Everything you need to know about grapes cultivation and harvest! Learn about: 1. Botany of Grapes 2. Origin of Grapes 3. Distribution and Production 4. Climate and Soil 5. Seed Cultivars 6. Propagation 7. Planting Operation 8. Use of Growth Regulators 9. Flowering and Fruiting 10. Thinning 11. Quality Improvement 12. Harvesting and Fruit Handling 13. Diseases and Pests.
Botany of Grapes:
The grape belongs to the family Vitaceae which is made up to 12 genera and about 600 species. The only genus Vitis is containing food plants. This genus is subdivided into 2 subgenera, Muscadinia and Euvitis. The members of Muscadinia have 40 somatic chromosomes, while that of Euvitis, 38. Muscadinia can easily be identified by tight bark that does not shed, simple tendrils, nodes without a diaphragm and small clusters with berries that detach as they mature.
Vinifera has forked tendrils, bark that sheds a diaphragm at the nodes, and elongated clusters with berries that adhere to the pedicels at maturity. It also has intermittent tendrils, thin, smooth shinny leaves with 3, 5 or 7 lobes. Berries are round or oval with edible skins that adhere to the flesh. Grape is berry and edible portion is epicarp and mesocarp.
The genus Vitis consist of about 60 species and only 3 species in Muscadinia. Vitis vinifera produces over 90 per cent of the world’s grapes which are either pure Vinifera or Vinifera hybrids.
Origin of Grapes:
Grapes are one of the most important sub-tropical fruits in the world. The world production of grapes is estimated at 5740 thousand metric tonnes. The major grape producing countries are Italy, France and U.S.A. The fruit is utilized in many ways. The principal product is wine followed by raisins.
It is also used as table grapes, juices and for canning. However in India most of the fruit is used for table purposes. The export of grapes constitutes 2.7% of the fruit exported from India, which amounts to 14 thousand tonnes in quantity and the value of Rs. 60 crore.
The major destinations of export are U.K., Netherlands, UAE, Bangladesh and Germany. The area under grapes in India has been expanding rapidly. It rose from 600 ha in the pre-Partition days to 49.4 thousand ha in 2001-02. The largest area is in Maharashtra (Sangli, Satara, Nasik, Sholapur, Pune, Ahmednagar) followed by Karnataka, Punjab, Tamil Nadu, Andhra Pradesh etc.
Grape cultivation has gained considerable momentum in Punjab, Haryana, Rajasthan and Western U.P. during the last two decades, where area under grapes steadily increased. In North India grapes are grown in a subtropical climate, where the grapevine sheds its leaves in winter and the vegetative growth takes place for only a small part of the year.
Here the yield is low, but the cost of cultivation is much less. Diseases like powdery and downy mildew are rarely found here. Grape is also cultivated in the interior area of Himachal Pradesh called Chini, which is a dry area with an annual rainfall of about 25 cm. This area is more suitable for raisin grapes. India imports substantial quantity of raisins annually. The quality of the grapes grown in India is not good enough for making of raisins, which require 24 to 28 per cent sugars, which includes no sucrose.
The sugar content of grape grown in India varies from 13 to 22 per cent. The sugars do not develop fully in humid weather of South and Central India or the scorching weather at the time of ripening in North India. Attempts have been made to make raisins from grapes grown in Delhi. The varieties Pusa Seedless, Thompson seedless, Kishmis Beli, Delight and Arkavati were found good for raisins.
About 80% of the grapes produced in the world are used for wine making. The important wine grape varieties are white Riesling, Early Muscat etc. In India, wine is made on a small scale from Bangalore Blue grapes. Among commercial varieties Thompson Seedless and the hybrid Aoka Kancha are good for wine making.
Grape originated in the Caspian Sea area and came to India at a very early time. Commercial table grapes belong to the species Vitis vinifera. About 60 species of vitis are reported to grow wild in India. Out of these V. barbata found in Burma, Assam and Bengal, V. rumcisperma found in Assam and Sikkim, V. rugosa found in Burma and Kumaon hills, V. parviflora found in Kashmir gives edible fruits though of poor quality.
Another related fruit, Ampelocissus latifolia is found growing wild in Bihar around Bhagalpur. It has tuberous roots. The plant dies in winter and sprouts again from the tubers when the monsoon starts. The berries are of poor quality and ripen from August to October; the plant is highly resistant to pests and diseases.
Grapes are grown widely in different areas. However, the same variety does not do well under all climatic conditions. For example, Anab-e-Shahi which is the main stay of grape industry in Hyderabad does poorly in North India. The weather during the fruiting season affects the quality of fruit.
Dry weather at the time of flowering is necessary for good fruit set. Rain or humid weather at the time of ripening causes splitting of berries and brings the attack of fungal diseases. In North India, the problem is to get varieties which ripen before the start of the monsoon. Here the maximum temperature at this time goes upto 115°F. Consequently, the berries get sun-scalded and develop a thick skin and have low sugar content.
In western India, there are two crops. One ripens in September-October after the monsoon rains, and is thus of poor quality and is often attacked by mildew. The other ripens in March and is sometimes damaged by occasional frost.
Light soils are ideal for grapes but they can grow in any well drained soil. They can tolerate saline soils successfully. Only the date-palm can tolerate more salts in the soil than grapes. In Madurai, grapes are grown on very poor, gravelly soils.
Distribution and Production of Grapes:
According to the Food and Agriculture Organization (FAO), 75,866 square kilometres of the world are dedicated to grapes. Approximately 71% of world grape production is used for wine, 27% as fresh fruit, and 2% as dried fruit. A portion of grape production goes to producing grape juice to be reconstituted for fruits canned “with no added sugar” and “100% natural”. The area dedicated to vineyards is increasing by about 2% per year.
Grapes grow in clusters of 6 to 300, and can be crimson, black, dark blue, yellow, green and pink. “White” grapes are actually green in color, and are evolutionarily derived from the red grape. Mutations in two regulatory genes of white grapes turn off production of anthocyanins which are responsible for the color of red grapes. Anthocyanins and other pigment chemicals of the larger family of polyphenols in red grapes are responsible for the varying shades of purple in red wines.
Climate and Soil Required for Grapes Cultivatvion:
Grapes are grown commercially in climate ranging from temperate to tropical around the world. The most successful area for grape cultivation is warm temperate zone between 34° North and 45° South latitude. Grapes are grown outside this zone also but in scattered areas. In tropical climate vine is evergreen.
Grape do best under a long, hot, dry and rainless summer with adequate sunshine, followed by a winter cold enough to induce dormancy in the vines. Temperature is considered as a major factor influencing composition and quality of grapes. The total amount of heat received can be expressed in terms of temperature time value called ‘degree days’ or heat units. Certain specific heat units are required for ripening of a particular cultivar.
The early ripening varieties require 1600 heat units whereas the requirement of heat unit for late ripening varieties is 3500. The sugar content of berry generally decreases slightly with increasing altitude. For the production of good quality grapes, dry weather is essential at the time of flowering and when the fruit is developing and maturing.
The vines can tolerate low temperature or frost with little damage in the dormant period. Low temperature in winter helps in leaf fall and the vines enter dormant period. Occurrence of late frost during spring causes damage to sprouting buds.
Heavy and early rains are not good for cultivation of late ripening superior varieties of grapes, as they result into cracking of the berries and spoilage of the crops. Under such conditions, the berries do not develop sweetness and remain insipid. Moist weather also favours the spread of fungus diseases. Regions receiving heavy rainfall area, therefore, are not suited for grape cultivation. Hails during fruiting season may cause considerable damage to the vine.
Labrusca grapes or hybrids having labrusca blood will withstand humid summers and cold winters better than pure Vinifera varieties.
Grapes are adopted to a wide range of soil type and grown on wide variety of soils in different regions both within India and other parts of the world. Grapes have a strong root system, therefore, most of the soil types are considered ideal for its cultivation. The best soil for grape, however, should be sandy loam, well drained and fairly fertile with good amount of organic matter. One should avoid the heavy clays, very shallow soils, poorly drained soils and those that contain high concentration of salts. The grape vines are relatively tolerant to salinity and alkalinity as compared to many other fruit crops. But, excessive lime is harmful for grape growing. The upper salt tolerance limit of grapes has been found to be 0.3 per cent.
The soils that retain water for long do not allow the vines to go into dormancy. Therefore, such soils should not be selected for grape cultivation. Well drained, clay loam, black clay loams and even shallow soils produce successful grape crops. Salt affected, nematode infested and water-logged soils should be avoided. Soils having EC upto 1.5 mmhos/cm, calcium carbonate up to 10 per cent, lime concretion upto 20 per cent and pH upto 8.7 are suitable for successful grape cultivation.
Some grape cultivars can be grown up to 7 mmhos per cm Electrical conductivity. However, salt injury can be expected when conductivity of soil is more than 2.5 mmhos/cm and chloride is more than 10 ppm. This injurious effect of salt is reported more toxic on heavy soils compared with light soils. The exchangeable sodium percentage (ESP) of 45 and above is also injurious to grapes. Anab-e-Shahi is more susceptible to higher ESP than Cheema Sahibi and Bangalore Purple. The cultivar Perlette is more susceptible to salinity, whereas Himrod is moderately tolerant and Thompson Seedless and Beauty Seedless are tolerant.
Seed Cultivars of Grapes:
Seeded Cultivars:
Anab-e-Shahi is the main stay of grape cultivation in Hyderabad and is also gaining importance in Maharashtra, Karnataka and Gujarat. The berries are large, greenish- yellow, firm, of an excellent keeping quality. The eating quality is average, ripening is uniform and late. The vine is vigorous and gives very high yield on bower system. It does not do so well in North India.
Bhokri or Pachadrakshi is commercial cultivar of Tamil Nadu and Maharashtra. The vine is very vigorous and very high yielding. The fruit quality is mediocre and the keeping quality is poor. The berries are large, rounded and yellowish green. It also does not perform well in North India.
Pandhari Sahebi is shy bearing and slow growing. The berries are whitish, long, and as long as those of Bhokri and with a good keeping quality and an excellent fruit quality. It requires pollination by other varieties.
Cheema Sahebi was selected from the open pollination seedling of “Pandhari Sahebi”. It is mainly grown in Maharashtra. The vine is vigorous and heavy yielder. It is a late ripening variety.
Cardinal is a very early, red table grape and has done well in the arid irrigated regions of North India. The vine is medium in vigour clusters are attractive, medium to large, loose and conical with bright red and spherical berries. The colour changes to reddish black as ripening proceeds. It has a great promise.
Gold is another promising variety of North India especially in arid irrigated tracts of Punjab and Haryana. Vine is medium in vigour. Bunches are loose and medium sized.
Bangalore Blue is a hybrid of the American species V. labrusca and is very successful around Bangalore. It is medium in vigour and yield. The bunches are small and compact, berries dark blackish purple in colour. The ripening is uniform. It is utilized for table as well as juice and wine purposes in Karnataka. It does not suffer from mildew. In North India it does not ripen in time.
Seedless Cultivars:
Pusa Seedless is a seedless variety resembling Thompson Seedless, Sultanina or Oval Kishmish. The berries are small, slightly oval, greenish-yellow and of very good quality. It is early and is very successful in North India. From Maharashtra, clonal selections of Thompson Seedless further resulted in improved type like Tas-A-Ganesh from Sangli, Sonaka from Sholapur.
Perlette is an introduction from California. Its most striking feature is the translucency of the mature fruit. It is the most popular variety of North and Western India. It is one of the earliest maturing cultivar. The vine is vigorous. The bunches are medium large, conical and very compact, and thus need berry thinning. It has good keeping quality.
Delight is a sister seedling of Perlette. It is very early ripening variety and performs well in Punjab and Haryana. It is less vigorous. It has good eating and shipping quality.
Pusa Urvashi is a hybrid (Hur x Beauty Seedless), an early ripening (1st week of June) and basal bearer. Its bunch is loose and medium in size with seedless berries of greenish-yellow colour. It is suitable for table purpose and raisin making.
Pusa Navrang is a cross between Madeleine Angevine and Rubired. It is early ripening (1st week of June), basal bearer variety containing red pigment both in peel and pulp. The bunch is loose, medium in size with round and medium sized berries. It is suitable for making coloured juice and red wine and is also resistant to anthracnose disease.
From IIHR, Bangalore, four hybrids, Arkavati, Arka Kanchan, Arka Shyam and Arka Hans have been developed. All of these hybrids perform well on head system of training.
Grapes are propagated by hard-wood cuttings in India. Cuttings are made from one-season old mature canes after the pruning. The cuttings are 23-46 cm long. The lower cut is immediately below a node and is a square cut. The upper cut is slanting and about 1.5 cm above the apical bud. In North India, the cutting are prepared in February and often planted after keeping them in bundles in moist sand for four to eight weeks for callus formation.
The kniffin, espalier or cane system of pruning is popular in North India. It costs less than the bower system. The vines are trained horizontally along two trellis wires strung on iron supports, one wire being at a height of about one metre and the other at 1.5 metre. The trunk of the vine grows vertically.
One arm about a 0.3 metre is allowed to develop along each wire on either side. Thus each vine has four arms. Long shoots developing into canes are cut back to a length of six to twelve buds, depending upon the variety. Two canes are retained on each arm and are tied along a trellis wire.
Grapevine removes an appreciable quantity of nitrogen from the soil both as wood and fruits. Therefore, to maintain the soil fertility for consistent yield, it is necessary to replenish the nutrients by adding manures and fertilizers.
Propagation of Grapes:
All the commercial grape cultivars are grown over rootstocks in Europe, U.S.A., Australia and Russia due to soil borne problems. In India, all the commercial cultivars are grown on their own roots as self-rooted cuttings.
The grape is best propagated by hard-wood cuttings. The cuttings are made from one year old shoots (canes). The cuttings should be taken from healthy and vigorous vines with well- matured canes. The best cuttings are those which are made from mature vines free from fungal and viral diseases and have a good bearing record. The vines which are poorly nourished and have suffered from drought and frost are not good for the preparation of cuttings.
The medium sized canes with internodes of moderate length are preferred for making cuttings. The outer bark of the canes should be of clear colour i.e., light brown or purple brown, depending upon the variety. There should not be dark blotches, dead streaks or immature areas on the canes. The inner bark of the canes on cut should appear green. Usually the flat or angular canes are not used for making the cuttings. It is observed that cuttings made from the middle part of the cane give higher percentage of rooting.
The cuttings are prepared at the time of pruning in January when the vines are dormant. The cuttings should be prepared promptly after the pruning is done. The length of the cuttings varies from 20 to 25 cm and each cutting should have at least three buds. The general thickness of the cuttings should be 0.75 to 1.25 cm.
In making a cutting, the lower cut should be given immediately below the bud, while the upper cut should be 3-4 cm above the bud in a slanting manner to avoid injury to the top and to hold and orientate the cutting in handling and planting. The finished cuttings should be tied in bundles of 100-200 and should be buried in moist sand or saw dust for about a month for callusing. The callused cuttings start well in the nursery and give a higher percentage of rooting.
Planting of Cutting and after Care:
The cuttings are planted on well-prepared soil in the nursery during February with a spacing 15 cm in rows that are 30 cm apart. After every two rows, a space of about 60 cm is left to facilitate for cultural operations. The cuttings should be planted vertically, keeping only one-third portion above the ground and the remaining two- third portion is buried in the soil.
The cuttings are allowed to remain in the nursery beds for a year after which the rooted cuttings become fit for transplanting in the field. After care of the nursery beds should be regular through frequent watering, hoeing and weeding. The attack of white ants and anthracnose should be checked properly as they cause serious damage. The best time for transplanting the rooted cutting is January-February when the vines are dormant.
Planting Operations for Grapes:
Before planting grapevine, it is essential to prepare land thoroughly by deep ploughing and follow up by tillage so that noxious weeds are killed by it. The land should be levelled thoroughly.
Spacing of vines varies greatly in different grape growing areas. A number of factors influence spacing such as temperature, soil fertility, moisture supply, variety etc. Wide spacing of vines, particularly between the rows makes it easy and more economical. The initial cost of vines, planting stakes and training are directly proportional to the number of vines. Wide spacing between rows overcome crowding between the rows and improves leaf exposure to the light.
In Northern India, grapes are planted according to square system. Vines are generally trained on head system and wire trellis system. In head system, the distance is kept 2.0 x 1.5 metres, which thus accommodates 3300 vines per hectare. In case of kniffin and Y- trellis system, the vines are planted at the distance of 3 x 3 m which accommodates 1100 vines per hectare.
When the vines are trained on Bower system, the planting distance is maintained at 3.0 x 3.0 m which adjusts 1100 vines per hectare. Spacing of vines on Y-trellis should be kept 1.5 x 4m; it will accommodate 1650 vines per hectare. To facilitate proper inter cultivation and management, it is always advisable to keep spacing at the end of rows.
The direction of rows will matter only in the case of Kniffin and Telephone system and not in head or Bower systems. In deciding the direction of rows, it should be taken into consideration the usual direction of the wind. Planting the grapevine rows right angle to the wind need to be avoided, as that, when blowing across is likely to damage the young shoots and the fruit bearing canes, especially in the localities which are affected by wind storms of strong velocity.
In plains of north India, where there is intense heat at the time of ripening of grapes, the rows should preferably run from East to West, so that the ripening bunches are saved from the direct rays of the sun. In localities where the climate is comparatively cool, it would be advisable to set the rows from north to south so that the sunshine is well distributed on both the sides of the vine to facilitate proper maturation and colouring of the fruit.
The planting of vines under north Indian conditions is done in January to first fortnight of February when they are still dormant. The size of the pit should be 1 x 1 x 1 metre dimension. If the soil is light, the size of the pits can be reduced. The refilled pits should be watered a few days before planting the vines. In each pit, add 5 ml of chlorpyriphos 20EC mixed in about 2 kg soil against white ants.
Plants with buds which have sprouted require special care in setting as compared to those that are still dormant. At the time of planting, it would be necessary to train the plants properly. It is usual practice to prune the top three to four buds, keeping only one cane. The straggling roots are also trimmed, broken and damaged roots should also be removed. Vigorous and healthy, one year old rooted cuttings are considered best for planting.
Use of Growth Regulators in Grape Production:
Plant growth regulators are well established as important cultural tools in grape production. They can control specific plant processes that cannot be conveniently or economically controlled by any other means. The growth regulators now can be applied either for promotion or reduction of growth, root initiation, bud or seed dormancy, fruit set, berry size, fruitfulness and total yields of seedless grapes, loosening of clusters, induction of seedless berries in seeded grapes and post-harvest keeping quality of the berries.
The most commonly used auxins for rooting of grapevine cuttings are IBA and IAA. Soaking of the basal ends of the cuttings in IBA 2500 ppm solution for 15 seconds ensures better rooting of the cuttings.
B-9 at 1000 ppm hastened termination of bud rest in grapes. Early bud break in Thompson Seedless grapevines can be achieved by dipping the canes in plastic cylindrical jar containing 1500 ppm paclobutrazol solution. NAA at 750 to 1000 ppm were widely practised in France to delay bud break by 16 to 27 days.
When the flower bud clusters of the male vine were dipped in an aqueous solution of the cytokinin at 1000 ppm three weeks before anthesis, they produced typical hermaphrodite flowers with normal fruit set.
Spraying of SADH at 2000 ppm on Himrod just before anthesis resulted in cent per cent increase in fruit set. GA at 75 ppm 2-3 days after full bloom on Pusa Seedless variety increased bunch length, berry size and weight.
The excessive vegetative growth of vines can be curtailed by spraying the growth retardants like B-9 and phosphon – D at 0.12 and 0.05 per cent, respectively at 10 leaf stage.
Maturity of grapes can be hastened by 6 days by dipping the clusters in ethephon at 500 ppm at the onset of ripening. Ethrel application at 250 ppm two months after set reduced the percentage of green berries to as low as 6.3 and 3.3 in Bangalore Blue and in Muscat respectively as against 30.9 and 25.9 in control. Ethephon at 600 ppm in Perlette at colour break stage advanced ripening.
A pre-bloom spray of GA3 at 15 ppm results in thinning of flowers and cluster elongation in Thompson Seedless and Tas-A-Ganesh cultivars. CCC at 2000 ppm and IBA at 100 ppm were found to be most effective in checking flower and flower bud drop.
Application of GA3 at 50 ppm to Anab-e-Shahi variety 8 days before bloom decreased the bunch weight and the number of berries while one-third of the treated flowers developed seedless berries.
Post-harvest berry drop in Anab-e-Shahi grape is nearly 10 per cent during transit and storage and NAA at 100 ppm was found to be optimum for checking such type of losses. Shattering of berries during storage can be minimised with pre- harvest sprays of cycocel and kinetin at 4000 and 100 ppm concentrations, respectively.
2, 4-D at 1.5 kg/ha is recommended to control weeds in vineyard with precaution not to drift the chemical on to the grapevines.
Maleic hydrazide at 500 ppm sprayed at 5 leaf stage was most effective in increasing the overall fruitfulness of the canes from 22.4 to 59.4 per cent.
CCC treatments significantly increased the number of bunches per vine in Thompson Seedless. Maximum fruit set was recorded with CCC 600 ppm.
To increase the berry size, first application of GA 20 ppm at bloom time for flower thinning and the second application of GA 40 ppm on the same vine at fruit set stage (usually after 10-14 days) proved beneficial. GA 30-50 ppm and Sevin 1000-2000 ppm and ethephon 5-10 ppm at the time of full bloom were found very effective in flower thinning of Perlette grapevine.
Canopy interashading effects cannot only be manipulated by pruning alone yet the use of growth retardants have come to rescue. Paclobutrazol PP 333 (4-chlorophenyl-4, 4-dimethyl- 2- (1, 2, 3-trizol-l-Yl) penton-3-01) inhibits synthesis of plant sterols and specifically GA. PP 333 has been used as pre-bloom sprays and soil application. Pre bloom sprays of paclobutrazol @ 1000, 1500, 2000 ppm in cultivars Roumi Red reduced shoot growth, internodal length but bud fertility was increased. The soil application @ 4 ml per vine was also equally effective. A single application of PP 333 was effective in reducing vegetative growth for a period of two years if the rate of application was greater than 1.1 kg/ ha.
For uniform colour development of Flame Seedless grape, retain 80-90 bunches per vine (75% crop load) immediately after bunch emergence and spray 400 ppm ethephon at colour break stage.
Flowering and Fruiting:
The flowers in grape are borne in clusters. They are perfect, pistillate or staminate. Berry set from pollination, fertilization and seed development. In seedless varieties berry develop by parthenocarpy. Pollination provides stimulus for berry set. This type of parthenocarpy has been reported in Black Corinth cultivars. In other seedless varieties like Perlette, Beauty Seedless, Pusa Seedless, Thompson Seedless and Delight in which fertilization occurs but after sometime embryo aborts (known as stenospermocarpy). Most of the grape varieties are self-pollinated but varieties like Banqui Abyad and Hur having pistillate flowers require cross pollination.
Flowers in grape mostly develop in spring. The parts of flower differentiate in the following order: 5 sepals, 5 petals, and 5 stamens. First the petals are free but later on join along their edges to form the cap or calyptra which covers the flowers bud. There are three main types of flowers. In hermaphrodite or perfect flowers, the stamens are erect with anthers producing functional pollen and pistil is functional.
In pistillate flowers found on female vines of dioecious species of cultivars, the pistil is well developed and functional but stamens are more or less reflexed and pollen is generally sterile. Staminate flowers found on male vines have erect with viable pollen and more or less aborted pistils. Anthesis occurs most frequently between 6 to 9 A.M. and may also occur between 2 to 4 P.M. Anthered dehiscence coincides with the anthesis of flowers.
In certain cultivars like Bhokri and Angur Kalan, it is observed to be completed well before anthesis. In Gulabi cultivar dehiscence started only after anthesis. Pollen tubes have been observed in styles within 3 hours after pollination at 16-27°C. The consequence of fertilization appears 2-3 days after pollination. The berries do not fall from the cluster and are said to have set.
Grape berry grows in three stages. The first and the third stages are the fast and the second one is very slow which is termed as lag phase. The lag phase has been reported due to the presence of higher levels of endogenous growth regulators.
Thinning:
The removal of flower clusters before flowering or parts of such clusters after fruit set is called thinning. Like pruning thinning consists removal of living parts and it concentrates the activities of the vine into the left parts. In other aspects, however, thinning has the opposite effect of pruning it strengthens the vine by limiting the crop without reducing the leaf area.
Thus thinning offers for greater possibilities for improvement of fruit quality than does pruning. In winter, when pruning is done the next year’s crops can be estimated by experience or on the basis of fruitfulness of the buds. After the clusters appear, however, the potential crop can be seen hence pruning accompanied by thinning permits a better balance of capacity and crop than does pruning alone.
Thinning makes it possible to grow as much crop as the vines can bear without sacrificing quality with thinning, it may actually be possible to increase bearing capacity, since vines that are to be thinned can be pruned longer to produce a greater, leaf surface, which is not possible when crop load is to be determined by pruning alone.
Fruits of thinned vine are less prone to decay. Properly thinned fruit is less costly to pick because clusters are more uniformly coloured and less time is required in selecting the ripe cluster. Different grape varieties do not set the fruit equally well with normal thinning. Some tend to set straggly clusters, others nearly perfect clusters while some like Perlette over compact clusters. To obtain maximum improvement in fruit quality in these variations in set different methods of thinning have been recommended.
(i) Flower Cluster Thinning:
It is done between leafing out and blooming. Flower cluster thinning is practised in cultivars which tend to set straggly clusters. It reduces the number of clusters without reducing the number of leaves. With an increase in leaf cluster ratio, the flowers on the retained clusters are better supplied with food materials. The flower parts develop more perfectly, fruit set will be more and there will be a large percentage of normal berries. This method is generally applied to grape cultivars like Cardinal, Muscat of Alexandria. Flower cluster thinning can also be practised to rejuvenate weakened vines.
(ii) Flower Thinning:
Flowers thinning by the use of mechanical means like plastic brushes or removal of some of the laterals by hand before the fruit set needs to be practised in grape cultivars like Perlette which tend to set heavily. In this variety, the cluster become over compact and are susceptible to berry rot at the time of ripening and also a high percentage of berries remains under sized. In Perlette, Gibberellin (30-50 ppm), Sevin (1000-2000 ppm), ethephon (5-10 ppm) and use of plastic brush at the time of full bloom have found to be very effective in flower thinning.
(iii) Cluster Thinning:
It consists of removal of entire clusters after the fruit set. This method has no effect on fruit set or cluster length. It is essentially a grading and sorting of clusters at an early stage. Misshapen, small sized and over-sized clusters are removed. This provides more favourable conditions of growth for the remaining clusters, giving larger berries. It is employed in cultivars like Empror on heavy soils. Cluster thinning is easiest and best means of reducing crop on overload vines of highly productive wine grape or raisin grape vineyards.
Cluster thinning, however, is a time consuming and costly affair. In case of Perlette, thinning of bunches is necessary so that the remaining bunches develops properly. It is recommended that not more than 100 bunches be left on each vine (trained on bower), planted at a distance of 3 m x 3 m. The thinning should be done soon after the berry set and all small and under developed clusters should be removed.
(iv) Berry Thinning:
Berry thinning consists of removing parts of clusters or individual berries after fruit set. The rachis of the cluster can be cut back to retain the derived number of berries. In addition to its removal of some of the laterals it provides more space for berry development and prevents compactness of the clusters.
Berry thinning should be done soon after fruit set especially in seeded cultivars. The removal of individual berries is very time consuming and uneconomic. Berry thinning is not as effective in increasing the berry size in seedless cultivars. It is, however, very important in preventing over-compactness of the clusters when berry size is either increased by girdling or use of growth regulators.
Quality Improvement in Grapes:
To get optimum yield and quality of grapes the following package of treatments should be adopted:
(i) Thin flower buds one week before flowering by leaving 100-120 flower buds per panicle.
(ii) When berry size is 4 mm, girdle the vine by removing a 4 mm wide ring of bark from the main stem and dip the clusters in 40 ppm GA3. While girdling, there should be no injury to the wood and no piece of bark should remain attached with the wood.
(iii) One week after the first GA3 + treatment, give a second dipping in 40 ppm GA3.
(iv) The field should have sufficient moisture during girdling and atleast 3 weeks after that.
(v) Harvest the crop when attained the requisite TSS content.
Two foliar sprays of potassium sulphate @ 1.5 per cent, first one week after fruit set and second at colour break stage, improve the quality and colour of Perlette grapes.
Harvesting and Fruit Handling of Grapes:
Grape is harvested when it is fully ripe as it is a non-climacteric fruit. It is said to be in ripe stage when it attains characteristic colour, flavour and aroma which constitute the quality of grapes. After harvesting the grape, its quality remains same without subsequent change in colour. Also, over-ripening of grapes on the vine, do not fetch premium in the market and pose serious problems in its transit and storage. Therefore, harvesting of grapes at the optimum stage is of prime importance.
Sugar-acid ratio might be a more reliable indicator for grape harvesting. However, the harvest of varieties with lower acid content (0.40 – 0.75%) could be based on TSS content alone, while for the varieties with high acid (more than 0.95%), the criterion should be acidity alone. The varieties with medium acid content (0.75 – 0.95%) should be harvested based on the TSS/acid ratio. The ratio must be higher for low acid varieties than for high acid varieties to maintain a given level of acceptability.
Berries at the apical end of the bunch ripe faster while those at the distal end ripe slow. Only 38-50% berries in a bunch can match the quality standards of the berries in the middle of the bunch.
pH of the juice is another criterion used for predicting maturity. pH measurement is an expression of the free or active acidity at any stage in the development and represents the state of balance of the chemical constituents at that time. During growth, the pH of grapes constantly undergoes change, starting with low in the immature grape and reaching a high value in the overripe stage. It would appear reasonable, therefore, to draw the conclusion that pH can serve as an indicator of maturity. In Thompson Seedless, a pH of 3.7 may be suitable for table grapes if drying and rotting have not set in. General recommended pH for Thompson Seedless is 3.45 – 3.50 for harvest.
Harvesting:
Grape should not be harvested until they are fully ripe. There are many indicators to the proper stage of ripeness of grapes for picking but the taste is the most valuable indication of the ripeness of the bunch. For this purpose, the greenest barriers, which are always near the tips, should be tasted. If they are good to eat, the entire bunch is ripe for picking. Fully ripe bunches should be picked for local consumption while for distant markets, bunches should be picked when still hard ripe so that they do not spoil during transit.
Ripe grape bunches should be clipped with scissors without injuring the berries. During handling, the natural bloom on berries must not be rubbed off. Harvesting should be done during the coolest period of the day. Bunches should not be exposed directly to the sun. Trimming, grading and packaging should be done in shade.
Undesirable berries viz. unripe, over-ripe, small, misshapen, sun-burnt, decayed, soft and bruised should be trimmed. Bunches should be graded according to the fruit quality, maturity and size and different grades should be packed in different containers. For nearby markets, mulberry or bamboo baskets can be used, whereas for distant market, wooden boxes of 2-4 kg capacity or Corrugated Fibre Board (CFB) cartons should be used.
Being a perishable fruit, it cannot withstand high temperature and low humidity prevailing at the time of harvesting which causes 25-30 per cent losses through spoilage and cut down the already meagre storage life of grapes under ambient conditions. Thus after harvesting it has limited possibility for transport to the distant markets in a good condition which further restricts its marketability. It is, therefore, desirable to store the sufficient quantity of grapes at harvesting time to spread its marketing over a longer period.
In Perlette grapes, ethephon at 400 ppm if applied at colour break stage-advances fruit maturity, increases total soluble solids and reduce fruit acidity.
Storage:
Factors in storage environment that effect grape quality are temperature, atmospheric humidity, air movement and fumigation with sulphur dioxide. Recommended temperature for cold storage of grapes is 0°C to 2°C and relative humidity between 85-90 per cent. These grapes can be kept upto 40 days. Shelf life of grapes can further be improved in storage by removing field heat by forcing the air through the boxes at 2°C less than cold storage temperature.
Good refrigeration is needed in storage, because Botrytis decay growth at 2°C is double than that at 0°C. In controlled atmospheric storage, grapes can be stored for 2 — 3 months at 1°C and 95% relative humidity with oxygen and carbon dioxide concentrations at 10 and 3 per cent, respectively.
Flame Seedless grapes harvested at optimum maturity with firm berries having light purple colour and packed in ventilated CFB boxes of 4 kg capacity lined with polythene film containing one sheet of grape guard can be stored at 0 – 2°C and 90 – 95 per cent RH with acceptable quality for 45 days. Grapes packed in LDPE bags with single sheet of SO2 generating pad and kept in CFB boxes can be stored for 30 days at 0-2°C temp, and 90-95 per cent RH with acceptable quality.
Processing:
Processing technology of grape vinegar from Perlette at 5 L scale has been standardized at PAU, Ludhiana. This will provide an alternate use of grapes cv. Perlette. It is a fruit based natural vinegar with properties of grapes and vinegar blended together. Grape vinegar has shelf life of two years.
Diseases and Pests of Grapes:
Grapes are susceptible to a number of fungal diseases. Summer rain accompanied by high temperature spread the diseases. The most serious disease is the powdery mildew caused by the fungus Uncinula necator. It develops in a hot sultry weather but not during actual rain.
White powdery patches appear on both surface of leaves, on shoots and flowers. It hinders fruit set, the young berries fall off and the vines may show wilting. Ripe berries are not affected. It is not a serious problem in North India but in Tamil Nadu and Maharashtra it is active in October. It can be controlled by dusting finely powdered wettable sulphur (0.2%) or 0.1% Karathane spray at 5 to 7 days interval during infestation.
Downy mildew caused by the fungus Plasmopara viticola develops in cool humid weather. It is more serious in peninsular India. A greenish yellow spot appears on the upper surface of the leaf. This spot turns brown and dries up. Later white mouldy patches develop below these spots on the lower surface of the leaf.
It also attacks the bunches. The berries wither, turn brown and then shrivel and shatter easily from the bunch. Spraying of Bordeaux mixture repeatedly at 6-7 days interval is still the most widely adopted control measure.
Anthracnose caused by the fungus Elsinoe viticola, develops in wet weather at lower temperature and is the most destructive disease especially in North India. Dark brown spots with darker margins are formed on the leaves around midrib and main veins. However, the lesions on canes are elongated sunken, dark brown with dark purple raised margins.
Red spots with grey centre develop on berries. The vine should be sprayed immediately with 0.2% copper oxychloride. Spraying the vineyard at leaf emergence with 0.2% Benlate or Bavistin and repeated after one month, is also effective.
The most important insect pest of grapes is the Flee beetle, Scelodonta strigicollis which causes damage in spring by cutting holes in the leaves and also feeds on sprouting buds and emerging shoots. Spraying with 500 ml Malathion (50 EC) or 1.5 kg Carbaryl (50 WP) in 500 litres of water controls this pest.
Chaffer beetle (Adoratus spp) feeds voraciously on leaves during night time leaving only the veins and hides during day time. Dusting of Lindane at interval of 10 days during rainy seasons is effective. Wasps, Honey bees and birds also cause considerable damage to ripening berries.