Root-knot nematodes are a chief pest of vineyards across California and the United States, but aggressive and virulent nematode populations can feed on and damage many important rootstock varieties. The USDA-ARS breeding program tests the root-knot nematode resistance of rootstocks and wild grape species and combines nematode resistance and other useful traits through hybridization. We then evaluate the pest resistance, viticultural performance, and other important qualities of the new seedlings to identify candidate rootstocks.

Three improved root-knot nematode resistant rootstocks: Matador, Minotaur and Kingfisher were released from the USDA ARS breeding program in 2010 and are available from FPS. Matador and Minotaur resulted from selection of seedlings in a population derived from controlled hybridization of the Vitis hybrid rootstock 101-14 Mgt (seed parent) with the Vitis hybrid rootstock selection 3-1A (pollen parent). 3-1A is a cross of V. mustangensis and V. rupestris. Matador and Minotaur are full sibling rootstocks, with the same seed and pollen parent. Matador and Minotaur are easily rooted from dormant cuttings and bench grafted to Vitis vinifera scions. Matador was identified as a seedling selection on July 15, 2002 and Minotaur was identified as a seedling selection on July 2, 2002 due to their complete suppression of root-knot nematode reproduction in greenhouse evaluation.

The nematode population used to evaluate resistance was an N-virulent nematode population capable of feeding on and damaging N-allele grapevine rootstocks, such as Harmony and Freedom. Root-knot nematode resistance was confirmed in replicated tests of cutting grown plants. Dormant cuttings collected from plants grown in a California vineyard were evaluated for rooting ability: 73 percent of dormant cut-tings of Matador successfully propagated and produced callus, shoots, and roots; and 92 percent of dormant cuttings of Minotaur successfully propagated and produced callus, shoots, and roots. Matador and Minotaur were grafted to Syrah and planted into a rootstock trial at UC KREC, Parlier, Calif., in 2005.

Four years of fruiting data

When four years of fruiting data and three years of pruning weight data are considered, vines grafted on Matador rootstock showed a fruit to pruning weight ratio of 9.43; and vines grafted on Minotaur rootstock showed a fruit to pruning weight ratio of 8.84. The check rootstock, Freedom, showed a fruit to pruning weight ratio of 6.14, demonstrating the improved production efficiency of Matador and Minotaur rootstock compared to Freedom. Kingfisher resulted from selection of a seedling in a population derived from controlled hybridization of the Vitis hybrid rootstock selection 4-12A (seed parent) with Vitis riparia (pollen parent). 4-12A is a cross of V. x champinii Dog Ridge and V. rufotomentosa. The original Kingfisher vine was planted in 2002. In addition to nematode resistance and propagation evaluations, Kingfisher has been evaluated grafted to Syrah in a rootstock trial in California. Kingfisher is easily rooted from dormant cuttings and bench grafted to Vitis vinifera scions. Kingfisher was identified as a seedling selection on December 24, 2002 due to its complete suppression of root-knot nematode reproduction in greenhouse evaluation.

Root-knot nematode resistance was confirmed in replicated tests of cutting grown plants. The nematode population used to confirm resistance was an N-virulent nematode population capable of feeding on and damaging N-allele grapevine rootstocks, such as Harmony and Freedom. Dormant cuttings collected from plants grown in a California vineyard were evaluated for rooting ability; 100 percent of dormant cuttings of Kingfisher successfully propagated and produced callus, shoots, and roots. Kingfisher was grafted to Syrah and planted into a rootstock trial at UCKREC, Parlier, Calif., in 2005.

When four years of fruiting data and three years of pruning weight data are considered, King-fisher rootstock showed a fruit to pruning weight ratio of 6.53. The check rootstock, Freedom, showed a fruit to pruning weight ratio of 6.14, demonstrating the improved production efficiency of Kingfisher rootstock compared to Freedom. Minotaur, Matador, and Kingfisher rootstocks were bred by USDA-ARS as a part of a research project that received grant funding from the American Vineyard Foundation, California Table Grape Commission, California Raisin Marketing Board, California Grape Rootstock Improvement Commission, and California Grape Rootstock Research Foundation in addition to appropriated funds. These three rootstocks were released as public varieties, with no intellectual property protection.

Peter Cousins, Grape Rootstock Breeder and Geneticist, USDA ARS Grape Genetics Research Unit, Geneva, New York.