The primary goal of this proposal is to develop novel regeneration technologies needed to engineer walnut rootstocks for pest and disease resistance. The productivity of the walnut industry of California is dependent the availability of superior rootstocks to combat soil disease and pest problems. Individual selections displaying resistance to either Phytophthora crown and root rots or to root ...

The objectives of this research are: (1) to evaluate elite Paradox hybrid clones for resistance to Phytophthora citricola, a virulent and prevalent crown and root pathogen affecting California walnuts and (2) to determine specific etiology of a root and crown rot problem in upper Sacramento Valley orchards on Paradox walnut rootstock. Two screens for resistance to P. citricola were completed in...

During surveys of dying vegetation in natural ecosystems and associated waterways in Australia many new taxa have been identified from Phytophthora ITS Clade 6. For representative isolates, the region spanning the internal transcribed spacer region of the ribosomal DNA, the nuclear gene encoding heat shock protein 90 and the mitochondrial cox1 gene were PCR amplified and sequenced. Based on phy...

A novel Phytophthora species was frequently recovered from irrigation reservoirs at several ornamental plant production facilities in eastern Virginia. Initial sequencing of the internal transcribed spacer (ITS) region of this species generated unreadable sequences due to continual polymorphic positions. Cloning and sequencing the ITS region as well as sequencing the mitochondrially encoded cyt...

The primary goal of the Walnut Improvement Program, which was initiated in 1982 as a cooperative effort between USDA-ARS and U.C. Davis, is to develop germplasm with increased resistance or tolerance to the two major diseases limiting commercial production of Persian walnuts. These are the blackline and the Phytophthora root and crown rot diseases. Also under the auspices of this program are th...

Despite its association with important agricultural crops, Phytophthora clade 8b is a poorly studied group of species. The clade currently consists of three officially described species (Phytophthora porri, P. brassicae and P. primulae) that are host-specific pathogens of leek, cabbages and Primula spp., respectively. However, over the past few decades, several other clade 8b-like Phytophthoras...

ABSTRACT In New Jersey, Phytophthora cinnamomi is the pathogen most commonly isolated from diseased roots and runners of the cultivated cranberry (Vaccinium macrocarpon). A second distinct species of Phytophthora has been isolated from dying cranberry plants and surface irrigation water. This species is homothallic with paragynous antheridia and ellipsoid-limoniform, nonpapillate sporangia. It ...