Identification of markers for quality traits in red raspberry

There is an unsatisfied demand for UK soft fruit. Growers need to produce fruit of premium sensory quality and enhanced shelf life primarily for fresh consumption across a wide season.

Soft fruit production for fresh consumption has been revitalised by new cultivation strategies including new raspberry varieties grown under protected cultivation. Currently estimated at a retail value of £62 million, growers recorded market growth of 32% over the past year. Predictions are for increases of 100%-200%, given availability of high quality varieties that meet market requirements across the season. Premium quality fruit from cultivars across the summer season is not possible through limitations in sensory characters and shelf life parameters. UK grower needs are ability to produce raspberries of premium quality, specifically under cover, from early to late in the season. Currently only three to four weeks of high quality UK raspberries are available, demand over the rest of the ‘traditional fruit season’ is met through imported fruit.

Currently consumers can be disappointed by high cost, poor flavour, limited shelf-life, short availability and quality compromise that discourage repeat purchases. Growers expend capital and effort in establishing specialised raspberry cultivation and need to achieve profitability by sale of fruit perceived of premium quality and readily available for harvest from robust plants. Traits of fundamental interest across the season to supply chain stakeholders are considered to be: sweetness and flavour intensity, berry conformation (drupelet structure and cohesion), colouration and firmness across the season.

What are required are the application of non-controversial state-of-the-art molecular technologies of proven success in other crops (for example, tomato and peach) that can ensure new varieties have specific sensory characters and quality parameters. In the raspberry this is now possible through the SCRI genetic map enabling studies on the inheritance of important traits to be carried out and will allow knowledge and technology transfer from other major Rosaceous crops.

A genetic linkage map is a representation of a plant’s chromosomes with signposts placed along the chromosome in the form of molecular markers, to which phenotypic traits can be associated. Such maps can facilitate the development of diagnostic markers for polygenic traits and the identification of genes controlling complex phenotypes. The map provides a means for locating and hence manipulating quantitative traits in breeding programmes. This linking phenotype to genotype, will greatly contribute to our understanding of the genetic control of commercially important traits and therefore our ability to combine desirable traits in the same cultivar. The establishment of gene-phenotype relationships will allow gene-based selection in breeding and the functional assignment of genes for traits such as disease resistance and fruit quality.

SCRI in collaboration with food scientists at Strathclyde University have studied fruit quality from the SCRI raspberry mapping population over a number of years and sites, collecting information on the biochemical basis of  taste, aroma and appearance. The mapping population, a cross between the American cv. Latham (sweet, aromatic, late-cropping, small and firm berries, glossy and of mid- to dark red colour) with the Scottish cv. Glen Moy (slightly sweet, early, large conical fleshy, dull pale-mid red fruit of aromatic character) segregate for all key traits of interest.

An understanding of how biochemical, sensory and genetic data relate to each other in terms of quality parameters will be determined and definitions of quality redefined.

OTLs underlying quality parameters have been identified for traits such as anthocyanin content, colour, volatiles, sensory perceptions and sugar and acids on the raspberry genetic linkage map and in conjunction with other data from candidate gene map locations, BAC library screening and sequencing and comparative mapping with another Rosaceous species, markers or in-fact the genes themselves have been identified and favourable alleles are being sought in a range of germplasm.

Figure: QTL for anthocyanin production

This work is funded through HortLink HL0170 with a range of industry partners.

Partners HDC, M&S plc, KG Fruits, MRS, T.Thomson Ltd Blairgowrie, ReDeva.