Quantitative Trait Loci Controlling Amounts and Types of Epicuticular Waxes in Onion

Natural variation exists in onion (Allium cepa L.) for amounts and types of epicuticular waxes on leaves. Wild-type waxy onion possesses copious amounts of these waxes, whereas the foliage of semiglossy and glossy phenotypes accumulates significantly less wax. Reduced amounts of epicuticular waxes have been associated with resistance to onion thrips (Thrips tabaci Lindeman), an important insect pest of onion. A segregating family from the cross of waxy and semiglossy onions was used to map single nucleotide polymorphisms (SNPs) and identify chromosome regions affecting amounts and types of epicuticular waxes as measured by gas chromatography–mass spectrometry. The amount of the primary epicuticular wax on onion leaves, hentriacontanone-16, was controlled by one region on chromosome 5. One region on chromosome 2 affected concentrations of several primary fatty alcohols. Results indicate that the region on chromosome 2 may be associated with the acyl reduction pathway, and the region on chromosome 5 may affect the decarbonylation pathway of epicuticular wax biosynthesis. Because lower amounts of epicuticular waxes are recessively inherited, SNPs tagging regions on chromosomes 2 and 5 will be useful for marker-assisted breeding to vary amounts and types of epicuticular waxes on onion foliage with the goal to develop cultivars resistant to onion thrips.