Issue link: http://winesandvines.uberflip.com/i/59079
More than 10,000 grape rootstock seedlings have been screened for resistance to the tougher nematodes. GRAPE GRO WING loxera, since the rootstock has Vitis vinifera in its parentage. Newer rootstocks that Dr. Walker is breeding are fairly resistant to Xiphenema index feeding, but it isn't clear whether they will prevent fanleaf degenera- tion infections. Both Vitis rufotomentosa and Muscadinia rotundifolia are the princi- pal sources of resistance to Xiphenema in- dex in the parentage of the rootstock. GRN 1 and GRN 5 are particularly resistant. 3. Phylloxera Phylloxera-resistant rootstocks are well understood, and we have had effective se- lections in use for more than 100 years. Re- cent concerns about 101-14 and 5C center around the ability of phylloxera to feed on small roots and cause nodosities, or swell- ings. There has been no sign of tuberosi- ties, which are large lesions that indicate the rootstock is failing. However, drought conditions combined with the presence of phylloxera can cause great stress to the vines, and these two rootstocks should not be used where very dry conditions or limited water is likely to occur. Regulated deficit irrigation strategies should be used carefully if you are on either of these root- stocks and phylloxera is known to be pres- ent in the vineyard. Rootstocks resist root knot nematodes R oot knot nematodes (Meloidogyne sp.) are a major pest for grapevines in sandy soils, especially in california's San Joaquin Valley. the female nematodes penetrate the roots and cause characteristic swellings on the feeder roots. new resistant rootstocks developed by dr. Peter cousins (right) and the uSda look very promising. Matador and Minotar are hybrids between the rootstock 101-14, Vitis mustangensis and Vitis rupestris. king- fisher is a cross between riparia Gloire rootstock, Vitis champignii and Vitis rufotomentosa. these rootstocks completely suppress nematode reproduction and show zero nematode egg masses. all have performed well in field testing. rooting ranges from 70% to 100%, and grafting compatibility is good. their main resistance is against root knot nematodes and should be used when that is the main nematode species present. G.M. More than 10,000 grape rootstock seedlings have been screened for resistance to the tougher nematodes, according to the USDA Agricultural Re- search Service. Wines & Vines APRiL 2012 55 uSda aGricultural rESEarch SErVicE