Spatio-Temporal Spread of Grapevine Leafroll Disease in Washington State Vineyards.

The spread of grapevine leafroll disease (GLD) to vineyards planted with certified planting stock is of significant concern to grape growers. In this study, the spatial and temporal spread of GLD was examined in three vineyard blocks planted with virus-tested wine grape (Vitis vinifera) cultivars adjacent to vineyard blocks heavily infected with GLD in two geographic locations in eastern Washington State. During each season, the position of vines showing GLD symptoms was recorded in a matrix representing the planting lattice. Symptomatic vines were positive only for Grapevine leafroll-associated virus 3 (GLRaV-3), the most common virus species consistently associated with GLD in Washington vineyards. The results from multiple seasons showed a gradual increase in disease incidence over time in all three blocks. Spatial and temporal mapping of GLD indicated a disease gradient in which the highest percentage of symptomatic vines was in rows proximal to infected old blocks. Spatial autocorrelation analysis using Moran's I values suggested random patterns of symptomatic vines in the three blocks during initial years, indicating primary spread of the virus not related to infected vines within the block. Clustering at the scale of neighboring vines during subsequent years suggested secondary spread within the block. Results of quadrat-based spatial analyses of GLD incidence were compared with previously reported data obtained from California and elsewhere for an improved understanding of the dynamics of GLD spread to facilitate area-wide disease management strategies.

Gene flow in commercial alfalfa (Medicago sativa subsp. sativa L.) seed production fields: Distance is the primary but not the sole influence on adventitious presence.

In insect-pollinated crops, gene flow is affected by numerous factors including crop characteristics, mating system, life history, pollinators, and planting management practices. Previous studies have concentrated on the impact of distance between genetically engineered (GE) and conventional fields on adventitious presence (AP) which represents the unwanted presence of a GE gene. Variables other than distance, however, may affect AP. In addition, some AP is often present in the parent seed lots used to establish conventional fields. To identify variables that influence the proportion of AP in conventional alfalfa fields, we performed variable selection regression analyses. Analyses based on a sample-level and a field-level analysis gave similar, though not identical results. For the sample-level model, distance from the GE field explained 66% of the variance in AP, confirming its importance in affecting AP. The area of GE fields within the pollinator foraging range explained an additional 30% of the variation in AP in the model. The density of alfalfa leafcutting bee domiciles influenced AP in both models. To minimize AP in conventional alfalfa seed fields, management practices should focus on optimizing isolation distances while also considering the size of the GE pollen pool within the pollinator foraging range, and the foraging behavior of pollinators.

The Relative Occurrence of Grapevine leafroll-associated virus 3 and Grapevine red blotch virus in Washington State Vineyards.

Vineyard surveys were conducted for three consecutive seasons in eastern Washington State, the major grapevine-growing region in the state, to document the occurrence of Grapevine leafroll-associated virus 3 (GLRaV-3) and Grapevine red blotch virus (GRBV). The majority of samples were collected from red-berried wine grape (Vitis vinifera) cultivars exhibiting symptoms of or suspected for grapevine leafroll (GLD) and red blotch (GRBD) diseases. A limited number of samples from white-berried cultivars were collected randomly due to the lack of visual symptoms. Samples were collected from a total of 2,063 grapevines from 18 red-berried cultivars and seven white-berried cultivars planted in eight American Viticultural Areas and tested for GLRaV-3 and GRBV using RT-PCR and PCR, respectively. The results showed 67.77% and 6.01% of total samples positive for GLRaV-3 and GRBV, respectively, and 9.06% of samples positive for both viruses. About 17% of samples tested negative for the two viruses, but some of these samples were positive for GLRaV-2 and GLRaV-4. Overall results indicated that GLRaV-3 was more common than GRBV, independent of cultivars and the geographic origin of samples. Due to variability in symptoms in red-berried cultivars, virus-specific diagnostic assays were deemed necessary for reliable identification of GLRaV-3 and GRBV and to differentiate GLD and GRBD symptoms from those induced by biotic and abiotic stresses in vineyards. A multiplex PCR protocol was developed for simultaneous detection of GLRaV-3 and GRBV in grapevine samples. A global phylogenetic analysis of GRBV genome sequences revealed segregation of virus isolates from Washington State vineyards into two distinct clades, with the majority of isolates belonging to clade II.

Migratory Bee Hive Transportation Contributes Insignificantly to Transgenic Pollen Movement Between Spatially Isolated Alfalfa Seed Fields.

Contracted commercial beekeeping operations provide an essential pollination service to many agricultural systems worldwide. Increased use of genetically engineered crops in agriculture has raised concerns over pollinator-mediated gene flow between transgenic and conventional agricultural varieties. This study evaluated whether contracted migratory beekeeping practices influence transgenic pollen flow among spatially isolated alfalfa fields. Twelve honey bee (Apis mellifera L.) colonies were permitted to forage on transgenic alfalfa blossoms for 1 wk in Touchet, WA. The hives were then transported 112 km to caged conventional alfalfa plots following one and two nights of isolation (8 and 32 h, respectively) from the transgenic source. Alfalfa seed harvested from the conventional plots was assessed for the presence of the transgene using a new seedling germination assay. We found that 8 h of isolation from a transgenic alfalfa source virtually eliminated the incidence of cross-pollination between the two varieties.

Occurrence of Transgenic Feral Alfalfa (Medicago sativa subsp. sativa L.) in Alfalfa Seed Production Areas in the United States.

The potential environmental risks of transgene exposure are not clear for alfalfa (Medicago sativa subsp. sativa), a perennial crop that is cross-pollinated by insects. We gathered data on feral alfalfa in major alfalfa seed-production areas in the western United States to (1) evaluate evidence that feral transgenic plants spread transgenes and (2) determine environmental and agricultural production factors influencing the location of feral alfalfa, especially transgenic plants. Road verges in Fresno, California; Canyon, Idaho; and Walla Walla, Washington were surveyed in 2011 and 2012 for feral plants, and samples were tested for the CP4 EPSPS protein that conveys resistance to glyphosate. Of 4580 sites surveyed, feral plants were observed at 404 sites. Twenty-seven percent of these sites had transgenic plants. The frequency of sites having transgenic feral plants varied among our study areas. Transgenic plants were found in 32.7%, 21.4.7% and 8.3% of feral plant sites in Fresno, Canyon and Walla Walla, respectively. Spatial analysis suggested that feral populations started independently and tended to cluster in seed and hay production areas, places where seed tended to drop. Significant but low spatial auto correlation suggested that in some instances, plants colonized nearby locations. Neighboring feral plants were frequently within pollinator foraging range; however, further research is needed to confirm transgene flow. Locations of feral plant clusters were not well predicted by environmental and production variables. However, the likelihood of seed spillage during production and transport had predictive value in explaining the occurrence of transgenic feral populations. Our study confirms that genetically engineered alfalfa has dispersed into the environment, and suggests that minimizing seed spillage and eradicating feral alfalfa along road sides would be effective strategies to minimize transgene dispersal.