title: Genetic mapping of a major gene affecting onion bulb fructan content.
abstract: The non-structural dry matter content of onion bulbs consists principally of fructose, glucose, sucrose and fructans. The objective of this study was to understand the genetic basis for the wide variation observed in the relative amounts of these carbohydrates. Bulb carbohydrate composition was evaluated in progeny from crosses between high dry matter storage onion varieties and sweet, low dry matter varieties. When samples were analysed on a dry weight basis, reducing sugar and fructan content exhibited high negative correlations and bimodal segregation suggestive of the action of a major gene. A polymorphic SSR marker, ACM235, was identified which exhibited strong disequilibrium with bulb fructan content in F(2:3) families from the 'W202A' x 'Texas Grano 438' mapping population evaluated in two environments. This marker was mapped to chromosome 8 in the interspecific population 'Allium cepa x A. roylei'. Mapping in the 'Colossal Grano PVP' x 'Early Longkeeper P12' F2 population showed that a dominant major gene conditioning high-fructan content lay in the same genomic region. QTL analysis of total bulb fructan content in the intraspecific mapping population 'BYG15-23' x 'AC43' using a complete molecular marker map revealed only one significant QTL in the same chromosomal region. This locus, provisionally named Frc, may account for the major phenotypic differences in bulb carbohydrate content between storage and sweet onion varieties.
authors.affiliation: New Zealand Institute for Crop and Food Research Limited, Private Bag 4704, Christchurch, New Zealand. mccallumj@crop.cri.nz
authors.forename: John
authors.initials: J
authors.lastname: McCallum
authors.forename: Andrew
authors.initials: A
authors.lastname: Clarke
authors.forename: Meeghan
authors.initials: M
authors.lastname: Pither-Joyce
authors.forename: Martin
authors.initials: M
authors.lastname: Shaw
authors.forename: Ruth
authors.initials: R
authors.lastname: Butler
authors.forename: Don
authors.initials: D
authors.lastname: Brash
authors.forename: John
authors.initials: J
authors.lastname: Scheffer
authors.forename: Ian
authors.initials: I
authors.lastname: Sims
authors.forename: Sjaak
authors.initials: S
authors.lastname: van Heusden
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Shigyo
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Havey
mesh_terms: D001947:Breeding; D002874:Chromosome Mapping; D005630:Fructans / Q000032:analysis*; D008040:Genetic Linkage; D005819:Genetic Markers; D014644:Genetic Variation; D019697:Onions / Q000033:anatomy & histology / Q000737:chemistry / Q000235:genetics; D010641:Phenotype; D011110:Polymorphism, Genetic; D040641:Quantitative Trait Loci; D013223:Statistics as Topic
chemical_list: D005630:Fructans; D005819:Genetic Markers