|
A Technical Guide for Wine Producers
|
|
RECENT ARTICLES | WYNBOER HOME
VINE IMPROVEMENT AND AVAILABILITY OF PLANT MATERIAL
1. HISTORICAL PERSPECTIVE
Initially KWV's Plant Improvement Programme operated as a service function to its 5 000 wine farmer members in collaboration with the Department of Agriculture, and until 1986 it was the only official propagation organisation in the Government certification scheme for wine grape vines. In 1986 KWV initiated the foundation of the Vine Improvement Association (VIA), involving all the role players in the industry, and it has since been the official propagation organisation. In 1993 the nurseries and producers became involved as full-fledged members and nowadays all aspects of plant improvement, propagation and certification are co-ordinated by the VIA. Three departmental members serve in the Executive Board in an advisory capacity.
2. CURRENT SITUATION
2.1 General: At present vine improvement in South Africa is strategically planned and co-ordinated by the VIA, involving all the role players. This is done by means of the "SA Certification Scheme for Wine Grapes" which was promulgated in terms of the Plant Improvement Act. The VIA manages the scheme with delegated authority and is audited by the Registrar of Plant Improvement.
The original government certification scheme was rewritten by the VIA to make provision for shortcomings in basic research and technology. Furthermore it makes provision for the continuous upgrading of minimum requirements for certified material, in keeping with progress in research and technology development for the elimination of causative entities and virus detection techniques. The original "Super Grade" certification scheme of the Government failed because it was too idealistic, setting unrealistic certification requirements which could not be met with existing technology. As a result, the current certification scheme makes provision for the certification of the "best available" plant material. As technology improves, better clones and sources are phased in and old clones and sources are phased out.
The South African Plant Improvement and Propagation Programme, as co-ordinated by the VIA, is generally considered to be among the best in the world. Although participation is voluntary, in some years more than 90% of commercial grafting material has been certified.
2.2 Quality of plant material
2.2.1 Genetic: South Africa currently has some of the best scion and root stock plant material gene pools in the world. Clone selection, both viticultural and oenological, using local as well as imported clones, is conducted up to the wine stage to identify the best clones for local conditions. A wide range of gene pools, which are very important building blocks for wine, exists within all the important cultivars. At present clone selection only takes place when clones are known to be free of identified harmful viruses, in order to determine true genetic characteristics without the interference of harmful virus combinations.
2.2.2 Phytosanitary: South Africa has core sources of a wide range of scion and root stock clones within the most important cultivars, which, using existing technology, test free of known harmful viruses. The number of clones, including international clones, which have been cleansed of harmful viruses using the best available technology, exceeds that of any other wine country in the world. Most of the clones imported from Europe were infected with the stem pitting virus and have been cleansed locally. Nepo viruses (fanleaf) are no longer a problem in South African plant material and all certified material released to the trade is free of fanleaf.
2.2.3 Physical standards: Although the physical standards prescribed by the certification scheme for plant material apprehends visible impairments, it is difficult to predict the ability of the material to callus, root and grow in the vineyard. A research project addressing this problem is currently being funded at ARC Nietvoorbij. The ideal would be to have a measuring instrument for control purposes. It may be stated categorically that the physical quality of certified grafting material and grafted vines is much better today than the uncontrolled material of 25 years ago. Take success rate has improved dramatically and established vineyards and the vines testify to the progress that has been made.
2.2.4 Production Vineyards: South African Production Vineyards, of which the unit yield ranked with the lowest in the world 25 years ago, is currently one of the highest, despite switching to more noble cultivars. This went hand in hand with a corresponding increase in wine quality. Wine makers prefer fully ripe grapes from healthy vineyards to make the best quality wines from noble cultivars.
3. PROBLEMS WITH THE SUPPLY OF PLANT MATERIAL
3.1 Availability
3.1.1 Root stocks: The availability of root stock grafting material during years of normal replacement and growth is not a problem, thanks to co-ordination within the VIA. This is demonstrated by available statistics. The problem arises at the time of sudden upsurges, as with the general election in 1994, after which world markets opened up.
In 1990 about 6,5 million of the 15,5 million grafted vines were not sold. Only 24,8 million vines were grafted in 1990, causing very large surpluses of certified root stock cuttings. After 1994 the demand for grafted vines increased dramatically, causing huge shortages. As it takes three to four years before new sources of root stock cuttings come into production, the 1998 supply of approximately 53 million cuttings testifies to good pro-active measures. Established sources can potentially supply approximately 60 million cuttings in 2001, already hinting at potential surpluses.
This problem is not unique to South Africa. In the mid-1990's Europe experienced enormous shortages of root stock cuttings, after big surpluses in 1988/89. In the past, KWV Plant Improvement stabilised the supply of root stock material to the nurseries and industry to a large extent. This function now falls away and in future nurseries themselves will have to make provision for their needs. Hopefully the wine industry Vision 2020 will project guidelines for the industry requirements.
The current cultivar spectrum of root stocks is sufficient for the different soil types in the industry. Resistance against viruses and fungal and bacterial diseases by means of genetic manipulation will have tremendous advantages.
3.1.2 Scions: The availability of certified scions should not pose a problem within the present co-ordinating function of the VIA. The current shortage of certified scions of noble red cultivars may be ascribed to the sudden switch in industry requirements, from a ratio of approximately 80 white: 20 red to approximately 20 white: 80 red cultivars. This potential turnaround was not foreseen by the VIA, notwithstanding the input of all role players. A further contributing factor has been the rapid reinfection of noble red cultivars with leafroll. Here too nurseries will have to make provision themselves for future sources of supply. However, the VIA will still have to project trends if the industry wants to ensure a continuous supply of the right quantities of grafted vines. In this regard also the wine industry Vision 2020 will be able to make a valuable contribution.
3.2 Leafroll reinfection
The single biggest hurdle for plant improvement in South Africa is the reinfection of "clean" sources and newly established commercial vineyards with leafroll, and to a lesser extent Shiraz disease in certain cultivars.
The well-known cause of reinfection is the widespread occurrence of the mealy bug vector in South African vines, while other unknown vectors are also suspected. The elimination of reinfection requires 100% control of mealy bug in the sources and vineyards, which is very hard to achieve. The most effective control of mealy bug is biological control, for which a limited presence of mealy bug is required, which in turn enables reinfection.
Effective ant control, a further prerequisite for control of mealy bug, occurs through chemical substances, as does the alternative control of mealy bug. These chemical substances are unacceptable within the integrated production programme (IPP) and total long term control is hard to achieve.
Although claims are sometimes made that virus elimination and detection technology may have failed and that the source material is not always clean, this is negated by the fact that clones in the insect-free nucleus blocks are still "clean" after several years.
Various research projects which address the above-mentioned problem have been financed by Winetech for approximately 5 years, but progress is disappointing. The most obvious solution lies in genetic transformation, whereby the leafroll resistant gene will be placed in all the most important commercial clones of the most sensitive cultivars. The Winetech project in this regard is already making good progress, but it is a medium/long term solution and will not be commercialised in the next five years at least (some overseas researchers reckon ten years).
Recommendation. It is recommended that a multi-disciplinary task team, with funding from Winetech and a full time leader, be appointed to propose a solution or at the very least submit recommendations for minimising the problem. The task team should include at least one each of the following disciplines, namely, a virologist, an entomologist with experience of virus vectors and somebody with a solid knowledge of mealy bug and ant control in vineyards. Recently established mother blocks of "clean" material may be used as investigative and experimental premises and technical plant improvement personnel may provide input about distribution.
3.3 Vines dying after planting
Although occasional complaints about certified grafted vines not growing after establishment in the vineyard are still being received from the industry, the situation has improved drastically compared to the era before the VIA and the SA Certification Scheme. Vineyards established from certified clone material have a much more even appearance and ripening is much more even, resulting in fruitier wines.
The most common reason why certified vines die after being planted is desiccation -either before or after planting. Since desiccation may occur after certification, the certification label cannot provide such a guarantee. Vines with little reserves as a result of disease or malnutrition in the nursery also dry out much more quickly. In the Orange River area a further problem occurs after one to two years in the vineyard, with vigorous vines not budding after the winter and dying. Low winter temperatures combined with vigorous growth late in the season (autumn) probably play a big role in this case. The above problems are currently being addressed by registered Winetech research projects.
Minimum physical standards such as graft union requirements, root development and growth of shoots are, however, guaranteed by the certification label, as well as cultivar and clone authenticity.
4. CONCLUSION
In South Africa, perhaps more so than in any other country, plant improvement has contributed to increased producer and nursery income and improved wine quality. Compared to old wine countries such as France and Germany, where selection has been taking place for more than 100 years, this has occurred over a relatively short period by making use of all internationally available technology.
Plant improvement is an ongoing process with continuous phasing in of improved technology. Biotechnology offers immense possibilities in the form of transformed clones for specific wine objectives.
|
|
Wynboer is incorporated in WineLand, magazine of the SA wine producers.
Visit our sister sites:
|
In the sixties KWV realised that South African wines could only be improved by improving the condition of our vineyards. The driving force behind this conviction was the late Mr Beyers Henning, production manager. The average yield was amongst the lowest in the world with the accompanying low quality wines. The main reason for the poor condition was the effect of harmful viruses and virus combinations in the plant material, together with mass producing cultivars. On the whole grafting material was collected at random in vineyards where disease was already present. A survey conducted in 1970 indicated that 99,7% of the vineyards were infected with some or other harmful virus or virus combinations - mainly Nepo (Fanleaf group), Clostero (Leafroll) and Viti viruses (Stem pitting, corky bark, Shiraz disease). Success rates in nurseries were as low as 15 - 20% due to the effect of combinations of these viruses in the grafting material (low affinity). Young established vineyards were very uneven with lots of vines dying in the first year and gradual deterioration in later years.
| UP |
COPYRIGHT (C) 2000 WineLand |