Selected grape rootstock trials from 5 to 22 years in age were evaluated around California. In these trials mixtures of nematode species had built up giving us an opportunity to validate our previous data from microplot settings. Data from four to five replicates were collected from each site. Many trials had at least 10 rootstocks. A few had only two or three but were older, thus making them worthwhile to sample. We eventually collected samples from 15 sites in Kern County, three in Fresno County, three in Monterey County, one each from Sonoma, Mendocino and Merced counties, and will be sampling one from San Joaquin County. The nematode data from more than 1,100 soil samples are still being analyzed but attached are two charts showing our method for comparing field data with existing microplot data in sites where Xiphinema index was present. This work is tedious and expensive and my concern is that the payoff may not be as great as other studies we hope to conduct in the future. The major problem is that even when rootstock trials are 5 years old and the nematodes are not yet evenly distributed across replicates, resulting in false negatives. Nonfumigated sites such as the field in Mendocino on Chart 2 did not help to clarify. The Mendocino field did not have an own-rooted comparison but we are able to “guesstimate” based on the populations on 3309. There were also advantages to this work. The primary advantage was the opportunity to sample sites with mixed populations where nematodes may be competing with one another or other soil microbes. We have learned that 1103P is too good a host for X. index but remain unclear on 110R and 101-14. Root knot nematode resistance in Freedom and Harmony was nonexistent in two of three older trials in Fresno County, although their tolerance to the nematode and extreme vigor has kept them from declining below the own-rooted. The field-derived data do appear to validate our previous microplot work. VR 039-16 is supporting X. index in one replicate of Kern County and at a separate field site in Monterey. This needs further investigation.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF1995-11-16 13:50:532017-11-16 14:12:29Nematode Evaluation of Eight Rootstocks Present in Existing Field Trials