Young Vine Decline is studied closely in NSW

Young Vine Decline is studied closely in NSW

In 2006, NSW DPI extension officer Leo Quirk and I sent survey questionnaires to more than 500 winegrape growers. The replies showed that more than 65 per cent had recently experienced this sort of Young Vine Decline. Many invited us to inspect their diseased young vines. Suddenly we had our first real view of the extent of the problem; growers were losing a lot of money. Some comments from these growers:
'Of 6000 grafted grapevine rootlings planted, 1000 were diseased.'
'Too many growers are losing money constantly - the vines are extremely slow growing in the early years, and then they often have to be removed and replaced after a few years.'
'The next season (after planting) we had about 15-20% not grow or were severely stunted. There seems to have been a lot of this sort of problem about.'
'My 30 acre patch (planted 2002) of Chardonnay lost 500 vines in 2004 and about another 100 vines in 2005.'
'The first time I saw Young Vine Decline was in 1992 when it appeared on young Chardonnay rootstock. We lost close to a third in the two next years.'
We received funding from the Grape and Wine Research and Development Corporation to try to find the cause of this disease which we named Young Vine Decline (YVD) because it was similar to YVD found in many viticultural regions worldwide. As YVD can be caused by the Petri disease (black goo) fungi, we made a thorough attempt to isolate the fungi responsible: Phaeomoniella and Phaeoacremonium. However, in our case the Petri disease fungi were isolated from less than 20% of our diseased vines, casting doubt on their role in YVD in the Riverina. From the vine position infected, we reasoned that in the Riverina the Petri disease fungi sometimes originated in the nursery propagation process, but other times were infecting the scions (above the graft union) of vines already infected with other pathogens.
The roots of YVD vines in the Riverina were extremely stunted, so we decided to further our investigation by trying to isolate pathogens from the roots and rootstock wood of the diseased vines. We found a very strong association between our YVD and quite different pathogenic fungi (from 89-100% of all diseased vines were infected).
Further trials showed the disease was actually caused in most cases by two
fungal pathogens present in planting stock. One of the pathogens, Botryosphaeria (Bot), originated in infected mothervine canes in rootstock source blocks. The other, Ilyonectria (formerly Cylindrocarpon), was introduced from the nursery environment, including field nursery soil.

Results of our study
Generally, the scion (i.e. above the graft union) was clean (free of pathogens) but pathogenic fungi were found in the oldest (i.e. the innermost) xylem of the rootstocks of the diseased plants (Figures 1b, 1c) indicating that the infection occurred before, or very early in, the propagation process.
Bot was isolated from the oldest xylem of rootstock stems and roots, sometimes extending up to the graft union. Ilyonectria was isolated from the roots, and from the oldest xylem of the rootstock stem, close to the roots.
Both Bot and Ilyonectria can also infect mature or young vines on their own. The fact that the YVD Bot and Ilyonectria were isolated from the oldest xylem, and that the infection was found throughout the rootstock stems, indicated that these fungi must have been acquired before they were planted in the affected vineyards.
Many Riverina growers said the diseased vines looked 'quite healthy' to them before planting. This means the vines probably also looked perfectly acceptable to nursery staff before they were freighted out to the vineyards. Unless the stems are cut open and examined, the symptoms do not generally show until the vines are planted in the vineyard.
Composts have been shown to cause grapevines to recover from Petri disease over time1. Unfortunately we found that, although composts or fungicidal soil drenches caused a short-term improvement in root structure, the diseased grapevines were not cured and yields were not improved. This is most likely because the Ilyonectria destroys the root system and prevents the plant from absorbing water and nutrients, increasing the damage caused by the Bot fungal hyphae and toxins.

Where do the Bot/Ilyonectria YVD fungi originate?
Our research has shown that Bot first infected the rootstock mothervines and thus the canes harvested from them. Infected cuttings probably then contaminated others during hydration and/or storage in moist conditions in the nursery. Correctly applied hot water treatment (HWT) of the cuttings (50°C for 30 minutes) kills the fungus and reduces this risk but many Riverina growers were not asking for their cuttings to be hot water treated.
We found that Ilyonectria then enterered the basal callus in the cuttings when they were rooted in contaminated nursery soil. Ilyonectria might also be present in some rootstock cuttings.

Conclusion
There is no cure for Bot/Ilyonectria induced YVD. YVD-affected vineyards cannot recover with management practices reducing stress (e.g. composts or biochar), or by application of fungicide soil drenches.
The best approach is to avoid buying infected propagated vines. Ask your supplying nursery to use HWT on the canes immediately before propagation.
Helen Waite (NWGIC grapevine nursery expert) advises that nurseries should allow the cuttings to come to ambient temperature before moving them from cold storage to HWT tanks. This may take 24 hours or more. If cold cuttings are hot water treated the large temperature differential may cause fatal shock. It is also essential that the cutting bags/bins, while returning to ambient temperature, are ventilated to allow oxygen to reach the cuttings but without drying out.
Nursery field site soil must be free of Ilyonectria, so the nursery should use some method of fumigation. NWGIC nematode expert Dr Loothfar Rahman has published methods for biofumigation using brassicas (e.g. mustard). Brassica biofumigation reduces not only soil parasitic nematodes, but a New Zealand study by Carolyn Bleach in 2010 showed that it also decreases soil Ilyonectria.
When growers purchase new grapevine planting material, it is important, before planting, to check the health of the vines carefully by cutting the stems below the graft, through the graft union and above the graft. Dark spots or wedges in the stem mean that the vine is probably diseased (Figures 1c, 1d, 1e).
Replanting problems: Ilyonectria propagules are likely to remain in the planting holes for years, causing disease in the new replants. Brassica biofumigation may be the answer, but Australian trials are required before we can properly know whether Brassicas can kill soil-borne Ilyonectria in Australian conditions.

Acknowledgements
We are grateful for the support from the many Riverina NSW growers who answered the questionnaire, invited us onto their vineyards, supplied samples of diseased roots or rootstock stems and allowed their vineyards to be included in our field trial work.
The NWGIC Wine Growing Futures project, titled Young Vine Decline, was jointly funded by the GWRDC, NSW, the Department of Primary Industries and Charles Sturt University. We are also grateful to the Wine Grapes Marketing Board, in Griffith (including Jason Capello and Kristy Bartrop) for their support over the years. We also want to thank Helen Waite, professor Jim Hardie, Dr Loothfar Rahman and Suzy Rogiers, from the NWGIC.
Harry Creasy (NSW DPI horticulturist, now retired) was the first to discover the Young Vine Decline problem in the Riverina and his work started this investigation.
Lynne Appleby and Robert Lamont provided technical assistance. Leo Quirk then continued Harry's work by interviewing affected grapegrowers and surveying healthy and diseased vines from over 20 affected Riverina vineyards. NWGIC chemist Dr. Andrew Clark, with assistance from Lindsay Greer, discovered that the Ilyonectria isolated from the Riverina produced a phytotoxin Brefeldin A that is known to increase virulence. Dr. Andrew Hall, with assistance from Mark Wilson, was able to do remote sensing 'fly-overs' and established that the position of individual low vigour plants within typical Riverina vineyards affected by Young Vine Decline could be predicted using remote sensing.
Visit www.gwrdc.com.au to read the full report.

Reference
1. Edwards J, Pascoe I, Salib S, Laukart N, Richardson F, 2007. Chapter 7, 'Control and management of Petri disease in the vineyard' in 'Managing Grapevine Trunk Diseases (Petri Disease, Esca, and Others) That Threaten The Sustainability of Australian Viticulture'; Final Report to GWRDC. Project no. CRCV 2.2.1.

Other feature articles

AWRI


Flavourtech


Beverage Info Systems


New Holland


Rowe Scientific


Braud


Canberra Int Riesling Challenge


WEA


Fischer


IMCD


Groguard


WID 2017