GLD and Its Effects
Grapevine leafroll disease (GLD) is one of the most widespread and economically damaging viral diseases in grapevines worldwide. GLD causes reddening of the interveinal areas while the primary and secondary veins remain green. The major effect of leafroll disease is the production of small grape clusters with uneven ripeness. Grapevines may have reduced growth, resulting in smaller canopies as well as lower qualities such as reduced sugar levels, aromas, color, and excessive acidity, which damage the market appeal and usability of the grapes. Symptoms of GLD can vary greatly with the season, grape cultivar, and climatic conditions.
Little is known about the economic effects of GLD, with a few notable examples. The estimated economic impact of GLD on Vitis vinifera cv. Cabernet Franc in vineyards in the Finger Lakes region of New York ranges from approximately $25,000 to $40,000 per hectare in the absence of any control measure.
No sources of GLD resistance have yet to be found in V. vinifera cultivars and clones. Once the virus has infected a vineyard, it is impossible to eliminate it without destroying the vines. Therefore, uprooting vines and quarantine are currently the only treatments for this disease.
Severe GLD symptoms
Proof of Concept for RNA Based Treatment
Field trial was conducted in a vineyard located in Karmei Yosef, Israel, using Cabernet Sauvignon cultivar vines, over a period of three years with repeated treatments. The objective was to determine the efficacy of the RNAway based treatment against GLD for the following categories:
- Disease assessment
- Virus titer
- Berry parameters
Trial design
Included 3 treatment groups: healthy vines, infected vines untreated, infected vines treated with the RNAway based treatment.
The RNAway based treatment was applied to the vines via foliar spray from bud burst until ripening.
Disease Assessment
Six shoots from each vine were labeled and tracked from the beginning of the trial. Over the course of the season, disease incidence and severity were assessed.
Data shows that disease symptoms were significantly decreased with the RNAway based treatments, as seen in the red and green lines in the graphs below.
GLD incidence assessment throughout the field trial
GLD severity assessment throughout the field trial
Berry Parameters
At the end of the trial, the first primary cluster was sampled from each shoot from each vine. Berries were sent to a certified laboratory and tested for soluble sugar (Brix) and other berry quality parameters.
Data shows that the RNAway based treatment significantly recovered Brix values when sprayed on infected vines. This correlates with berry cluster images taken at harvest emphasizing the recovery of berry yield and ripening.
Berry clusters images after field trial (harvest)
Quantification of soluble sugar in berries after harvest
Virus Titer
From each of the six shoots per vine, the fourth leaf was sampled at the end of the trial for virus titer assessment and was analyzed using real-time PCR.
Data shows that the RNAway based treatment succeeded in significantly downregulating viral load in sprayed infected vines. Also, the RNAway based treatment exhibited systemic effect when silencing virus titer in distant tissues that were not directly sprayed.
GLRaV-3 relative gene expression
Conclusion
In conclusion, key parameters were not significantly different between healthy vines compared to vines treated with the RNAway based treatment, while those changed significantly between untreated infected vines and treated ones.
Therefore, RNAway based treatment is effective against GLD.
