Detection and genetic variation analysis of grapevine fanleaf virus (GFLV) isolates in China

Construction of an Infectious DNA Clone of Grapevine Geminivirus A Isolate GN and Its Biological Activity in Plants Analyzed Using an Efficient and Simple Inoculation Method

The pathogenicity of grapevine geminivirus A (GGVA), a recently identified DNA virus, to grapevine plants remains largely unclear. Here, we report a new GGVA isolate (named GGVAQN) obtained from grapevine 'Queen Nina' plants with severe disease symptoms. The infectious clone of GGVAQN (pXT-GGVAQN) was constructed to investigate its pathogenicity. Nicotiana benthamiana plants inoculated with GGVAQN by agroinfiltration displayed upward leaf curling and chlorotic mottling symptoms. A simple, quick, and efficient method for delivering DNA clones of GGVAQN into grapevine plants was developed, by which Agrobacterium tumefaciens cells carrying pXT-GGVAQN were introduced into the roots of in vitro-grown 'Red Globe' grape plantlets with a syringe. By this method, all 'Red Globe' grape plants were systemically infected with GGVAQN, and the plants exhibited chlorotic mottling symptoms on their upper leaves and downward curling, interveinal yellowing, and leaf-margin necrosis symptoms on their lower leaves. Our results provide insights into the pathogenicity of GGVA and a simple and efficient inoculation method to deliver infectious viral clones to woody perennial plants.

Development of a Full-Length Infectious cDNA Clone of the Grapevine Berry Inner Necrosis Virus

Grapevine berry inner necrosis virus (GINV) belongs to the genus Trichovirus in the family Betaflexiviridae. The GINV isolate LN_BETA_RS was obtained from a “Beta” grapevine (Vitis riparia × Vitis labrusca) exhibiting chlorotic mottling and ring spot in Xingcheng, Liaoning Province, China. To verify the correlation between GINV and grapevine chlorotic mottling and ring spot disease, we constructed an infectious cDNA clone of GINV isolate LN_BETA_RS using the seamless assembly approach. Applied treatments of agroinfiltration infectious cDNA confirmed systemic GINV infection of the Nicotianaoccidentalis 37B by reverse transcription polymerase chain reaction (RT-PCR) and transmission electron microscopy, exhibiting chlorotic mottling symptoms on leaves. Infectious cDNA was also transmitted to new healthy N. occidentalis plants through rub-inoculation. Moreover, the cDNA clone was agroinfiltrated into “Beta” and “Thompson Seedless” grapevine plantlets, and the inoculated grapevines exhibited leaf chlorotic mottling and ringspot during the two years of observation. GINV-inoculated “Beta” grapevines had serious leaf chlorotic mottling and ringspot symptoms on the whole plant, while relatively few symptoms were observed on the leaves of agroinoculated “Thompson Seedless” grapevines in early spring and only weak ring spot gradually appeared later in the top young leaves. Our experiments fulfilled Koch’s postulates and revealed the causative role of GINV in grapevine chlorotic mottling and ring spot disease.

Occurrence and Genetic Diversity of Grapevine berry inner necrosis virus from Grapevines in China

To investigate the prevalence and genetic diversity of Grapevine berry inner necrosis virus (GINV) in China, 195 grapevine samples from 15 Chinese provinces and regions were tested using reverse-transcription polymerase chain reaction. The samples included symptomatic and asymptomatic cultivars, with 35.9% (70 of 195) of samples testing positive for GINV. Seventeen samples had obvious ring spot symptoms, and 94.1% (16 of 17) tested positive for GINV, suggesting that GINV may be highly associated with the ring spot symptom. The genetic diversity of GINV isolates was analyzed based on the partial nucleotide and amino acid sequences of the coat protein (CP) and movement protein (MP) genes. Phylogenetic analyses of the MP and CP gene sequences divided the GINV isolates into three groups. The majority of the Chinese isolates were in groups 1 and 2, and only one Chinese isolate, along with a previously reported Japanese isolate, was in group 3. This is the first report on the genetic diversity of GINV isolates and their prevalence and distribution in China.