Development, testing, and introduction of Grape Rootstalks with broad and durable nematode resistance

We continue toward our goal of developing grape rootstocks with broad and durable
resistance to nematode species that are important in California vineyards. Few of the
currently available grape rootstocks have resistance to more than one nematode species.
In previous years, we have screened rootstock candidates against the root knot nematode
(Meloidogyne incognita race 3), two strains of root-knot nematode that overcome the
resistance of Harmony rootstock (Meloidogyne arenaria strain A and Meloidogyne
incognita strain C), and the dagger nematode (Xiphinema index). Fourteen rootstock
candidates exhibit broad resistance to those nematodes. This year, we continued to test
the breadth of that resistance beyond the range of the primary screen species by
evaluating the resistance of the 14 candidates to the ring nematode, Mesocriconema
xenoplax. Only one of the rootstock candidates exhibited any resistance to the ring
nematode and we are looking for new sources of resistance. We also continued to test the
durability of nematode resistance of the rootstock candidates when they are exposed to
combinations of nematode species, including species such as the ring nematode for which
they are hosts. We extended and repeated, using greater precision of temperature control,
experiments to determine the durability of resistance at different temperatures.
Resistance of several of the rootstock candidates to several root-knot nematode variants
was compromised at soil temperatures of 30°C and above but appeared durable at 27°C
and below. Resistance to Xiphinema index was not compromised by soil temperature in
any of the rootstock candidates. Field testing of the rootstock candidates continues in
fields that were heavily infested with root-knot nematodes. Nematode population levels
are declining in the root-zones of all rootstock candidates, indicating that reproduction of
the nematode is not occurring.