Identities of and Phenotypic Variation for Epicuticular Waxes among Leaves and Plants from Inbred Onion Populations

Abstract

The amounts and types of epicuticular waxes on onion (Allium cepa) leaves affect feeding damage by onion thrips (Thrips tabaci). This study used gas chromatography mass spectrometry (GCMS) to establish the identities of waxes and measure over time wax amounts on leaves of inbred onion plants with glossy, semiglossy, and waxy foliage. Nine waxes were detected on leaves of all inbreds, and higher coefficients of variation (cv) were observed for less abundant waxes on foliage of doubled haploid onions. Older leaves had higher amounts of waxes compared with younger leaves on the same plant. Except for one minor wax, amounts of individual waxes on leaves were not significantly different for plants of different ages. There was a significant inbred by sampling date interaction due to lower amounts of waxes on the leaves of older plants from the semiglossy inbred. These results indicate that there is little advantage to multiple samplings of leaves over time from the same plant and resources may be better used to evaluate more plants. The relatively large cvs for amounts of specific waxes may reduce response to selection for unique epicuticular wax profiles to develop onion populations that suffer less feeding damage by onion thrips.

Phenotypic Variation for Epicuticular Waxes Across Plant Introductions of Onion

“…Our results indicate that amounts of waxes on onion foliage should be measured under protected conditions to better reveal phenotypic variation. We previously reported that multiple sampling of leaves on the same plant over time and environments may not be necessary (Khosa et al, 2020), and resources may be better used to sample greater numbers of plants. Reducing the amount of H16 while maximizing amounts of fatty alcohols and/or alkanes may produce onion populations with semi-glossy foliage that accumulate enough total epicuticular wax to perform well in field production.…”

“…Data analysis. Post-run GCMS analyses (Shimadzu) were used to determine peak areas and identities of waxes as described by Khosa et al (2020). Peak areas were adjusted by dividing the peak areas for docosane and therefore represent peak areas per gram leaf fresh weight.…”

“…The composition of lipids that form epicuticular waxes differs among plant species (Baker, 1982;Eigenbrode and Espelie, 1995). Khosa et al (2020) reported that the primary waxes on onion (Allium cepa) foliage are the fatty alcohols heptadecanol-1 (Hept1), hexacosanol-1 (Hex1), octacosanol-1 (Oct1), and triacontanol-1 (Tri1); alkanes heptacosane (Hept), nonacosane (Non), and hentriacontane (Hent); ether 1-ethenyloxyoctadecane (Octd); and ketone hentriacontanone-16 (H16).…”

Genetic Analysis of the Unique Epicuticular Wax Profile of ‘Odourless Greenleaf’ Onion

“…To prepare for gas chromatographymass spectrometry (GCMS), dried wax extracts were dissolved in 250 mL chloroform, 300 mL acetronitrile (HPLC grade; Thermo Fisher Scientific), and 105 mL N,O bis(trimethylsilyl) trifluoro-acetamide (HPLC/GC grade; Sigma-Aldrich) and incubated for 30 min at 80°C. Identification and quantification of waxes involved the GCMS conditions described by Damon et al (2014) and Khosa et al (2020).…”