Author: Eduardo Dominguez-Munaiz

Publisher:

Published: 2018

Total Pages: 0

ISBN-13:

Epicuticular waxes are important for plant defense against pathogens and insects. In onion (Allium cepa L.), the insect onion thrips (Thrips tabaci Lindenman) is the most important pest and can cause 50% yield loss. T. tabaci is also the principal vector of Iris yellow spot virus (IYSV) which can cause over 40% yield loss. Lower amounts of epicuticular waxes on onion leaves has been associated with fewer thrips, less feeding damage, and lower incidence of IYSV. The goals of this project were: 1) document wax profiles across phenotypically different onion accessions and its relationship with thrips damage; 2) develop a genetic model for wax accumulation to better understand the glossy phenotype; and 3) develop of a model to estimate concentrations of the chemical wax constituents on living leaves using chemometrics. Natural variation for amounts and types of waxes was revealed among accessions. Hentriacontanone-16 (H16) and Octacosanol-1, the most prevalent waxes in wild-type onions, were significantly lower in semi glossy (SG) types. Glossy phenotypes possessed the lowest amount of H16 but can possess larger amounts of other waxes. The proportion of H16 to total wax varied from 72% in waxy phenotypes to 43% in the glossy inbred. There were semi glossy accessions with larger total wax amounts than waxy phenotypes, due to lower quantities of H16. Broad sense heritabilities were high for H16, Octacosanol-1 and Triacontanol-1 at 0.93, 0.72, and 0.87, respectively. Pearson correlations across environments were high averaging 0.82 for H16 and lower for the fatty alcohols, probably due to relatively lower amounts of these waxes. Glossy and semi-glossy phenotypes supported fewer thrips and lower damage relative to waxy phenotypes. Foliage glossiness in two segregating families (B9885 x B5351 and B9885 x B8667) revealed a QTL on chromosome 8. Visual glossiness in the cross of glossy B9885 by waxy B8667 was associated with a region on chromosome 8, and this same region had the largest effect on H16 accumulation in the glossy (B885) by semi glossy (B5351) cross. It can be concluded that a glossy locus is located on chromosome 8. In the cross B9885 x B5351, three QTL accounted for 41 % of the phenotypic variation with LOD score 22.4. The allele substitution effect on chromosome 8 from the semi glossy parent B5351 increased H16 amounts. However, the region on chromosome 5 from the semi glossy parent reduced the amounts of H16. For H16, epistasis was detected between regions on chromosomes 1 and 8, and higher amounts of H16 were conditioned by the homozygous genotype on chromosome 1 from the semi glossy parent and homozygous recessive on chromosome 1 from the glossy parent. Fatty alcohol amounts revealed a single QTL on chromosome 1 at 0.0 cM explaining a large proportion of the phenotypic variation in the greenhouse and under field. Spectral measurements on fresh leaves revealed major absorption features for wax constituents. Wavelengths in the visible, near infrared and short-wave infrared (SWIR) were associated with H16, Octacosanol-1 and Triacontanol-1. The fingerprint of each wax constituent was also due to an additive effect of multiple spectral features.