Kunihisa Morinaga*
*Persimmon and Grape Research Center, National Institute of Fruit Science, MAFF, Akitsu, Hiroshima 729-2494, Japan.1. INTRODUCTION
Several species of the genus Vitis, such as Vitis coignetiae Pulliat., V. flexuosa Thumb., and V. amurensis Rupr., are native to Japan. However, they have not been brought into cultivation or for breeding. The first grape culture in Japan dates back to the 12th century, when a wild grapevine bearing good fruit bunches was found in Yamanashi. The vine was apparently not native to the land, suggesting that its ancestor might have been imported from China in the 8th century. The progenies from the vine adapted to the environment of that district, and the cultivar ‘Koshu’ was thus released. In the 17th century, ‘Koshu’ grapes became famous for their excellent fruit quality. In the late 19th century, the Government actively imported numerous species including V.vinifera, V.labrusca, and V.labruscana from the USA and European countries. However, most vinifera grapes could not be cultivated successfully because of the spread of diseases. Only a few vinifera cultivars, such as ‘Muscat of Alexandria,’ could grow normally with the aid of glasshouses. The vines of both V.labrusca and V.labruscana, on the other hand, grew successfully. ‘Catawba,’ ‘Campbell Early,’ and ‘Delaware’ were planted in Yamanashi, Osaka, and Okayama prefectures in the early 20th century.
Grape growers tried to breed new good quality table grapes suitable for the humid conditions of Japan. Some cultivars, such as ‘Kyoho,’ ‘Muscat Baily A,’ ‘Neo Muscat,’ and ‘Hiro Hamburg,’ were identified from the crosses between V. vinifera and V. labruscana or between vinifera grapes in the middle 20th century. These cultivars, however, could not be cultivated successfully because of poor berry set and susceptibility to fungal attack in those days.
The cultivation of grapes grew rapidly from 1960 to 1980. Success in the production of seedless ‘Delaware’ grapes by GA treatment further accelerated the spread of this cultivar. The cultivar ‘Kyoho,’ famous for its large sized berries and excellent taste, was also planted throughout the country except in Hokkaido, the northernmost island. Another contribution in the development of grape growing was the application of plastic films, which greatly decreased the spread of diseases and increased both yield level and fruit quality. The practice of forcing culture by heating the vines in plastic houses also spread. Recently, propagation of virus-free vines has been developed using the technology of in-vitro cultures of heat-treated stem apices. Vine growth and fruit quality have also been significantly improved. This has resulted in the spread of virus-free vines in most newly established vineyards that are suitable for replanting. The main producing areas have been established in the north, central, and western districts of the country.
Viticulture in Japan started from adoption of the variety ‘Koshu’ (Vitis vinifera var. orientalis), which was discovered in Yamanashi in 1186. Thereafter, European and American grape cultivars were introduced in the 1800’s. Most V. vinifera grapes from Europe could not grow well because of serious damage by Phylloxera and many other diseases. On the other hand, American cultivars derived from V. labrusca were suited to the Japanese environmental conditions. ‘Delaware,’ ‘Campbell Early,’ ‘Niagara,’ and ‘Concord’ became popular at the beginning of the 20th century. Thereafter, the popularity of ‘Kyoho’ increased rapidly in the 1970’s.
It is important to develop new grape cultivars that are well suited to the Japanese environmental conditions and consumers’ preferences. Grape-breeding programmes in Japan that originated in the 1920’s aimed at these objectives. More than 200 grape cultivars have been developed so far. Thus, conventional techniques by cross-hybridization have contributed to the development of the grape industry. However, when using this approach, not only desirable but also unfavourable characteristics are inherited. Recent advances in biotechnology offer many strategies, such as gene transformation and molecular markers for breeding, and may help overcome the limitations of conventional techniques.
2. PRESENT STATUS OF GRAPE CULTIVATION IN JAPAN
Grape production has been undertaken in all four main islands in Japan from north to south. The major producing regions are Yamagata, Yamanashi, and Nagano prefectures in the northern and central parts, and Okayama and Fukuoka prefectures in the southern part of Japan (Figures 1 and 2). In 1997, the total grape production was 250,900 metric tonnes (Figure 3), and the vineyard area was 22,800 hectares. (Figure 4). Most vineyards in Japan produce table grapes. In 1997, table grapes made up 87.4 percent of the total production, while 11 percent and 1.4 percent went to the production of wine and juice, respectively.
Figure 1. Major Areas of Grape Production in Japan (table grapes, metric tonnes, 1997)
Figure 2. Major Areas of Grape Production for Processing (metric tonnes, 1997)
Figure 3. Total Production of Grapes
Figure 4. Total Area Under Cultivation
Table 1. Grape Production and the Proportion of Table Grapes and Grapes for Processing (1997)
|
Product |
Production (tonnes) |
Proportion of total production (%) |
|
Table Grape |
219,300 |
87.4 |
|
Wine |
27,700 |
11.0 |
|
Juice |
3,500 |
1.4 |
|
Canned Fruit |
400 |
0.1 |
|
Total Production |
250,900 |
100 |
Table 2. Main Cultivars Grown in Japan (table grapes, 1997)
|
Cultivars |
Area (ha) |
Proportion (%) |
|
Kyoho |
6,531 |
33.0 |
|
Delaware |
4,878 |
25.0 |
|
Campbell Early |
1,500 |
7.6 |
|
Pione |
1,400 |
7.5 |
|
Muscat Baily A |
864 |
4.4 |
|
Niagara |
492 |
2.5 |
|
Kosyu |
470 |
2.4 |
|
New Baily A |
382 |
1.9 |
|
Cultivars |
Area (ha) |
Proportion (%) |
|
Yamabudo (V. coignetiae) |
124.2 |
19.8 |
|
Muller Thurgau |
102.7 |
16.4 |
|
Chardonnay |
96.3 |
15.3 |
|
Merlot |
88.6 |
14.1 |
|
Cabernet Sauvignon |
69.9 |
11.1 |
|
Seibel |
69.7 |
11.1 |
Table 4. Description of Table Grape Cultivars Bred in Japan
|
Cultivar (Polyploidy) |
Parentage |
Fruit Description |
|
Aki Queen (4x) |
Kyoho x Kyoho |
End Aug., very large, bright red, excellent quality |
|
Fujiminori (4x) |
Ikawa 682 x Pione |
End Aug., very large, dark purple-red, good quality |
|
Honey Seedless (3x) |
Kyoho x Concord Seedless |
Mid-Aug., medium berry (GA), greenish yellow,
seedless |
|
Kaiji (2x) |
Flame Tokay x Neo Muscat |
Early Oct., large, bright red, excellent quality |
|
King Dela (3x) |
Red Pearl x Muscat of Alexandria |
Early Aug, small (GA), red-brown, seedless, good
quality |
|
Koshu (2x) |
Unknown |
Early Oct., medium, red-purple, medium quality |
|
Kyoho (4x) |
Ishihara Wase x Centennial |
End Aug., very large, violet-black, excellent
quality |
|
Mirei (3x) |
Red Queen x Koshu Sanjaku |
Mid-Aug., medium (GA), yellow-green, good quality |
|
Muscat Bailey A (2x) |
Bailey x Muscat Hamburg |
Mid-Sept., very large, bluish black, medium quality |
|
Neo Muscat (2x) |
Muscat of Alex. x Koshu Sanjaku |
Early Sept., large, greenish yellow, muscat flavour |
|
North Red (2x) |
Seneca x Campbell Early |
Mid-Aug., medium, red-brown, sweet, foxy |
|
Pione (4x) |
Kyoto x Cannon Hall Muscat |
Early Sept., very large, violet-black, excellent
quality |
|
Rosario Bianco (2x) |
Rosaki x Muscat of Alexandria |
Mid-Sept., very large, greenish yellow, excellent
quality |
|
Sekirei (2x) |
Early sport of Kaiji |
Mid-Sept., large, bright red, excellent quality |
|
Suihou (4x) |
Pione x Centennial |
Early Sept., very large, green-yellow, excellent
quality |
|
SummerBlack (3x) |
Kyoto x Thompson Seedless |
Early Aug., large (GA), purple-black, seedless, good
quality |
Private nurseries produce most of the planting material such as rootstocks from cuttings, and then scions of commercial cultivars are grafted. Saddle grafting has produced over 90 percent of grape planting materials. Another popular grafting method is cleft grafting.
In the early 1920’s, ‘3309,’ ‘3306,’ and ‘101-14’ rootstocks were introduced to Japan. After that, the ‘420A’ and ‘Teleki’ strains were also introduced. Growers have chosen ‘Teleki 8B,’ ‘5BB,’ and ‘5C’ because of their excellent characteristics, including high berry quality, early ripening, and wide soil adaptability. These are the reasons why they are still the major rootstock varieties in Japan.
4. ESTABLISHMENT OF VINEYARDS
Land Preparation
The land selected for vineyards should have a gradient of less than 5 degrees, underground watertable below 1 m, long hours of solar radiation, average annual rainfall of 1,000 mm, and, in particular, a low amount of rainfall during the harvest season. Long drainage pipes with small holes should be buried to drain underground water and provide aeration in the soil. In sloping land, prevention of surface soil erosion is very important, and, therefore, it is necessary to cover the surface with a species of grass such as Italian ryegrass.
Planting Season
There are two planting seasons, in spring and in autumn. Spring planting is done at the beginning of March, before commencement of active growth. Autumn planting, carried out between the beginning of October and the end of November, is superior to spring planting for better growth of vines.
Spacing
It is important to enlarge the canopy after planting using a horizontal trellis method of support for training the vines. The canopy enlargement depends on the kinds of cultivars, pruning methods, soil fertility, planting material quality (virus-free), cultivation style (such as root-restriction cultivation), and rootstocks. The standard planting density for ‘Delaware’ used to be between 80 and 240/ha, but proper spacing has recently been examined under different conditions.
5. CARE AND MANAGEMENT OF VINEYARDS
5.1 Training and Pruning of Plants
Most vineyards are furnished with a horizontal trellis (Fig. 5). The horizontal trellis is very popular since most of the grape-growing areas are hit by typhoons almost every year. A horizontal trellis is more effective in minimizing wind damage. The rainy season through June and early July coincides with the period of berry enlargement or ripening in open cultures. The shortage of sunshine hours and the humid conditions tend to retard berry development and promote fungal diseases. Leaves on a horizontal trellis can utilize the sunshine more efficiently and minimize the spread of diseases. Shoot growth also tends to be too vigorous to ensure good berry set and berry growth during the warm and wet rainy season. Enlargement of the canopy to control shoot growth can be easily performed in this training system. Grapevine management, such as cluster trimming, GA treatment, and berry thinning, which are indispensable in order to produce high quality grape bunches, is easily conducted under a horizontal trellis. Recently, a flexible horizontal trellis that allows adjustment of the trellis angle to the stature of the grower has been developed to save labour hours and enhance management efficiency under protected culture (Fig. 6).
There are two principal pruning methods, namely, short cane pruning (severe spur-pruning) and long cane pruning. The objectives of short cane pruning are to leave only 2 to 3 buds on one lateral shoot and maintain straight primary shoots. This pruning method has been mainly used in the western part of Japan. This kind of heavy pruning is easy for farmers to carry out without using a special technique. On the other hand, one year old canes that elongated in the previous year are pruned leaving several buds in the long cane pruning method. This pruning system has been used in the eastern areas of Japan.
Figure 5. The Horizontal Trellis System
Figure 6. A Flexible Horizontal Trellis with Root-Restricted Culture Under a Protected Culture
5.2 Application of manure and fertilizers
Standard amounts of manure and fertilizers used in the Yamanashi area are shown in Table 5. The amount of fertilizer depends on the soil type, the age of plants and the cultivar. Young vines, virus-free vines, and tetraploid cultivars should receive less nitrogen to suppress excess growth because they exhibit very vigorous cane growth. Most fertilizer is supplied as basal fertilizer between October and the beginning of November.
Table 5. Standard Amounts of Fertilizers Used in Some Major Cultivars (Yamanashi, 1989)
|
Cultivars
|
Yield (t/ha) |
Amount of Fertilizer(kg/ha) |
Amount of Manure (t/ha)
|
|||
|
|
N |
P2O5 |
K2O |
CaO, MgO |
||
|
Delaware |
15 |
150-170 |
170-180 |
150 |
800 |
15 |
|
Kyoho, etc.(tetraploidy) |
12-14 |
60 |
150 |
120 |
1000-1500 |
15 |
|
Neo MuscatKaiji |
18-22 |
160-200 |
150-170 |
150-160 |
1500 |
20 |
|
Muscat Bailey A Kosyu |
22-24 |
130-210 |
190-260 |
130-150 |
1000-2000 |
15 |
There are three different kinds of surface soil management. One is sod culture, particularly in sloping land, because grass prevents surface soil erosion during the rainy season. Grass supplies organic matter into the soil, and grass roots also improve the physical conditions in the soil. However, grapevines and grass sometimes compete aggressively for water and nutrients under conditions of drought stress in shallow soils.
Another management method is known as clean culture, mainly used in flat vineyards. Herbicides such as ‘glyphosate (isopropylamine)’ and ‘diquat paraquat’ are sprayed in spring and summer. However, the soil surface surrounding the main cane is covered with straw to prevent vines from drought stress and nutrient competition and which also supply organic matter.
5.4 Irrigation
Grapevines require the most amount of water during two periods of growth, usually before germination and during berry enlargement. On the contrary, water is restricted to improve berry quality during the maturation period. The number of irrigation’s depends on the soil type and the growth stage of the crop. About 30 mm of water per irrigation is sufficient during the summer season for a vineyard on clayey soil. Vineyards on clayey soils are watered at longer intervals than those on sandy soils. Soil moisture should be recorded with a pF meter and kept between pF2.3 and 2.5. Use of sprinklers is the most common irrigation system in Japan. In addition to irrigation, it is possible to use the sprinklers to spray some chemicals on a flat canopy developed on a horizontal trellis. Drip-irrigation and misting nozzles are also used under protected culture.
5.5 Pests and Diseases
a) Pests
The main pests of grapes in Japan include yellow tea thrips, grape borer, grape clearwing moth, grape phylloxera, grape leafhopper, swift moth, mealy bugs and mites. Thrips and borers are notorious pests in Japan. In warmer areas, the occurrence of yellow tea thrips is 7 to 8 times per growing season, but it is 5 to 6 times in cooler areas of Japan. Thrips over-winter under grape bark, dropped leaves, or in soil. Timely sprays are given before blooming, after flower dropping, and during the maximum occurrence period, from mid-July to early-September. Synthesized pyrethroid can be sprayed to effectively control this pest.
b) Diseases
Vitis vinifera is subject to numerous diseases. Some of them cause serious problems in all grape-growing areas, while some others are of local importance. Among fungal diseases of leaves and fruit, powdery mildew, downy mildew, anthracnose, grey mold, and ripe rot are prevalent. Crown goal is an important bacterial disease. Leafroll is caused by viruses GLRaV-1 and GLRaV-3 which have been detected with ELISA. It is reported that both of them propagate and spread through grafting. In addition, GLRaV-3 is transmitted through comstock mealy bug (Pseudococcus comstcki), and GLRaV-1 has shown evidence of sap transmission. In Japan, several cultivars show latent infection by corky bark, a kind of rugose wood complex. Although damage is not serious, grapevine berry inner necrosis caused by GINV (grapevine berry inner necrosis virus) was found in Ibaragi Prefecture in 1984. This virus shows graft and sap transmission. Yellow speckles caused by viroids have not been detected in Japan so far. Many cultivars show lateral infection with Fleck that is thought to cause Aji-nashika (low-sugar berry) disease.
5.6 Physiological Disorders
a) Shatter (floret dropping)
This disorder is a phenomenon characterized by florets dropping after blooming. Lack of proper fertilization, bad nutrient conditions, and physiological stress (water deficit or high temperature) cause florets to drop. Several cultivars, such as ‘Kyoho,’ ‘Pione,’ and ‘Muscat of Alexandria,’ are susceptible to this type of disorder.
b) Sunscald
Sunscald has been mainly observed on ‘Muscat of Alexandria’ under glasshouse conditions from the late first stage to the late second stage of berry growth. There are different kinds of disorders on the berry surface, including blotch, berry shrink, and sunburn. These disorders are commonly caused by denaturation of the vascular bundle. The sunscald phenomenon might be related to ‘water berry’ or ‘stem necrosis,’ which are also caused by a disorder of the vascular bundle. Therefore, the mechanism of this disorder needs to be clarified as soon as possible.
c) Berry Cracking
Cracking during maturation depends on cultivars and cultivation conditions. ‘Delaware,’ ‘Olympia,’ and ‘Red queen’ crack easily. Berry cracking is observed in diluvial soil more frequently than in alluvial or volcanic ash soils. Research on grape skin indicates that cracking is due to inferior texture of the skin, the long oval shape of the berry with a pericarp that can be easily distorted, and a thinner cell wall of the sub-epidermal cell layer. It is important to avoid wet soil conditions after long periods of water deficit during the growth stage to protect berries from cracking.
In addition to these disorders of the berry, low berry colouration is a problem caused by high temperature during the maturation stage, heavy fruit load, bad nutrient conditions, virus infections, or low light intensity, among others.
d) Less Growth due to Cold Damage
This is a kind of cane growth disorder. Less sprouting and slow growth of canes are observed in the spring, particularly in cold areas, due to cold damage in association with water deficit. It is therefore necessary to improve freezing resistance of both cultivars and rootstocks. New cultivars with high freezing tolerance bred by the National Institute of Fruit Tree Science (NIFTS), such as ‘North Red’ and ‘North Black,’ have been introduced in northern areas of Japan.
5.7 Grape Quality Improvement and New Cultivation Systems
a) Inducing Seedless Grapes by GA Treatment
Consumers prefer seedless grapes because they are easy to eat. Success in producing seedless ‘Delaware’ grapes with GA application remarkably increased the consumption of this kind of grape. Fruit clusters are dipped with 100 ppm of GA solution 2 weeks before blooming and again after blooming. The pre-bloom treatment makes the berries seedless, while the post-bloom application stimulates berry enlargement. These treatments cost about 300,000 yen (US$ 2,800) for the chemicals and require 300 to 400 hours of labour per hectare. Seedless ‘Muscat Bailey A’ grapes have also been successfully produced by the same treatment. For ‘Kyoho’ and ‘Pione,’ a modified treatment with lower concentration of GA and a later application time has been developed.
b) Prolonged Period of Fruit Supply by Protected Cultivation and New Storage Systems
Fruit harvesting under an open culture begins in late July or early August for early cultivars, followed by mid-season cultivars in late August and October, and ending in late December for late cultivars. Harvest time is markedly advanced in heated houses and grapes marketed earlier are sold at a higher price. Application of heating can begin as early as late November or December. In such cases, fruit is harvested from April to May. In vines heated in late January or February, fruit is harvested from May to July or August.
Cold storage of grape bunches can delay the time of shipping. ‘Kyoho’ bunches can have their marketable period extended by 30-50 days when wrapped with plastic films and stored at 0o C and 80 percent relative humidity. New storage methods with minus ion and ozone that were developed by NIFTS can tremendously extend the storage period by over 70 days.
Although heated cultivation and new storage systems can extend fruit supply from early April to December, it is difficult to supply grapes during the spring season from late January to March. For this reason, the suppression culture, which requires the use of UV-less plastic films, and the double-cropping culture have been examined.
c) Double-cropping
Research on the double-cropping of ‘Muscat of Alexandria’ under protected cultures began in the 1960’s in Japan. Grape growers have been interested in double-cropping to enhance yield and income. The first cropping is in late June or early July, and the second one is in December or January, when high prices are expected. In this cultivation, specific techniques such as temperature control, breaking of dormancy, pruning, long-day treatment by fluorescent lamps, and enhanced CO2 application are very important. Some growers in Okayama and Shimane prefectures have adopted the double-cropping system.
d) Root-restricted Culture and Soil-less Culture
In addition to developing the protected cultivation techniques, root-restricted culture and box culture have been examined (see Fig. 6). These culture systems promote good control of vine vigour, stable production, and fruit quality improvement.
In a soil-less culture, a hydro-culture or artificial solid materials such as a rock wool system are used to produce grapes. This culture has been tested to control grape production automatically.
5.8 Use of Plant-Growth Regulators in the Vineyard
The use of plant-growth regulators in vineyards to control growth and fruit quality has been studied for many years. Several plant regulators have been known to improve grape production in Japan. Gibberellic acid (GA) has been used since the 1950’s to grow seedless grapes and increase berry size. The effect of GA on the promotion of berry maturation and bunch elongation has been observed. Forchlorfenuron (1-(2-chloro-4-pyridyl)-3-phenylurea) liquid has also been used to increase berry size and prevent floret dropping (shatter). Streptomycin is also effective for seedless grape growth and promotion of berry maturation. To prevent florets from dropping, BA (6-N-benzylamino purine) has been used. Calcium carbonate has been employed to reduce the damage by water-soluble copper powder. Forchlorfenuron and BA, ethephon (2-chloroethylphosphnic acid), and mepiquatchloride (1,4-dimetyl piperidinium chloride) are effective to prevent florets from dropping. C-MH (maleic hydrazide choline) has also been used to suppress excess vegetative growth of the cane.
6. HARVESTING AND YIELDS
One of the indicators of the harvest season for table grapes in ‘Kyoho’ is a sugar:acid ratio of 30 to 40 in late August. Fruit quality, including bunch appearance and skin colour, is quite important for shipping in Japan. Using the standard colour chart, skin colour can be determined. Yields depend on cultivars and culture type. An open culture of ‘Kyoho’ has an average yield of 12 to 15 metric tonnes per hectare. The average sugar content (Brix) is 17-18, and the content of tartaric acid is 0.8-0.9. ‘Delaware,’ ‘Campbell early,’ ‘Muscat Bailey A,’ and ‘Neo Muscat’ yield 15 to 18, 24, 23, and 20 to 24 t/ha of table grapes, respectively. Proper yields per hectare are decided by average cane length and the number of new cane per/m2 based on the material production theory through photosynthetic capacity. Heavy fruit load causes low sugar content and a colouration that is not acceptable for table grapes. Moreover, grapes with berry skin disorders do not sell or must be sold at a low price. Proper yields promise high fruit quality and income.
7. MARKETING
In 1997, total grape production was 250,900 metric tonnes, 87.4, 11.0, 1.4, and 0.2 being the percentages for the production of table grapes, wine, juice, and canned fruit, respectively. Only 14 tonnes of table grapes were exported, while 7,649 tonnes were imported in 1997. The grapes marketed earlier were sold at a higher price.
8. POTENTIAL FOR GRAPE-PRODUCTION DEVELOPMENT
Grape production in Japan has not changed dramatically during the past 20 years. However, wine consumption is gradually increasing these days because of its functional components, such as polyphenol, which are thought to be effective in suppressing human senescence. Therefore, high quality wine grape production might develop more in the future. Table grapes must always be of higher quality because higher quality fruit can be sold at a higher price. Stable production of high quality table grapes brings more income to farmers. The potential exists for the development of exports to overseas countries, since only 12 metric tonnes of grapes were exported in 1997.
9. CONSTRAINTS IN GRAPE PRODUCTION DEVELOPMENT
Although wine consumption has increased in recent years, the total consumption of not only grapes but also all kinds of fruit has been continuously on the decline in the last two decades. Grape farmers who have small grape farms cannot increase their vineyard area or their production to improve their income further. This consumption decrease is one of the biggest constraints in Japan. A second problem is that, as they age, most farmers suffer the consequences of the long, hard, and intensive labour required for berry thinning and bunch trimming, among other tasks that are necessary to produce high quality grapes. The requirement of intensive labour is the reason why there are few young successors. Therefore, new techniques to achieve low-cost production and save labour are required to solve those problems.
10. GOVERNMENT POLICIES AND PLANS FOR GRAPE RESEARCH AND DEVELOPMENT
Breeding Objectives
The major breeding objectives are to select excellent cultivars adapted to Japanese climatic conditions. Seedlessness, large berry size, good appearance, and high quality are the principal considerations for table grapes. The use of triploid or tetraploid cultivars is advantageous. For wine grapes, to improve the wine quality of old Japanese cultivars, back crossing of V. vinifera grape to these cultivars is being carried out as the demand for wine increases. The selections are propagated and distributed to several research stations with different climatic and soil conditions for multi-location testing. Productivity, fruit quality and wine quality are tested to select promising cultivars for both table and wine grapes.
Disease resistance is another important objective. Most grape cultivars are susceptible to many diseases. Inoculation techniques have been evaluated in downy mildew, anthracnose, ripe rot, and grey mold in Japan.
Biotechnology
The development of biotechnology is very important to improve grape cultivars. Grapes are heterozygous plants, and genetic analysis for important agronomic traits has not made appreciable progress. Haploid plants are of considerable value for genetic analysis and crop improvement. Protoplast fusion and somatic hybridization enable the achievement of wide hybridization and partial gene transfer. Although cross-hybridization is generally used for plant breeding, it results in plants inheriting both favourable and unfavourable characters at the same time. On the other hand, only the target gene can be transferred to the plant by means of genetic engineering. Gene-delivery systems such as the Agrobacterium-mediated system, electroporation, and DNA-coated microprojectiles can be used for this purpose. The analysis of DNA, such as RAPD, RFLP, and AFLP, is an important technique for the classification, identification, and development of molecular markers and the isolation of useful genes in grape breeding.
Physiological Aspects
A stable annual production of high quality fruit under different cultivation systems is the most important goal for both table and wine grapes. It is important to research stable berry set, control maturation, and skin colour based on plant hormone movement, water relations, photo-assimilate translocation, and gene analysis in grapevines.
Low-cost Production and New Technology for Labour Saving Culture
To achieve high quality table grapes, berry thinning and cluster trimming are the most labour-demanding management tasks. It is necessary to reduce the amount of labour and improve the efficiency of labour productivity to produce grapes at a lower cost. However, it is quite difficult to do berry thinning and cluster trimming automatically or mechanically, so breeders have been trying to breed a new cultivar that does not require berry thinning or cluster trimming.
Environmental Concerns
Fewer chemicals and less nutrients should be supplied to orchards to preserve the environment. A biological protection system using natural enemies, for example, will be researched to prevent grapevines from diseases and pests. The amount of nitrogen fertilizer used should also be examined and reviewed again from the point of view of environment preservation and plant nutrition effect.
11. CONCLUSIONS
To develop the grape industry, grape farmers try to produce a stable yield of high quality fruit. Research scientists such as plant physiologists, grape breeders, molecular biologists, and pest and disease researchers, working at both National and Prefectural Institutes of grapes in Japan, must solve the grape production problems mentioned above. In addition to that, more cooperation among research scientists, grape farmers, the fruit-produce cooperative societies, and fruit-market workers is important for the improvement of grape production strategies.
