Good Fruit Grower / July 2012 / Nematode-­resistant grape ­rootstocks

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Nematode-­resistant grape ­rootstocks

The new Matador, Minotaur, and Kingfisher rootstocks are resistant to aggressive strains of root-knot nematodes.

ith the first three root-knot nematode-resistant rootstocks for grapes recently released by the U.S. Department of Agriculture, grape geneticist Dr. Peter Cousins is concentrating on the next round of resistant rootstocks to give growers options in matching rootstocks to vigor needs.

Root-knot nematodes (Meloidognyne spp.) are the primary nematode pest of vineyards across the country and cause more than $1 billion in damage annually, according to Cousins, who’s based at USDA’s Grape Genetics Research Unit housed in Cornell University’s Geneva, New York, ­experiment station.

In Washington State, both root-knot and dagger nematodes are the main nematode concerns, but across the country, more acres of U.S. vineyards have root-knot nematodes as the primary root pest than any other root pest, including phylloxera, Cousins said. Vines infested by the microscopic worms yield less and are less efficient at taking up nutrients and water from the soil.

His rootstock research currently only screens for root-knot nematodes because of funding and time limitations. Cousins can’t say one way or another if the new rootstocks are resistant to dagger or other species of nematodes because they haven’t been tested.

The need for improved grape rootstocks became apparent in the 1990s after phylloxera, a tiny aphid-like insect that feeds on grape roots, infested vineyards in Napa Valley and other California grape-growing regions. Widely planted rootstocks developed in the 1960s and 1970s were less resistant to phylloxera than expected, and thousands of vineyard acres had to be removed. Several phylloxera-resistant ­rootstocks have since been developed.

Cousins said that with several phylloxera-resistant rootstocks available, the priority has shifted to nematode resistance. “Finding root-knot nematode resistance is now the utmost priority of USDA’s grape ­rootstock improvement program.”

Nematodes have developed into a big problem since growers lost Nemacur (fenamiphos) in 2007 when Bayer Corporation voluntarily pulled its U.S. registration because of association with bird kills. Without Nemacur, grape growers no longer have an effective nematicide for already-established vineyards and only have a few somewhat effective preplant materials.

Before the recent USDA releases, a few rootstocks offered root-knot resistance, though not against virulent nematode populations, and they were faulted for other problems, including insufficient phylloxera resistance, sensitivity to other pests and diseases, or difficulty of propagation.

“But growers are in a much better position now than they were 20 years ago,” Cousins said in a phone interview with the Good Fruit Grower. Most Washington grape growers do not use rootstocks, preferring to plant own-rooted material because vines can easily be retrained in the event of winter damage. However, there may be more interest in rootstocks from growers in the future as pest- and disease-resistant rootstocks are ­developed.

New releases

The three improved root-knot–resistant rootstocks released in 2010 by USDA’s Agricultural Research Service are named Matador, Minotaur, and Kingfisher. Matador and Minotaur are full sibling rootstocks, resulting from the hybridization of the 101-14 Mgt rootstock and the 3-1A rootstock selection (a cross of Vitis mustangensis and V. rupestris). Kingfisher came from a cross of the Vitis hybrid rootstock selection 4-12A (V. x champinii Dog Ridge and V. rufotomentosa) with V. riparia. All three have better root-knot resistance than Freedom and Harmony rootstocks and are available from the Foundation Plant Services at the University of ­California, Davis.

Cousins, who joined USDA’s research station at Cornell University in 1999, is now part of the Grape Genetics Research Unit at Geneva established in 2005. The grape genetics unit is part of the National Plant Germplasm System that preserves and safeguards grapes, apples, tart cherries, and vegetables. Access to the germplasm is an ­essential tool for the breeding of new rootstocks.
Through the years, Cousins and his team have screened more than 10,000 rootstock seedlings in their search for nematode resistance.