Prevalence and Genetic Diversity of Grabloviruses in Free-Living Vitis spp.

Abstract

The distribution and diversity of grapevine red blotch virus (GRBV) and wild Vitis virus 1 (WVV1) (genus Grablovirus; family Geminiviridae) were determined in free-living Vitis spp. in northern California and New York from 2013 to 2017. Grabloviruses were detected by polymerase chain reaction in 28% (57 of 203) of samples from California but in none of the 163 samples from New York. The incidence of GRBV in free-living vines was significantly higher in samples from California counties with high compared with low grape production (χ = 83.09; P < 0.001), and in samples near (<5 km) to compared with far (>5 km) from vineyards (χ = 57.58; P < 0.001). These results suggested a directional spread of GRBV inoculum predominantly from vineyards to free-living Vitis spp. WVV1 incidence was also significantly higher in areas with higher grape production acreage (χ = 16.02; P < 0.001). However, in contrast to GRBV, no differential distribution of WVV1 incidence was observed with regard to distance from vineyards (χ = 0.88; P = 0.3513). Two distinct phylogenetic clades were identified for both GRBV and WVV1 isolates from free-living Vitis spp., although the nucleotide sequence variability of the genomic diversity fragment was higher for WWV1 (94.3 to 99.8% sequence identity within clade 1 isolates and 90.1 to 100% within clade 2 isolates) than GRBV (98.3% between clade 1 isolates and 96.9 to 100% within clade 2 isolates). Additionally, evidence for intraspecific recombination events was found in WVV1 isolates and confirmed in GRBV isolates. The prevalence of grabloviruses in California free-living vines highlights the need for vigilance regarding potential grablovirus inoculum sources in order to protect new vineyard plantings and foundation stock vineyards in California.

Transmission of Grapevine Red Blotch Virus by Spissistilus festinus [Say, 1830] (Hemiptera: Membracidae) between Free-Living Vines and Vitis vinifera ‘Cabernet Franc’

“…GRBV has also been reported in Switzerland [19], South Korea [20], Mexico [21], Argentina [22], India [23], Italy [24], and France [25]. The global reach of GRBV can be attributed to the dissemination of infected planting materials, while secondary spread in U.S. states, such as California [3,26,27] and Oregon [28,29], as well as the province of British Columbia in Canada [16], is ascribed to an insect vector. There is no evidence of secondary spread in New York [27], Switzerland [19], or France [25].…”

“…In vineyards where secondary spread is documented, spatiotemporal increase patterns of GRBV-infected vines point to the presence of an aerial hemipteran vector [3,16,[26][27][28][29]. Of the few vector candidates identified in a diseased 'Cabernet franc' vineyard in Napa County in northern California, Spissistilus festinus [Say, 1830] (Hemiptera: Membracidae), the three-cornered alfalfa hopper, proved to be the most likely candidate [3] and was subsequently reported to vector GRBV [30,31].…”

“…In addition to Vvin, rootstock genotypes [2,3], interspecific hybrids [34], and Muscadine grapes [15], GRBV has been found in free-living vines in northern California [26,31,35,36] and southern Oregon [29]. In contrast, the virus was not detected in free-living vines in New York [26].…”

“…In addition to Vvin, rootstock genotypes [2,3], interspecific hybrids [34], and Muscadine grapes [15], GRBV has been found in free-living vines in northern California [26,31,35,36] and southern Oregon [29]. In contrast, the virus was not detected in free-living vines in New York [26]. These findings suggested that free-living vines could serve as GRBV inoculum sources in northern California and southern Oregon, although, unlike for Vvin cultivars, free-living vines sustain latent infections [26,29].…”

“…These findings suggested that free-living vines could serve as GRBV inoculum sources in northern California and southern Oregon, although, unlike for Vvin cultivars, free-living vines sustain latent infections [26,29]. Given that one of the previous surveys of free-living vines in northern California targeted plants that were at least 100 m apart [26], an aerial hemipteran vector is likely involved in GRBV spread within populations of freeliving vines. We hypothesized that S. festinus can transmit GRBV between free-living and wine grape cultivars.…”