The aim of these projects were to study the transmission efficiency of different variants of GLRaV-3 as well as their transmission dynamics in mixed variant infections. In South Africa leafroll is caused by a virus called grapevine leafroll associated virus -3 (abbreviated GLRaV-3), which belongs to the family Closteroviridae. The variants of GLRaV-3 are often found in mixed, multiple infections in vines in South Africa. A number of genetic variants of GLRaV-3 are found in South Africa, but the differences in their biological properties (severity of symptoms, efficiency of transmission, yield losses) are unknown.
Project layout:
Project 1:
- The first project studied the transmission efficiency of four individual variants by mealybug from one plant to another when they were present individually and when present in combination with GVA.
Project 2:
- The second project investigated the transmission efficiency of individual variants when the source plant was infected with different combinations of the variants (mixed variant GLRaV-3 infections). Some combinations were also co-inoculated with other vitiviruses GVA, GVE and GRSPaV, to determine transmission dynamics in the presence of other vitiviruses.
Results:
Project 1:
- Even though variant II and VI are most prevalent in South Africa, the research showed that all variants are transmitted equally well under controlled conditions, whether occurring as single infections or in combination with GVA. This suggests that factors other than the mealybug vector play a role in the prevalence of groups II and VI.
Project 2:
- The study demonstrated that where combinations of variants are present in source plants, GLRaV-3 variants from groups I and II established better in recipient plants during transmission. Transmission occured either as single transmissions, or in combination with each other. This suggests that competition between variants exist, either in the mealybug vector, or in the recipient plant after transmission.
- GVA was transmitted in higher frequencies than GVE.
- The interaction between GVA and the group II variant needs to be investigated in more detail.
Significance of the study:
The results from these studies created knowledge on virus-vector interactions and transmission dynamics of GLRaV-3 variants. This knowledge will impact future management strategies of leafroll disease spread.
Link to final reports:
http://www.sawislibrary.co.za/dbtextimages/JoosteAEC2.pdf
http://www.sawislibrary.co.za/dbtextimages/JoosteAEC3.pdf
Photo: Prof. Goussard
