Abstract
Grapevine leafroll disease (GLD) is caused by a complex of several virus species (grapevine leafroll-associated viruses, GLRaV) in the family Closteroviridae. Because of its increasing importance, it is critical to determine which species of GLRaV is predominant in each region where this disease is occurring. A structured sampling design, utilizing a combination of RT-PCR based testing and sequencing methods, was used to survey GLRaVs in Napa Valley (California, USA) vineyards (n = 36). Of the 216 samples tested for GLRaV-1, -2, -3, -4, -5, and -9, 62% (n = 134) were GLRaV positive. Of the positives, 81% (n = 109) were single infections with GLRaV-3, followed by GLRaV-2 (4%, n = 5), while the remaining samples (15%, n = 20) were mixed infections of GLRaV-3 with GLRaV-1, 2, 4, or 9. Additionally, 468 samples were tested for genetic variants of GLRaV-3, and of the 65% (n = 306) of samples positive for GLRaV-3, 22% were infected with multiple GLRaV-3 variants. Phylogenetic analysis utilizing sequence data from the single infection GLRaV-3 samples produced seven well-supported GLRaV-3 variants, of which three represented 71% of all GLRaV-3 positive samples in Napa Valley. Furthermore, two novel variants, which grouped with a divergent isolate from New Zealand (NZ-1), were identified, and these variants comprised 6% of all positive GLRaV-3 samples. Spatial analyses showed that GLRaV-3a, 3b, and 3c were not homogeneously distributed across Napa Valley. Overall, 86% of all blocks (n = 31) were positive for GLRaVs and 90% of positive blocks (n = 28) had two or more GLRaV-3 variants, suggesting complex disease dynamics that might include multiple insect-mediated introduction events.
Highlights
The successful management and control of plant diseases is predicated on knowledge of disease etiology and epidemiology
Single infections of GLRaV-3 represented 81% of the samples, while 4% were single infections of GLRaV-2, and 15% were mixed infections of GLRaV-3 with either GLRaV-1, 2, 4, or 9
Surveys of plants with Grapevine leafroll disease (GLD) symptoms have shown that several GLRaV species are distributed throughout grape-growing regions of the world [4,8,10,26]
Summary
The successful management and control of plant diseases is predicated on knowledge of disease etiology and epidemiology. There are groups of pathogens that cause similar symptoms in plants and, as a consequence, the same outwardly apparent disease symptoms may have different etiological agents. Grapevine leafroll disease (GLD) is an example of such a system, where distinct virus species in the family Closteroviridae cause similar disease symptoms [1]. GLD is caused by a complex of about ten virus species (Grapevine leafroll-associated virus 1, 2, and so on) in the family Closteroviridae. Within-species diversity, as shown for GLRaV-2, can lead to different combinations of symptoms being expressed [12]. This is of practical relevance as management of diseases with different etiology may vary substantially. There is great insight to be gained from identifying the major causal agents of GLD in specific regions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
