Genetic analysis of the unique epicuticular-wax profile of ‘Odourless Greenleaf’ onion

Authors: Havey, Michael; HUNSAKER, DEREK - University Of Wisconsin; MUNAIZ, EDUARDO - Biological Mission Of Galicia Spain

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2020
Publication Date: 1/27/2021
Citation: Havey, M.J., Hunsaker, D.J., Munaiz, E.D. 2021. Genetic analysis of the unique epicuticular-wax profile of ‘Odourless Greenleaf’ onion. Journal of the American Society for Horticultural Science. 146(2):118-124. https://doi.org/10.21273/JASHS05024-20.
DOI: https://doi.org/10.21273/JASHS05024-20

Interpretive Summary: Amounts and types of waxes on the leaves of onion affect feeding damage by onion thrips, the most serious insect pest of onion. The onion cultivar Odourless Greenleaf (OGL) shows resistance to thrips feeding damage, and has a unique wax profile accumulating significantly higher amounts of the waxes octacosanol-1 (Oct1), hexacosanol-1 (Hex)], and heptacosane (Hept). Plants of OGL were crossed with the low wax (glossy) inbred B9885 and high wax (waxy) inbreds DH2107, DH06669, and B8667. Hybrid progenies from all crosses had waxy foliage indicating recessiveness of the OGL phenotype relative to the waxy parents and a different genetic basis relative to the recessive glossy (glwp) locus of B9885. Hybrid plants were self pollinated and F2 segregations from the OGL by waxy crosses fit the expected 3:1 ratio for a single recessive locus. For families from crosses of OGL by glossy B9885 segregations fit the 9:7 ratio for two recessive loci. Amounts and types of epicuticular waxes on F2 progenies from OGL crossed with waxy B8667 and glossy B9885 were determined using gas chromatography mass spectrometry (GCMS). Single nucleotide polymorphisms (SNPs) were genotyped using DNAs from the F2 families and genetic maps constructed. The visually glossy phenotype from OGL and its unique profile of epicuticular waxes were conditioned by a single recessive locus on chromosome 6 of onion, for which we propose the name named gl-ogl. This research will be useful to onion breeders towards the development of onion populations with unique wax profiles that suffer less feeding damage from onion thrips.

Technical Abstract: Amounts and types of epicuticular waxes on the foliage of onion (Allium cepa) affect feeding damage by onion thrips (Thrips tabaci), the most serious insect pest of onion. The onion cultivar Odourless Greenleaf (OGL) shows resistance to thrips feeding damage, and has a unique wax profile accumulating significantly higher amounts of two fatty alcohols [octacosanol-1 (Oct1) and hexacosanol-1 (Hex)] and one alkane [heptacosane (Hept)]. Plants of OGL were crossed with the low wax (glossy) inbred B9885 and high wax (waxy) inbreds DH2107, DH06669, and B8667. Hybrid progenies from all crosses had waxy foliage indicating recessiveness of the OGL phenotype relative to the waxy parents and a different genetic basis relative to the recessive glossy (glwp) locus of B9885. Hybrid plants were self pollinated and F2 segregations from the OGL by waxy crosses fit the expected 3:1 ratio for a single recessive locus. For families from crosses of OGL by glossy B9885 segregations fit the 9:7 ratio for two recessive loci. Amounts and types of epicuticular waxes on F2 progenies from OGL crossed with waxy B8667 and glossy B9885 were determined using gas chromatography mass spectrometry (GCMS). Single nucleotide polymorphisms (SNPs) were genotyped using DNAs from the F2 families and genetic maps constructed. The visually glossy phenotype from OGL and its unique profile of epicuticular waxes were conditioned by a single recessive locus on chromosome 6 of onion, for which we propose the name named glogl. Onion populations such as OGL with unique epicuticular-wax profiles will be important germplasm for the development of onion cultivars that suffer less feed damage from onion thrips.