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Fighting a Tougher Nematode 
The past decade has seen emergence of aggressive root knot nematodes (Meloidogyne spp.) that overcome the natural defense mechanisms of grape rootstocks such as Freedom and Harmony, which are known for their resistance to these microscopic worms. More than 10,000 grape rootstock seedlings have been screened for resistance to the tougher nematodes. Only those seedlings which completely suppress nematode feeding and reproduction and which yield zero nematode egg masses are selected. The seedlings are then propagated and planted. The goal is to develop and introduce rootstocks that are both resistant to the tougher nematodes and adaptable to California viticulture. More than 200 resistant selections have been planted in the vineyard and several selections are in vineyard trials.
A Different Gene Altogether
The N-gene in traditional grape rootstocks such as Freedom and Harmony has for decades conferred resistance to Meloidogyne. A new source of resistance that GGRU scientists discovered is not due to a variation of the N-gene, but a different gene altogether. There are now two known genes for root-knot nematode resistance in grapes. It may be possible to breed both genes into the same rootstock-a technique known as 'pyramiding'. This strategy could provide better protection if the two genes have complementary activity.
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