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

Abstract

<jats:p>Natural variation exists in onion (<jats:italic>Allium cepa</jats:italic> 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 (<jats:italic>Thrips tabaci</jats:italic> 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.</jats:p>

Enhancing onion breeding using molecular tools

“…). Glossy and semi‐glossy foliage has been shown to be non‐preference to thrips feeding damage in onion (Damon and Havey ). Genetic studies indicate low heritability for thrips resistance, and it would be desirable to use family based selection to increase genetic gain (Hamilton et al.…”

“…In recent years, it has been observed that onion has natural variation for the amount and types of epicuticular waxes (Bag et al. , Damon and Havey ). Onion accessions with glossy or semi‐glossy foliage have lower wax content, which associated with non‐preference to onion thrips.…”

“…SNP markers tagged with these regions are being identified for marker‐assisted breeding to alter the amounts and types of epicuticular waxes to develop cultivars resistant against onion thrips (Bag et al. , Damon and Havey ).…”

“…Germplasm from different countries has been evaluated and a few tolerant sources identified, which can be utilized in breeding programmes (Diaz-Montano et al 2011, Bag et al 2014. Glossy and semi-glossy foliage has been shown to be non-preference to thrips feeding damage in onion (Damon and Havey 2014). Genetic studies indicate low heritability for thrips resistance, and it would be desirable to use family based selection to increase genetic gain (Hamilton et al 1999).…”

Tyramide-FISH mapping of single genes for development of an integrated recombination and cytogenetic map of chromosome 5 ofAllium cepa

“…In this study we used onion EST clones and sequences available from the NCBI database to develop DNA probes for in situ hybridization to onion chromosome 5. We focused on chromosome 5 because it carries major quantitative trait loci (QTL) of interest to breeders that control bulb dry-matter content, pungency and storability, leaf waxiness, and resistance to abiotic factors (McCallum et al 2007;Masamura et al 2012;Damon and Havey 2014). We describe a new approach of DNA probe development based on producing exon-intron containing genomic fragments using PCR with primers designed on known exon sequences.…”