Author
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Ramming, David |
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Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/2/2010 Publication Date: 6/2/2010 Citation: Ramming, D.W. 2010. Greenhouse Screening of Grape Rootstock Populations to Determine Inheritance of Resistance to Phylloxera. American Journal of Enology and Viticulture. 61(2):234-239. Interpretive Summary: Phylloxera is one of the most important pests of grapes around the world. In the 1990’s many grapes were removed in Napa and Sonoma counties of California due to a new biotype of phylloxera. Rootstocks that are resistant to phylloxera are probably the best method to control the problem. Identifying resistant rootstocks takes a long time using field trials. Greenhouse methods reduce the time necessary to identify resistant types and can be used in breeding programs to make them more efficient. Information about inheritance of resistance to phylloxera would also make breeding programs more efficient. A very simple replicated method using 2 ¼” pots and leafy cuttings in the greenhouse was used to screen seedling populations in 6 to 8 weeks. High percentages of resistant offspring were generated from resistant parents as expected. However, Kober 5BB gave almost 100% resistant progeny even when crossed with susceptible rootstocks. It was the best for transmitting the highest percentage of resistant progeny. The segregation for phylloxera resistance could be explained by two complimentary dominant genes in most families. Technical Abstract: Phylloxera has been an important pest in California since their discovery in 1880 within Sonoma and Napa Counties. Phylloxera resistant rootstocks and germplasm were selected from American grape species native to the eastern United States. Breeding programs to develop improved phylloxera resistant rootstocks were started in the last part of the 19th century. Resistance to phylloxera has been reported to be controlled by several genes. To focus on one aspect of resistance to phylloxera, a greenhouse screening method was used to observe absence/presence of root nodosities produced by phylloxera. Only one source of phylloxera from Fresno County was used to reduce the complication of various biotypes. Grape rootstocks with known field reaction to Phylloxera were evaluated to test the reliability of the greenhouse test. A design II mating factorial cross was made between male and female rootstocks with a range of resistance to susceptibility. The reaction of their progeny to phylloxera was observed in the greenhouse. All populations segregated for resistance/susceptibility with a few exceptions. Dogridge crossed with two susceptible genotypes gave all susceptible offspring. Kober 5BB crossed with susceptible or resistant genotypes gave all resistant offspring. The segregation of resistance to nodosity development could be explained by two complimentary dominant genes in most families. |
