Vitis vinifera (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Vitis vinifera L.

Protologue: Sp. Pl.: 202 (1753).

Family: Vitaceae

Chromosome number: 2n= 38

Vernacular names

• Grape (En)
• Vigne, raisin (Fr)
• Indonesia: buah anggur
• Malaysia: anggur
• Philippines: ubas
• Burma: sa-pyit
• Cambodia: trâpèang' baay chuu
• Laos: 'angunx
• Thailand: a-ngun
• Vietnam: nho.

Origin and geographic distribution

The numerous grape cultivars of the Old World are thought to derive from a single wild species, V. vinifera , occurring from north-eastern Afghanistan to the southern borders of the Black Sea and the Caspian Sea. After domestication there (around 4000 BC), cultivation spread to the Mediterranean area, western Europe, India, China and Japan. Grape was introduced to the New World at the time of discovery and spread with the Spanish and Portuguese voyages. When introduced to new areas, it often hybridized with native Vitis species to produce cultivars adapted to local environments (e.g. American, Chinese, Japanese cultivars). At present grapes are grown all over the world, often as hybrids of unknown identity.

Uses

Most of the world's grapes are made into wine, the use of the fresh and the dried fruit (raisins) coming second and third in importance. Grape juice is another product. In South-East Asia only the use as table grape is important, although some wine is produced in Thailand and wine grapes are being evaluated in the drier parts of north and north-east Thailand. When thinning the bunches the Thais pickle the thinned berries.

Production and international trade

The grape is the world's most important fruit crop in area, production and value, and this is reflected in specific names for grape growing - viticulture- and wine making - oenology. Two-thirds of world production comes from Europe: Spain, Italy and France being the leading producers. Overproduction in Europe is largely responsible for a decline in world acreage and yearly production, from 9.4 million ha and 66 million t averaged over 1979-1981, to 8.4 million ha and 60 million t in 1988. There is a lively international trade in the fresh fruit as well as in the main products, raisins and wine. Fresh grapes are even sent from the southern hemisphere to Europe; raisin exports come mainly from California and the Middle East. Relative newcomers in the gigantic international wine trade, such as the United States, Australia and South Africa, are assuming increasing importance.

In South-East Asia Thailand produced 25 000-30 000 t grapes annually over 1984-88 from an area of about 3300 ha, considerably lower figures than for the early 1980s. Indonesia comes second with over 2000 t (nearly all from Bali) in 1984. At the time the area tended to double each year, possibly leading to corresponding increments in production. In the Philippines the grape is a minor but expanding crop with nearly 700 t from 140 ha in 1987. Production in South-East Asia is by and large for the home market, but Thailand exports some grapes - 565 t in 1986 - mainly to Singapore, Malaysia, Brunei, Hong Kong and Japan.

Properties

Analyses in Thailand show the following composition of the fruit per 100 g edible portion: water 86 g, protein 0.5 g, fat 0.3 g, carbohydrates 12.8 g, fibre 0.9 g, Ca 9 mg, Fe 0.06 mg, P 20 mg, vitamin A 83 IU, vitamin B1 0.10 mg, vitamin B2 0.06 mg, vitamin C 3 mg and niacin 0.2 mg.

Description

• Vigorous, climbing woody vine, 15-20 m or more tall, but in cultivation drastically restricted by pruning. Tendrils forked, produced intermittently at two out of three vegetative nodes, opposite the leaves.
• Leaves simple, circular or circular-ovate in outline, 5-25 cm wide, long stalked, palmately lobed and coarsely toothed.
• Inflorescences in dense thyrses that take the place of tendrils; flowers fragrant, 5-merous, actually or functionally unisexual, yellow-green, small; calyx 5-lobed; corolla with 5 petals, up to 5 mm long, joined at the tip, forming a cap (calyptra) which falls off at anthesis; disk glanduliferous and prominent.
• Fruit a berry, ellipsoid to globose, 6-25 mm long, dark blue-purple, red, green or yellow, juicy, sweet or sour.
• Seeds 3-4, pyriform.

Growth and development

At fruit maturity the seeds are dormant. Dormancy is broken by low temperature, after which the seeds germinate within a month. The vine is a trailing shoot which grows continuously. As the shoot extends, sylleptic shoots emerge in many leaf axils. Their vigour is checked by apical dominance, but competition ultimately brings one or several favourably placed laterals to dominance, arresting extension growth of the main shoot. Meanwhile, the succulent vine turns woody and leaves are shed as woodiness progresses.

The continuous extension growth, perpetuated by laterals, results in a typical liana-habit for untrained vines in the tropics: very long, thin, woody stems supporting a tangle of growing shoots. Since the sylleptic shoots produce virtually only tendrils where the inflorescences should be, such unattended vines are unproductive. In addition to the bud which gives rise to the sylleptic shoot, there is a plump main bud in each leaf axil; it is clearly visible by the time the subtending leaf has expanded. This bud reaches full development before the leaf falls and the node becomes woody. By that time it is covered by bud scales (which also protect 2 accessory buds, the main bud being in fact a compound bud) and all the initials for a shoot with 6-9 nodes have been laid down, in many cases including primordia for one, two or - exceptionally - 3-4 inflorescences. The bud then gradually goes dormant. In the vine's natural environment the dormancy is broken by the short days and low temperatures of winter (which also cause leaf abscission and death of non-woody shoot tips). When the growing conditions improve in spring, the main buds break, many producing flowering shoots.

Four to eight weeks with daylengths of less than 14 h suffice to break dormancy, so that main buds on cultivated vines in the tropics are ready to leaf out by the time the fruit of the current crop matures. However, they will only do so if pruning eliminates correlative inhibition by actively growing shoots. Apparently, viability of the main buds declines in the tropics, for if pruning is delayed, budbreak is poorer. Buds which do not break after pruning almost certainly will not break following subsequent pruning rounds. Thus, successful grape cultivation in the tropics is only possible if the main buds are activated soon after they come out of their dormancy (perhaps also just before they go dormant, as suggested by very short crop cycles in Taiwan). That is why crop cycles of 6 months duration (2 crops per year) are common practice.

On a shoot derived from a main bud, the main buds at the first and second nodes usually lack flower initials: at the third and higher nodes the percentage of fruitful buds increases and then falls again at still higher node numbers, say beyond node 7 or 10. This "fertility gradient" along successive nodes varies in different growing seasons, but it is characteristic for each cultivar. Cultivars with a high percentage of fruitful buds at the basal nodes may bear a good crop after short pruning (spur pruning), others require long pruning (cane pruning). To complicate matters, main buds on the nodes of sylleptic shoots have another fertility gradient, the basal nodes usually bearing fruitful buds. Thus the sylleptic shoots differ from the proleptic shoots mainly in 3 respects:

• dormancy plays no role in their formation; they are ready to leaf out as soon as the subtending leaf unfolds;

• they generally do not flower (if they do, the inflorescences are often half tendril, half flower cluster);

• the main buds at their basal nodes are predominantly fruitful.

These differences are important, because the sylleptic shoots - called "laterals" in viticulture - play a prominent role in vine training and pruning in the tropics.

When vines are pruned, main buds leaf out after about 15 days; about 6 weeks later the inflorescences on the new shoots reach anthesis. Even before anthesis, floral differentiation for the next crop has already started in the main buds. In the tropics budbreak is often poor and largely limited to one or two buds nearest the pruning cut. Consequently, long cane sections are devoid of side shoots, leading to sparse foliation and loss of vitality of the vine.

Dioecy is common in Vitis L., but cultivars usually have perfect flowers with functional stamens as well as pistils. In V. rotundifolia Michaux female flowering clones are coming to the fore; these cultivars require hermaphrodite or male pollinators. Anthesis starts from 5 am and continues till 10 am. Stigma receptivity lasts for 2 days, before and during anthesis. Both self- and cross-pollination lead to fruit set. Wind pollination dominates; insects play a minor part in pollen transfer.

In South-East Asia the period from pruning to harvest is about 3.5-4.5 months, depending on the cultivar. The growth of the berries can be described by a double sigmoid curve. If ripe berries are not picked, they shrivel and dry on the bunch (unless they fall prey to birds, moulds, etc.).

Other botanical information

The genus Vitis contains about 60 species, but botanical knowledge is incomplete. All known Vitis species can be easily crossed experimentally, producing vigorous and fertile hybrids; hybridization also occurs in natural populations. Other genera like Muscadinia Small and Ampelocissus Planch. are also involved. It seems quite certain that in cultivars grown in South-East Asia, traits derived from Vitis labrusca L. and Vitis rotundifolia complement to a greater or lesser extent those contributed by V. vinifera.

V. labrusca originates from the United States; it requires relatively humid conditions for good growth and is more resistant to fungus diseases. Its berries are large (15-25 mm diameter), usually blackish with a rather thick skin, and the flesh has a distinctive pungent odour and flavour. Cultivars of this species, collectively termed Labruscans, are important as producers of dessert grapes. V. rotundifolia (also named Muscadinia rotundifolia Small) originates in the south-eastern United States and in Mexico where these hardy muscadine grapes were already cultivated in the 17th Century. The species was intensively used in crosses with V. vinifera to improve the disease resistance of V. vinifera and the fruit quality of V. rotundifolia, resulting in numerous hybrid cultivars.

Cultivars which have proved successful in the tropics include "White Malaga" (fairly late, green-fruited; the leading cv. in Thailand, now being replaced by what probably is a mutant: "Long White Malaga"), "Alphonse Lavallée" (syn. "Ribier", fairly late, jet-black fruit), "Cardinal" (very early, bright red fruit), "Kyoho" (late, red-fruited; leading cv. in Japan and Taiwan), "Perlee" (green, seedless), "Isabella" (syn. "Bangalore Blue", Labruscan cv.). Cultivars in Indonesia bear local names (e.g. "Bali", "Probolinggo Biru-81", "Banjersari-45" and "Banjersari-56"), the original names having been lost.

Ecology

At high latitudes the main requirement is a long enough growing season with much sun and a sufficient heat sum in degree-days to ripen the berries. The winter is not critical as long as it is not very cold (-20°C is the approximate limit), but spring frosts of -3 to -5°C after the resumption of growth can destroy the young shoots, including the inflorescences. Temperatures of 25-30°C are optimal for shoot and berry growth. Light requirements are high, but whereas the leaves should be exposed, they should shield the fruit against sunscorch. That is why overhead trellises are preferred in the tropics instead of the hedge-like trellis systems at high latitudes (where the sun's zenith remains low). Vineyards require protection against strong winds.

Humid conditions during the growing season require a strenuous battle against fungus diseases in all V. vinifera cultivars. This is a problem in tropical monsoon climates where the wet season cannot be skipped since prolonged dormancy leads to poor budbreak. Temperatures above the optimum during a sunny tropical dry season should be moderated by transpiration cooling, which means an uninterrupted water supply. On the other hand, the grape is able to produce a fair crop in the absence of irrigation, even in semi-arid regions, since the extensive root system sustains growth where other crops suffer severe drought stress. At elevations above 1200 m in the tropics temperatures become marginal for grape growth and fruit quality.

The grape grows on almost any type of soil, light or heavy, deep or shallow, fertile or not, but responds to better soils with higher yields. Light soils promote early ripening and a high sugar content. Fertility is not as important as a soil structure that favours extensive root development. V. vinifera cultivars require deeper soils than American grapes. Flooding is not tolerated; it can kill a vineyard within 2 days. The soil pH should be between 5 and 8; values slightly below 7 are considered best.

Propagation and planting

Grape seedlings are not true to type. As cuttings root easily, they offer a simple way of clonal propagation. Grafting or budding is also possible and there is a wide choice of rootstocks selected or bred for pest, drought or salinity tolerance; rootstocks also vary in vigour and suitability for light or heavy soils. Cuttings are generally used in South-East Asia; in Thailand chip-budding is commonly practised on "Solonix × Othello 1613", a rootstock with resistance to grape phylloxera and most strains of rootknot nematodes.

Hardwood cuttings are taken from apparently healthy, productive vines when the vineyard is pruned. Sturdy canes with fairly short internodes and well-developed buds are best. The lower cut is made at a node, the upper cut between the fourth and fifth nodes above. The Thai rootstock is also propagated from cuttings; the stocks can be budded when the budwood bears fully developed main buds.

A very wide range of plant spacings is employed in viticulture as spacing depends on the training system as well as on vine vigour. In Thailand's central delta, paddy fields are converted into raised beds, separated by ditches 8 m apart to provide drainage in the wet season and irrigation water in the dry season. Each bed carries 2 rows of vines 4-5 m apart and the vines are spaced 3-3.5 m in the row, giving densities of 830-700 vines per ha. In Indonesia and the Philippines the density often exceeds 1000 vines/ha.

Husbandry

Training and pruning are very important in viticulture. "Training" involves forming the permanent framework of the vine, and "pruning" is cutting back new growth to maintain the established form and to regulate fruiting. Pruning intensity varies with the vigour of the plant and the anticipated fruitfulness of the remaining buds; it also depends on whether the crop load will be further regulated by cluster and/or berry thinning.

Training requires trellising; in the tropics overhead trellises - pergolas or bowers - and T-trellises are generally preferred. In Indonesia live posts of Lannea coromandelica (Houtt.) Merr. (synonym L. grandis (Dennst.) Engl., "kayu kuda"), and bamboo cross-bars provide a relatively cheap support structure for the overhead wires. A discussion of training and pruning is beyond the scope of this volume, but the nature of the problems and the main deviations from the situation at higher latitudes are described.

"Bare arms" are a major problem in vine training in the tropics. Whereas the bearing arms could carry a cane at every node, long sections of the arms tend to be bare or carry laterals which are too light to qualify as canes. To make up for the missing canes, the bearing arms are allowed to grow very long and are tied along the wires in orderly loops. Thus the bearing arms overlap to arrive at an acceptable number of canes per square metre. The problem can be prevented simply by pinching the tips of these arms repeatedly as they are growing, in order to force the laterals at each node into growth. Only when enough laterals leaf out with adequate vigour should the arms be allowed to extend. Pinching slows down the formation of the bearing arms, but it produces a compact frame well-clad with canes which, after pruning, will produce the first bearing shoots. More importantly, the vitality and longevity of the vines is improved because the distance between roots and shoots remains minimal.

Throughout the training phase everything is done to promote vine vigour because the most demanding task - formation of a high percentage of strong laterals - comes last. If vigour is adequate, training can be completed in about one year.

The training phase is followed by the bearing phase during which pruning initiates each crop cycle. In Thailand "Cardinal" is spur-pruned to 3-4 nodes, "Loose Perlette" is cane-pruned leaving 7-12 nodes, and pruning severity is intermediate for "White Malaga" where 5-6 nodes are left. These figures suggest well-defined pruning recipes, but in fact pruning in the tropics is not as exact and effective as it is at higher latitudes. The reason is that the problem of bare arms in the training phase is matched by barren spur complexes during the pruning phase, owing to poor and erratic budbreak.

Following pruning, budbreak proceeds slowly from distal to basal parts; a low percentage of the buds break, the distal buds being most responsive. With two crop cycles per year and budbreak largely limited to buds nearest the pruning cuts, the spurs quickly become more complex and extend further outwards from the arms. There are few opportunities to rejuvenate a spur complex by cutting back close to the arm, since axillary buds on older wood deteriorate and adventitious buds are rare. Shortage of shoots and the increasing distance between shoots and roots leads to a rapid decline of vine vitality; in Thailand vineyards have to be written off within 7-12 years!

A variety of growing techniques is employed to stimulate budbreak. Water stress which builds up during the harvest period is relieved by irrigation as soon as the vines are pruned: nutrients are applied at the same time. Canes are generally pruned shorter than at higher latitudes in order to stay closer to the arms. Individual buds may be "nicked" by making an incision in the node above the bud to eliminate correlative inhibition. A number of chemicals have been employed to improve budbreak. In the 1980s these were all replaced by calcium cyanamide or hydrogen cyanamide. Cyanamide is safe and particularly effective on cultivars with a low percentage of breaking buds; it may have a strong impact on tropical viticulture.

During the rainy season it is difficult to maintain vine health and to produce fruit of good quality. It may be better to sacrifice the rainy season crop by applying very short pruning, e.g. to a single node, in order to obtain shoots which are predominantly unfruitful. Moreover, in so doing, the extension of the spur complex is minimal.

Pruning at the beginning of each crop cycle is supplemented by pinching or cutting back the strongest shoots to allow weaker neighbours to catch up, the aim being that all shoots should be equal. This can be done when the shoots are being tied to the trellis. Where the response to pruning is unpredictable, as in the tropics, thinning of flowers and/or fruit is a valuable means of correcting the balance between growth and fruiting. Overbearing not only weakens the vine, but also affects fruit quality (less sugar accumulates in the berries). Moreover, thinning helps to produce more open clusters (less susceptible to rot) of regular shape (easier to pack). Flower thinning consists of removing the uppermost inflorescence on all or part of the shoots bearing two or more inflorescences. The bunches can be thinned shortly after fruit set to improve bunch shape, e.g. by clipping the long tip or projecting shoulder of a bunch. Individual berries are clipped if, after natural berry drop, defective or small berries remain, or if the cluster is still too compact.

Under the influence of short daylength the vine habit becomes more compact, including the bunches. Growers in Thailand dip bunches in a gibberellic acid solution (GA₃, 10-50 mg/l) to force them to grow out; the treatment also increases berry size. Bunches are dipped twice: 7 days after the vineyard reaches the 80% bloom stage and 7 days later.

Vineyards are usually clean-cultivated, but growing a green manure crop, for instance during the rainy season, is recommended: the grape is partial to organic matter. Grapes can extract stored soil moisture to produce a fair crop, but irrigation gives higher yields and better crop regulation and is a common practice in the tropics. Water is very important at the critical stages of flowering and fruit set. Irrigation is stopped from a few weeks before harvest until the next pruning; this is to improve fruit quality and budbreak.

Fertilizer requirements are in the order of 150 kg N at good yield levels, 50-80 kg P₂O₅ and 0-200 kg K₂O per ha, depending on the soil. In Thailand, fertilizer is applied one month after planting and twice during each crop cycle: 7-15 days and 45 days after pruning. In the tropics manure is often applied in generous quantities when the vines have been pruned. A new vineyard may benefit from inoculation with grape mycorrhiza (Glomus spp.) - using soil from good maize fields - to facilitate uptake of phosphorus.

Minor nutrients may need attention. Iron chlorosis is common on calcareous soils and magnesium, zinc and boron deficiencies, as well as toxic boron levels, have been reported from tropical regions. For foliar analysis, leaf petioles are used, preferably during bloom, but recommended levels differ so much in different countries that they cannot be simply copied for South-East Asia.

Diseases and pests

Diseases and pests are a major limiting factor for grape growing, in the tropics as well as elsewhere. The main fungus diseases are downy mildew (Plasmopara viticola), anthracnose (Colletotrichum gloeosporioides) and powdery mildew (Oidium tuckeri). During the rainy season in Thailand 2 or 3 treatments - mainly with copper and sulphur fungicides - may be applied each week. Thus, there is a real danger of copper concentrations reaching toxic levels in the soil! This intensive control programme also controls several lesser diseases.

Virus diseases undermine vigour, productivity and fruit quality of vineyards. Control of viruses - and other graft-transmissible diseases - is based on the use of certified clean planting material. As such material is not yet available in South-East Asia, it is to be expected that virus problems will eventually become an important issue.

A host of pests attacks grapes, but their occurrence is more incidental and there is no routine spray programme against leaf hoppers, flea beetles, thrips, cutworms, red spider mites, etc. If heavy cracking soils are infected with grape phylloxera (Viteus vitifolii), vineyards can only be successful if resistant rootstocks are used. Resistant rootstocks also solve the problem of nematodes, which spread quickly on lighter porous soils and transmit virus diseases. Constant vigilance may be required to scare off birds and bats when the fruit ripens.

Harvesting

Grapes do not ripen after harvest, so they should not be picked until mature. Ripening is largely a matter of increasing sugar content and decreasing acid content, so that the sugar:acid ratio is a useful maturity index. The colour and flavour of the berries and the appearance of the cluster stem (turning to a light straw colour) are more subjective criteria for maturity. Two or three pickings at intervals of a few days are usually needed to clear the crop.

The picker grasps the cluster stem and cuts it with a knife or scissors near its point of attachment to the cane. Before putting the cluster in the basket or tray the picker inspects it and clips off any defective berries.

Yield

Yields of 80-90 t/ha per year have been reported from south India, but such yields are excessive, resulting in low sugar content and rapid decline of the vineyard. In Taiwan summer crops of 30-60 t/ha are common, but low sugar levels and very light winter crops indicate that this is too much; the aim is to lower yield in summer in favour of the winter crop.

It would seem that yields of 10-30 t of good quality fruit per ha, depending on cultivar and crop season, are sustainable in the tropics. With 2 crops per year or 5 crops in 2 years, this is outstanding productivity, both in comparison with other fruits and compared with grape yields at higher latitudes. In Indonesia 20-30 kg per vine is considered a good crop, and actual average yields in Thailand ranged from 8.5-12 t per ha per year over 1982-1987.

Handling after harvest

The harvested bunches are placed with the bunch stems more or less upright in bamboo baskets or wooden trays lined with banana leaves or paper; containers hold 10-15 kg. Depending on the cultivar, grapes can be kept in cool storage at 1-2°C for 3-6 months at a relative humidity of 90-95%. In the tropics this may be helpful to maintain supplies through the wet season. For long-term storage the fruit is fumigated with SO₂ soon after harvest and at intervals during storage to reduce spoilage by decay organisms. The firm skin of most table grape cultivars allows for a surprisingly long shelf life considering the nature of the product, but utmost care in handling is important to avoid skin rupture.

Genetic resources and breeding

Grape collections in South-East Asia are maintained in Thailand (Nakorn Pathom, Chiang Mai; including wine grapes), and Indonesia (Banjersari - East Java). These collections are quite modest compared with those in leading viticultural countries, e.g. at Davis, United States and Merbein, Australia. Breeding of grape cultivars and rootstocks is conducted at these large viticultural centres, which are also trying to create some order in the confused nomenclature of cultivars, and are increasingly carrying out clonal selection programmes within cultivars. For tropical viticulture, the emphasis in breeding programmes on disease resistance is very relevant. It may be worthwhile to screen the tropical Vitis spp. - including those which are indigenous in South-East Asia - for their potential as breeding parents.

Prospects

Viticulture has only recently taken hold in the tropics. Although the achievements in countries such as India, Thailand and Venezuela are impressive, the principles underlying successful production are not yet very clear. There appears to be immense scope for expansion of tropical viticulture, in the drier parts of South-East Asia too, provided that adequate solutions can be found for:

• the unpredictable budbreak coupled with ill-defined training;

• the imbalance between growth and fruiting;

• the awkward dilemmas posed by the rainy season.

A better understanding of the crop in tropical environments should provide the clues to eliminate the first two constraints. The problems with disease control and fruit quality during the rainy season may be much harder to solve; breeding offers the best perspective. Progress in these areas will also greatly enhance the chances for producing wine grapes and raisins in the tropics.

The initial investment in a vineyard is high, but it takes only 2 years or less to produce the first substantial crop. Large gains in productivity can still be made, to make up for falling prices as supplies increase. South-East Asian markets are undersupplied and it should be possible to compete with the main suppliers, South Africa and Chile. Moreover, grape growing requires much skilled labour, a bonus for rural employment in South-East Asia.

Literature

• Alleweldt, G., 1989. Weintraube [Wine grapes]. In: Rehm, S. (Editor): Spezieller Pflanzenbau in den Tropen und Subtropen. 2nd edition. Band 4. Eugen Ulmer Verlag, Stuttgart. pp. 301-310.
• Chin Ho Lin, 1987. Chemical induction of multiple cropping of grape in Taiwan. Acta Horticulturae 199: 91-99.
• Coronel, R.E., 1983. Promising fruits of the Philippines. College of Agriculture, U.P. at Los Baños, Laguna. pp. 181-203.
• Ho, M.L. & Yang, Y.S., 1982. Viticulture in Taiwan. In: Proceedings of the Joint Seminar of the National Ching Hsing University and California State University, Fresno, on Modern Agricultural Science, July 10-20, 1982, Taichung, Taiwan, Republic of China. pp. 13-22.
• Nilnond, S. & Sukumalanandana, C., 1988. Fruiting response of "White Malaga", "Cardinal" and "Loose Perlette" grapes (Vitis vinifera L.) to some chemicals. ASST Newsletter 21(4): 244-250 (Thai).
• Purnomo, S., 1987. Prospek pengusahaan anggur di Indonesia. [Prospects for grape growing in Indonesia]. Jurnal Litbang Pertanian 6(3): 66-72.
• Shalitin, G., 1973. New approaches to grape growing in the tropics - Grape-vine training and pruning studies in Kenya. Israel Ministry of Agriculture, Centre for International Agricultural Cooperation, Nairobi, Kenya. 28 pp.
• Siriwachirapap, W., Tong-umpai, P., & Ketsa, S., 1985. Harvesting indices of "Cardinal" grapes. Kasetsart Journal (Nat. Sci.) 19: 167-172 (Thai).
• Weaver, R.J., 1976. Grape growing. John Wiley & Sons, New York. 371 pp.

Authors

Saichol Ketsa & E.W.M. Verheij