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United States Department of Agriculture

Agricultural Research Service

Research Project: Genetic Enhancement of Allium, Cucumis, and Daucus Germplasm

Location: Vegetable Crops Research Unit

Title: Variation for epicuticular waxes on onion foliage and impacts on numbers of onion thrips

Authors
item Damon, Steve -
item Groves, Russell -
item Havey, Michael

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 21, 2014
Publication Date: July 1, 2014
Citation: Damon, S., Groves, R., Havey, M.J. 2014. Variation for epicuticular waxes on onion foliage and impacts on numbers of onion thrips. Journal of the American Society for Horticultural Science. 139(4):495-501.

Interpretive Summary: Natural variation exists in onion for amounts of waxes on leaves, and plants with lower amounts of these waxes suffer less damage from the insect thrips, which is the most important insect pest of onion. Wild-type onion possesses copious amounts of epicuticular waxes and is often referred to as waxy. The glossy phenotype has significantly less wax relative to waxy types. Phenotypes intermediate between waxy and glossy also exist in onion, which we will refer to as semi-glossy. Epicuticular waxes on the leaves of glossy, semi-glossy, and waxy onions were evaluated for appearance using Scanning Electron Microscopy and amounts and types were analyzed using Gas Chromatography/Mass Spectrometry. Wax crystals were clearly visible on the surface of waxy foliage, with decreasing amounts on semi-glossy and none on glossy leaves. Hentriacontanone-16 was the most prevalent wax on leaves of waxy onion and was significantly reduced on glossy and semi-glossy accessions. Numbers of thrips adults and larvae were significantly reduced on glossy and/or semi-glossy accessions relative to waxy in field and cage experiments. These results indicate that the semi-glossy phenotype may possess adequate amounts of epicuticular waxes to protect leaves from environmental and spray damage while still conferring resistance to thrips. This information will be useful to breeders and productionists as an integral part of management strategies for this important onion pest.

Technical Abstract: Natural variation exists in onion for amounts of epicuticular waxes on foliage, and plants with lower amounts of these waxes suffer less damage from the insect pest Thrips tabaci (thrips). Wild-type onion possesses copious amounts of epicuticular waxes and is often referred to as “waxy”. The recessively inherited “glossy” phenotype has significantly less wax relative to waxy types. Phenotypes intermediate between waxy and glossy also exist in onion, which we will refer to as “semi-glossy”. Epicuticular waxes on the leaves of glossy, semi-glossy, and waxy onions were evaluated for appearance using Scanning Electron Microscopy (SEM) and amounts and types were analyzed using Gas Chromatography/Mass Spectrometry (GCMS). Wax crystals were clearly visible on the surface of waxy foliage, with decreasing amounts on semi-glossy and none on glossy leaves. The ketone hentriacontanone-16 was the most prevalent wax on leaves of waxy onion and was significantly reduced (p<0.01) on glossy and semi-glossy accessions. Numbers of thrips adults and larvae were significantly reduced (p<0.05) on glossy and/or semi-glossy accessions relative to waxy in field and cage experiments. These results indicate that the semi-glossy phenotype may possess adequate amounts of epicuticular waxes to protect leaves from environmental and spray damage while still conferring resistance to thrips, and should be useful for integrated management of this important onion pest.

Last Modified: 10/24/2014
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