|Heusden, Sjaak van|
Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/14/2005
Publication Date: 1/11/2006
Citation: Mccallum, J., Clarke, A., Sheffer, J., Sims, I., Heusden, S., Shigyo, M., Havey, M.J. 2006. Genetic mapping of a major gene affecting onion bulb fructan content. Journal of Theoretical and Applied Genetics. 112:958-967. Interpretive Summary: The dry matter content of onion bulbs consists primarily 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 in onion bulbs. Bulb carbohydrate composition was evaluated in crosses between high and low dry matter onions. Reducing sugar (fructose and glucose) and fructan content showed high negative correlations and segregations suggestive of a major gene. A polymorphic genetic marker on chromosome 8 was identified which was strongly associated with bulb fructan content. This locus, named Frc, may account for the major phenotypic differences in bulb carbohydrate content between storage and sweet onion varieties. This information is important for onion breeders for the development of sweeter onion populations for US and world markets.
Technical 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 F2:3 families from the ‘W202A’ × ‘Texas Grano 438’ mapping population evaluated in two environments. This marker was mapped to chromosome 8 in the interspecific population ‘Allium cepa × A. roylei’. Mapping in the ‘Colossal Grano PVP’ × ‘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’ × ‘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.