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Research Project: Genetic Enhancement of Watermelon, Broccoli, and Leafy Brassicas for Economically Important Traits

Location: Vegetable Research

Title: Genotyping-by-sequencing of waxy and glossy near-isogenic broccoli lines

item Branham, Sandra
item Farnham, Mark

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2017
Publication Date: 3/11/2017
Citation: Branham, S., Farnham, M.W. 2017. Genotyping-by-sequencing of waxy and glossy near-isogenic broccoli lines. Euphytica. 213:84-89.

Interpretive Summary: The surfaces of normal broccoli plants are covered with a waxy coating that provides a physical barrier of protection from the environment. Glossy mutants are deficient for this waxy coat and are common in crop varieties of Brassica oleracea closely related to broccoli, including cabbage, kale, cauliflower, Brussels sprouts, and collard. Glossy mutants have been recognized for a long time, but the genetic basis of this trait remains unknown. Glossiness is of particular interest because it can confer resistance to predation by several economically devastating insect pests like specific caterpillars and whiteflies. USDA scientists in Charleston, SC, used DNA sequencing techniques to identify genetic differences between broccoli lines that differ only for glossiness. The identified genetic differences are of special interest to entomologists working with crops of this species who are trying to learn more about how insects feed on them, and also of interest to scientists studying wax synthesis in Brassicas in particular and plants in general.

Technical Abstract: Wild-type Brassica oleracea L. have matte blue-green leaves caused by an interaction between leaf pigmentation and a waxy bloom coating the surface. Glossy mutants have reduced and/or altered epicuticular wax giving the leaves a shiny green appearance and have been identified in most B. oleracea crop varieties, including cauliflower, kale, broccoli, Brussels sprouts, cabbage, and collard. The genetic basis of glossy mutants has not been studied in B. oleracea. Glossiness can confer resistance to multiple herbivores mediated by modification of herbivore feeding behavior and foraging efficiency of their predators. The USDA, ARS, U.S. Vegetable Laboratory in Charleston, SC, released two pairs of near-isogenic broccoli lines (NILs) that visibly differ only for glossiness, providing ideal germplasm for the genetic study of epicuticular wax in B. oleracea. Genotyping-by-sequencing (GBS) resulted in hundreds of polymorphisms between each pair of NILs. Polymorphisms were identified in or near three different wax synthesis genes suggesting the two glossy mutants were caused by alteration of different steps of the pathway.