| The controversy about the extent of two viruses reported by NCR or even the very existence of the virus continues in Maharashtra, where the winegrape growers feel that the report has been sensationalist and might damage the long term interest of farmers.
The growers are upset and are planning to have a meeting with NCR this week to understand how it has declared the existence of the viruses when it might not be fully capable in terms of expertise for wine grapes and equipment to determine whether the virus existed.
According to the growers, including Rajeev Samant of Sula Vineyards, the incident of virus is not considered dangerous if up to 10% plants carry the infection. The extent to which the vines may be exposed is certainly less than this figure, they claim. Countries like Italy, Australia, Spain and South Africa and even California are frequently infested with similar problem.
Prahlad Khadangle, Chairman of Sankalp Winery, Nashik was categorical while talking to delWine and denied that there is any rampant virus problem in Nashik or even Maharashtra. Agreeing with the sentiment echoed last week by Samant, he says, 'I have been a farmer growing grapes since 1998. I can say it with confidence that the virus does not exist. We have noticed a bit of curling of leaves on a few vines, which could be due to leafroll or also due to lack of potash. Some vested interests seem to be amplifying the problem.'
He also feels a section of growers are trying to malign Chougules who have been able to run the recently started nursery with French co-operation, quite successfully. As an example he said, 'it costs Rs.65 ($1.60) each for an imported plant but only Rs. 35 to buy one from them. I have been using there cuttings and I have had no problems.'
Spread of Virus through imported plants
Since there are not enough plants to go around, they are still being imported from France, Italy and Australia, says Prahlad. It is not as if the imports are control-free. Import of agricultural products to India is regulated through the Plant Quarantine Order, 2003.
The regulations may be in place but 'There are instances when infected plants easily escape the quarantine', says State Agriculture Commissioner Krishna Lavekar. 'We need more stringent quarantine methods so that no virus is imported,' he adds.
"The existing system lacks curbs on entry of infected plant material. There must be thorough observation of imported plant material which shows no symptoms of infection in early stages but could turn into a big problem after a few years," says Dr S.D. Sawant, plant pathologist, NRC
What is Leafroll Virus
For the technically inclined, leafroll is one of the most important viral diseases in grapevines and occurs wherever grapevines are grown. At least nine different grapevine leafroll associated viruses (GLRaVs) have been reported.
Typical leaf symptoms include reddening of the leaves between major veins in red varieties, and yellowing of the leaves between major veins in white varieties. Leaves become thick, brittle, and roll downwards. GLRaV3 is transmitted by a mealy bug. The causes for the other GLRaVs are still unknown.
All of the leafroll viruses are spread by grafting and have been widely distributed and accumulated in their long-lived host over time by human activities. The causal agent of the rugose wood disease complex, which includes corky bark, has been attributed to members of the genus 'Vitivirus' such as Grapevine virus A (GVA) and Grapevine virus B(GVB). They are spread by mechanical means, infected planting material and grafting. GVB is transmitted in a semi-persistent manner by different species of mealy bugs and is widely distributed.
Impact of Virus on Wine
Viral diseases can have a serious impact on vine health, yield, and quality of the fruit. Symptoms are not always severe or obvious, but even a small decrease in yield will add up over time causing significant economic losses. Decreased yields of 5 to 10 percent are not uncommon, and losses can be much higher, up to 70%.
The virus reduces yield by inhibiting cluster formation and development. Infected vines have an increased sensitivity to environmental stress also.
Viruses may also influence wine quality by causing delays and reduction of 25-50% in sugar accumulation, poor acid and colour development. The difficulty of detecting virus infection can lead to rapid dissemination of virus-infected material through propagation. When infected cuttings are used for propagation, whole vineyards can become infected.
Leafroll and Rugose Wood virus reported
Although the report from NRC Pune names only two diseases- leafroll and rugose wood, each of these may be associated with several viruses. The total number of viruses infecting these grapevines may therefore be higher. Virus sources may be both local and introduced plant material, and stopping all new plant imports may not solve the problem either. It is important to know that the Virus-infected plants cannot be cured, only removed and replaced by certified material. Both the rootstocks and grafting material need to be tested when establishing new plantings.
Similar virus problem in California
Avatar Singh Sandhu, and NRI owner of Mushal Winery in Sonoma is sympathetic to the problem as he and other farmers in California occasionally have to suffer it too. He informs delWine, 'We have leaf roll virus throughout California. We avoid the problem by using only certified plant materials when buying or grafting vines. It is typically spread by humans through risky propagation practices. It is possible that it is also spread by grape mealy bug as well though this is a more current belief only.'
How to avoid the Virus
'We are controlling grape mealy bug entry into Northern California by screening all incoming plants including household floral plants and vines. The mealy bug if it is prevalent in Maharashtra due to the fruit orchards can be devastating for grape vines. I am sure the Maharashtra State Department of Horticulture knows how to deal with this problem using pesticides,' says Sandhu
Having grown up in Punjab, Sandhu has a piece of relevant advice, ' I know that in my father's house as a child I used to see our gardener putting a mixture of lime and dissolved Copper Sulphate on the trunks of our mango trees. It was inexpensive and effective.'
Oak Root fungus in California and its relevance
Duff Bevel, member of the Sonoma Wine Grape Commission has offered some technical information and advice that may be helpful to the vineyard owners or students of viticulture.
'In California there is an epidemic of 'Oak Root Fungus'. It kills an otherwise healthy and large Oak Tree in a matter of a year or two. It transmigrates and affects the vines in the vicinity of the infected Oak Tree. There is no effective cure, except to replace and burn the infected vines. This problem should also be examined in Maharashtra where the fungus may have been present in the soil prior to planting the Vines. If possible, new Vineyards should be treated with 'Methyl Bromide' which is injected in the soil prior to planting.'
Conclusion
The vine world in Maharashtra is going through the virus problem but as mentioned by Rajeev Samant during his chat with delWine last week, there is no cause of panic. The problem is within the solving capability of the vineyard owners. In order to avoid a major economic crisis they need to be cool, united and on the same side of the fence.
Resource:
International Society for Infectious Diseases (ISID) has done a lot of work in this area and a lot of useful information is available- there as also on its PromedMail programme.
http://winegrapes.tamu.edu/grow/diseases/leafroll.shtml
http://www.agf.gov.bc.ca/cropprot/grapeipm/virus.htm
http://www.isid.org
http://www.promedmail.org |
