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11140010 PhD Mapping Starch and Glycaemic Index (GI)

Publication Date: 
30 July 2014
Author/Contact :
Author/Contact: 
Mark Taylor

Contractor :
Contractor: 
James Hutton Institute (JHI)

Full Research Project Title: Application of association mapping and genomic sequencing to starch and glycaemic index in potato
Duration: October 2013 - September 2016

Background

Potatoes have a typically of high glycaemic index (GI), although published GI values are highly variable depending on potato variety and processing/ cooking methods, GI is becoming a major determinant of consumer preference and some new cultivars are being marketed primarily on the basis of their low GI.  There is a need to identify the inherent factors that influence this trait, and to find potatoes of reduced GI to address consumer concerns. This could potentially help to avoid loss of market share to other starch sources competing with potatoes.

Collaboration

James Hutton Institute (JHI), Rowett Institute of Nutrition and Health, Greenvale AP

Aims and objectives

Aim:  To determine the degree of variation that exists in GI-related traits across a diverse range of potato germplasm. There are a number of factors that may affect the GI of potatoes, including starch structure, ratio of amylose and amylopectin, the level of processing, cooking technique, and the presence of other nutrients such as fat, protein, and dietary fibre.

Objectives:

a) To phenotype varieties over 2 years for factors contributing to glycaemic index: including dry matter, sugars and levels of resistant starch.
b) To understand the associations of phenotype and genotype data which will provide new insights into factors that influence GI in potatoes.
c) To identify key genes as well as development of diagnostic markers for starch qualities and ultimately new varieties with improved GI characteristics.
 
Approach

This PhD studentship project will use an association genetics approach to identify genes that are important in traits related to glycaemic index (GI). Varieties will be phenotyped over 2 years in replicated trials for factors including dry matter, sugars and levels of resistant starch. The associations of phenotype and genotype data will provide new insights into factors that influence GI in potatoes. Genome- Wide Association Studies (GWAS) can be used to dissect trait variation across much broader germplasm populations than conventional genetic mapping of biparental crosses. In comparison to traditional linkage analysis, it offers significant advantages such as increased mapping resolution, reduced research time, and greater allele number.

Genotyping by sequencing data is already available from an elite association mapping panel of ~300 potato varieties. In order to use association genetics, varieties will be analysed over two years for traits contributing to GI.

Key Findings

The starch digestibility characteristics of samples from the 300 genotypes used in the study were determined. Trials were conducted over two growing seasons, using a replicated block design. Consistent variation in starch properties between the genotypes was observed in the year 1 trial. The starch digestibility characteristics were used in an association mapping approach using the SolCAP SNP marker data available for the association panel (ca. 8300 SNPs) and 44700 SNP markers available from a genotype-by-sequencing approach. Significant associations with starch digestibility were detected using the first trial. For the second trial the data were not well correlated between the two blocks used in the trial or with the first trial. A reproducible and reliable starch digestibility assay has been developed. The assay requires 100 mg of starch and measures glucose release over 60 minutes. Compared with previous methods, this is a high throughput assay that can be used to assess many samples simultaneously.

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