Date of Award

12-2016

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Agronomy

First Advisor

Torbert R. Rocheford

Committee Chair

Torbert R. Rocheford

Committee Member 1

Mario G. Ferruzzi

Committee Member 2

Jianxi Ma

Committee Member 3

William M. Muir

Abstract

Pro-Vitamin A (proVA) carotenoids, which are converted into retinol (Vitamin A) in the human body, have been the subject of human nutrition studies and are a target for biofortification of staple crops. Historically, β-carotene has been the principal target for enhancing levels of proVA, yet there is recent interest in enhancing the proVA carotenoid β-cryptoxanthin. Studies have shown that β-cryptoxanthin has excellent bioavailability, and its use in maize may be nearly as effective as β-carotene in providing retinol. The primary aim of this study was to gain a better understanding of the genetic control of levels of β-cryptoxanthin, conversion of β-carotene into β-cryptoxanthin, conversion of β-cryptoxanthin into zeaxanthin, and flux into the β-branch of the carotenoid pathway. We studied a biparental population derived from inbreds with relatively high levels of β-cryptoxanthin and different ratios of β-cryptoxanthin to β-carotene. Three field replications of this F2:3 population were grown and the grain analyzed by liquid chromatography (LC) with diode array detection. Data from a previous study using two color assessment methods, visual score and chromameter readings, were included to associate and compare LC and color results. Composite interval mapping (CIM) identified 90 quantitative trait loci (QTL). Notably, we detected a QTL for Ratio 3 (β-carotene / [β-cryptoxanthin + zeaxanthin]) and Ratio 5 ([β-carotene + β-cryptoxanthin] / zeaxanthin) on chromosome 2 that contains candidate gene hydroxylase 4 (hyd4), which has not been previously associated with QTL for carotenoids in maize grain. A common finding for LC and chromameter data included a QTL on chromosome 5 for β-carotene, zeaxanthin, β-carotene + β-cryptoxanthin, β-branch proVA, cisβC, Total carotenoids, Ratio 1 (β-carotene / β-cryptoxanthin + zeaxanthin), h, h99 and b*. This region contains candidate gene lycopene β cyclase (lcyβ). This new information could potentially be used in biofortification breeding programs to increase the content of proVA and the total carotenoids in maize.

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