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United States Department of Agriculture

Agricultural Research Service


Location: Grape Genetics Research

2012 Annual Report

1a. Objectives (from AD-416):
1. Determine some of the key genetic factors controlling environmental adaptation and fruit quality differences among cultivated grapes and between cultivated and wild grapes. 1A. Identify molecular markers tightly linked to QTL controlling phenotypic variation in grape for environmental adaptation and fruit quality. 1B. Identify candidate genes for environmental adaptation through characterization of differences in gene content and global gene expression among wild grapes with divergent phenotypes. 2. Develop grape germplasm with novel phenotypes for fruit quality traits.

1b. Approach (from AD-416):
The objectives will be accomplished by applying genetic and genomic tools and research strategies, including populations and marker development, dissection of complex phenotypes, QTL mapping, gene expression analysis, and mutagenesis. Genetic linkage maps will be contructed from populations segregating for economically important traits. Genetic dissection of traits will be conducted in populations derived from bi-parental crosses as well as diverse cultivated and wild grape germplasm.

3. Progress Report:
Irradiation-induced mutations are an important source of variation for crop improvement. Recently we have established an embryogenic cell suspension system for mutagenesis study and induction of mutations. The system can allow us to generate hundreds of clonal plants in a very short time. By using the system, we have generated several hundreds of mutant plants derived from gamma-ray-treated cell suspension cultures of Vitis vinifera cv. Chardonnay. These mutant plants will be analyzed and screened for novel traits important for Chardonnay improvement. Grapevines grown in many regions of the Eastern United States are poorly adapted to low-temperature and frequently damaged by severe winters and fluctuating temperature during the spring and fall. There is tremendous variation among cultivated and wild grapes for tolerance to low-temperature stress, including some types that are substantially more tolerant to freezing than the primary cultivated species. In FY12 we assessed 32 wild and cultivated germplasm accessions for variation in the phenotypes of chilling hour requirement, dormancy fulfillment, and heating hour requirement. Variation in soluble carbohydrate levels, a trait hypothesized to be related to mid-winter freezing tolerance, was measured from over 2400 dormant buds, representing 40 different genotypes and two cold tolerance mapping populations. Finally, genetic variation was examined within a Vitis diversity panel of 190 wild and cultivated grapevine genotypes for 11 candidate cold tolerance genes. Muscadine grapes are a regionally important fruit crop in the southern United States. Genetic information on the inheritance of economically important traits of muscadine grapes is minimal. In order to provide genetic information useful to muscadine grape breeders, a project was initiated to genetically map many fruit quality traits in two grapevine populations maintained by the University of Arkansas’s fruit breeding program. In FY12, genetic maps were constructed for these two populations and some initial phenotypic data was collected for flower type and berry color. Grape aroma is a primary determinant of table grape, unfermented juice, and wine quality. In collaboration with the University of British Columbia a project was continued to conduct an association genetics screen for grape aroma in a subset of the USDA grape germplasm collection. In FY12 a genome-wide association analysis was completed to elucidate genetic components underlying variation in the content of several aromatic compounds from fruit samples collected in previous years from over 300 different grapevine varieties maintained by USDA.

4. Accomplishments
1. Localized the genomic position of genes controlling the production of methoxypyrazines, a key component of grape varietal aroma. Meothoxypyrazines are a class of volatile aromatic compounds that are commonly produced in grape varieties traditionally grown in Bordeaux, such as Cabernet Sauvignon, and Sauvignon Blanc. At moderate to low levels, these compounds are considered a desirable and key component of wines produced from these grapes. However, at high concentrations, these compounds are considered un-desirable and lead to wines that are excessively vegetal in their aromatic profile. To understand the genetic control of the production of these traits, an experimental grapevine population that was generated from vines differing in the production of these compounds was used to map the genomic location of genes underlying the variation. Variation in this trait was shown by ARS researchers at Geneva, New York to be quantitatively inherited, and controlled by 2 non-linked genes with large genetic effects. The mapping of this trait is the first step in developing an assay that will improve the selection efficiency within grape breeding programs for this trait and will lead to further insights into the production of these compounds in developing berries.

Review Publications
Liang, Z., Zhao, S., Ma, A., Zhong, G., Li, S. 2011. Inheritance of sugar and acid contents in the ripe berries of a tetraploid x diploid grape cross population. Journal of Euphytica. 182:251-259.

Last Modified: 06/25/2017
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