Economic Studies Reinforce Efforts to Safeguard Specialty Crops in the United States.

Pathogen-tested foundation plant stocks are the cornerstone of sustainable specialty crop production. They provide the propagative units that are used to produce clean planting materials, which are essential as the first-line management option of diseases caused by graft-transmissible pathogens such as viruses, viroids, bacteria, and phytoplasmas. In the United States, efforts to produce, maintain, and distribute pathogen-tested propagative material of specialty crops are spearheaded by centers of the National Clean Plant Network (NCPN). Agricultural economists collaborated with plant pathologists, extension educators, specialty crop growers, and regulators to investigate the impacts of select diseases caused by graft-transmissible pathogens and to estimate the return on investments in NCPN centers. Economic studies have proven valuable to the NCPN in (i) incentivizing the use of clean planting material derived from pathogen-tested foundation plant stocks; (ii) documenting benefits of clean plant centers, which can outweigh operating costs by 10:1 to 150:1; (iii) aiding the development of disease management solutions that are not only ecologically driven but also profit maximizing; and (iv) disseminating integrated disease management recommendations that resonate with growers. Together, economic studies have reinforced efforts to safeguard specialty crops in the United States through the production and use of clean planting material.

A Synoptic Analysis of the Temporal and Spatial Aspects of Grapevine Leafroll Disease in a Historic Napa Vineyard and Experimental Vine Blocks.

Five Grapevine leafroll-associated virus 3 (GLRaV-3) epidemics were analyzed utilizing a standardized approach to robustly characterize the temporal and spatial parameters. Published data included in the analysis are from Spain, New Zealand, and Napa Valley, CA together with new data from a historic vineyard in Napa Valley, CA. Linear regression analyses of logit-transformed incidence data indicated a maximum average increase of 11% per year in disease incidence, with considerable variation among locations. Spatial analyses, including distribution fitting, examination of the effective sample size, and evaluation of the parameters of the binary power law fitted to variance data for disease incidence, indicated a high degree of consistency among the data sets. In all cases, except at very low disease incidence, a high degree of spatial aggregation was noted, with evidence that the degree of aggregation varied as a function of mean disease incidence. The polyetic dynamics of disease follow a logistic-like pattern over multiple seasons, consistent with limitation by inoculum availability (infected vines) at low incidence and limitation by disease-free vines at high incidence.

Vitis californica and Vitis californica × Vitis vinifera Hybrids are Hosts for Grapevine leafroll-associated virus-2 and -3 and Grapevine virus A and B.

Vitis and non-Vitis spp. surrounding nine Napa Valley vineyards were surveyed for Grapevine leafroll-associated virus (GLRaV)-1 to -5 and -9, Grapevine virus A (GVA), Grapevine virus B (GVB), and Grapevine virus D (GVD). Vitis spp. from three riparian areas not adjacent to vineyards were also included. DNA fingerprinting and probability analyses indicated that the Vitis samples consisted primarily of Vitis californica followed by V. californica × V. vinifera hybrids. Single and mixed infections of GLRaV-2, -3, GVA, or GVB were detected by conventional or quantitative reverse-transcription polymerase chain reaction in 6 of the 66 V. californica and 11 of the 19 V. californica × V. vinifera hybrids. GLRaV-1, -4, -5, -9, and GVD were not detected. Phylogenetic analysis of GLRaV-2 and -3 partial coat protein gene nucleotide sequences indicated that the isolates from V. californica and V. californica × V. vinifera hybrids were closely related to isolates from V. vinifera.

Nucleotide sequence and rt-PCR detection of a virus associated with grapevine rupestris stem-pitting disease.

ABSTRACT Grapevine rupestris stem pitting (RSP) is a graft-transmissible disease of unknown etiology. We have characterized a virus associated with this disease. The entire genomic sequence (GenBank accession number AF026278) consisted of 8,725 nucleotides excluding a poly(A) tail. Six open reading frames (ORF) were found. ORF1 potentially encodes a polypeptide with a methyltransferase domain, a papain-like proteinase domain, a helicase domain, and a RNA-dependent RNA polymerase domain; ORF2, ORF3, and ORF4 compose a triple-gene block; ORF5 encodes a coat protein; and ORF6 is located near the 3' end with unknown function. Sequence analysis indicated that the virus is most similar to apple stem-pitting virus and may be allied with the carla- and potexviruses and grouped with other viruses that infect woody hosts. A specific reverse-transcription polymerase chain reaction (RT-PCR)-based detection method was developed. Among 62 grapevine sources known to be infected with rupestris stem-pitting disease, 60 sources tested positive by RT-PCR. Among 43 healthy vines tested, all were negative. The name grapevine rupestris stem-pitting-associated virus is proposed.

First Report of Grapevine Kober Stem Grooving in the United States.

The last decade has brought extensive new plantings of grapevines (Vitis vinifera L.) to California vineyards. In some vineyards, severe viruslike problems have been observed (2). To ascertain possible causal agent(s), extensive testing for grapevine viruses was initiated. Testing included a 2-year woody index on indicators V. rupestris cv. Saint George, LN 33, V. vinifera cv. Cabernet Franc, and Kober 5BB. To our knowledge, this is the first field survey for grape virus diseases in the United States that includes woody indexing on Kober 5BB, a relatively new indicator for the grapevine rugose wood diseases (1). A Sonoma County field selection of Sauvignon Blanc grafted to the rootstock Freedom was included in these tests; the 2-year-old vines exhibited stunting, leaf rolling, leaf yellowing, wood necrosis, and pitting symptoms at the graft union. When indexed on the four indicators, the following disease symptoms were observed: stem pitting on V. rupestris; corky bark on LN 33; leafroll on Cabernet Franc; and stem grooving on Kober 5BB. An enzyme-linked immunosorbent assay confirmed the presence of grapevine leafroll-associated viruses 2, and 3, as well as Grapevine Virus A, which is associated with Kober stem grooving. The Sauvignon Blanc selection appears to be infected with several grapevine viruses, as is often the case when virus symptoms in vineyards are severe. Among these disease agents, only Kober stem grooving is reported to cause the severe pitting and grooving symptoms observed on the indicator Kober 5BB (1). This is the first report of Kober stem grooving in the United States. References: (1) R. Garau et al. Vitis 33:161, 1994. (2) D. A. Golino. Am. J. Enol. Vitic. 44:148, 1993.

Common identity of grapevine viroids from USA and Australia revealed by PCR analysis.

Pairs of viroid-specific oligonucleotide primers were selected and used in separate reverse transcription reactions coupled with the polymerase chain reaction to obtain DNA products of predetermined sizes characteristic of each viroid. The reaction conditions allowed efficient incorporation of small amounts of 32P-dATP which enabled rapid detection of the products in polyacrylamide gels. Using this method as well as probe hybridization, the presence of grapevine yellow speckle viroids 1 and 2 (previously known as GV1B) in grapevine samples from California was demonstrated, and it was established that the Australian grapevine viroid occurs in California. These comparisons provide the basis for uniform nomenclature of grapevine viroids found in different geographical regions.