families that contained more than 10 individuals, family 11–011 (95-026-16 × 03-001-3382) had the highest Least Square Mean (LSM) score (38.697 ± 0.886; n = 11), while family 11–029 (03-001-665 × 01-007-2) had the lowest LSM score (24.28 ± 0.886; n = 12)
We successfully demonstrated that the use of a texturometer, for measuring walnut shell suture strength, is more sensitive to capturing variation and can increase the detection of additive genetic component for this trait
Summary
English walnuts grown in the United States are sold in-shell, primarily for export at 234,000 tons per year, and shelled for domestic market at 452,000 tons per year totaling 686,000 tons [1]. The term in-shell refers to uncracked nuts containing the kernels within intact shells. Shelled walnuts undergo cracking and processing, during which the shell is cleaned and removed, and kernels are sorted for size, color and quality. The value of intact kernel halves is substantially greater than smaller kernel pieces.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
