Grapevine leafroll disease causes poor color development in red grape varieties and non-uniform maturation of fruits in Vitis vinifera. It also has been reported to cause delay in fruit maturation from 3 weeks to a month and crop losses of as much as 20-40%. This project was planned to study the effects of GLRaV types -1 and -2 (2 isolates each), -3 (3 isolates), -4, -5, -7 and -9 (one isolate each) and a combination of two of types -1, -2 and -3 each and with -5 and -7 on Cabernet Franc grafted on 9 different rootstocks. Rootstocks used are AXR #1, Mgt 101-14, 110R, 3309C, 5BB, 420A, Freedom, St. George 15 and St. George 18.
The data collected from the experiment in 2012 showed that the mild leaf symptoms started in the month of July for GLRaVs-1, -2 and -3 and become very severe when recorded in November. Plants inoculated with GLRaVs-4, -5,-7 and 9 were asymptomatic in July and showed mild leaf symptoms in November except for GLRaV-7 that stayed asymptomatic. Leaf symptoms differences were not observed between different isolates of the same virus except for the isolate LR132 (GLRaV-1+GVA) which had a lethal reaction on Cabernet Franc plants propagated on 420A, Freedom, 3309C and 101-14 rootstocks.
In treatments with two different virus isolates, more severe symptoms were noticeable even in cases that one of the isolates in the treatment belonged to the group with mild symptoms (GLRaV-4, -5 and -9). When the effects of viruses on different rootstocks were compared, no significant differences were observed except for Cabernet Franc plants propagated on AXR-1 which were showing slightly milder symptoms. Both isolates of GLRaV-2 showed solid red leaf symptoms on plants propagated on 3309C, Freedom, 101-14, 5BB and 110R and in many cases the plants were observed to be weaker and many having short internode and were stunted. Both of these GLRaV-2 isolates killed the plants propagated on 5BB rootstock.