Plum is a minor fruit crop of Punjab which can be planted as filler or in solid blocks. It is highly productive with medium sized,sub-acidic fruits. Plums are rich in sugars and vitamin-A. Fruits are used either as fresh fruits or processed into squash and jam.
Climate and Soil
Plum is grown under sub-tropical conditions both in plains and in sub mountain areas of the Punjab. Varieties with chilling requirement below 300 hours can be grown successfully. Areas receiving 100-125 cm rainfall well distributed throughout the growing season are suitable for plum cultivation. Plum orchards are prone to damage by high wind velocity and must be protected by planting wind-break trees.It can be grown successfully in deep, sandy loam soils with good drainage which are free from alkalinity and salinity conditions.Availability of ample good quality irrigation water is of primary importance while selecting a site for plum plantation. Plum trees will fail to produce commercially acceptable crop if they suffer from water deficit.
Satluj Purple (1990) : It is a self unfruitful variety and requires Kala Amritsari as pollinizer. Pollinizer should be planted as an alternate plant in alternate rows for maximum yield. Satluj Purpleand Kala Amritsari plants should be planted in the ratio 85:25 in an acre. Trees are medium in vigor with upright growth habit. The fruit is medium large with average weight of 25-30g, roundish, turns into crimson color on ripening. Fruits are thick skinned with yellow orange firm flesh. It is sweet in taste having 13-14% TSS and 0.6-0.7% acidity and is suitable for table purpose. It is an early variety ripening in the first week of May with average yield of 40 kg per tree.
Kala Amritsari (1979) : It is self fruitful, high yielding indigenous variety with vigorous tree. Fruits are medium sized, round oblate depressed at both ends, on ripening turn dark purple. Flesh is yellowish with moderately juicy pulp. Fruits are somewhat acidic with 15% TSS and 1.2 per cent acidity. It ripens in the second week of May. Average yield is 45 kg /tree. Fruits are excellent for jam making.
Kala Amritsari is propagated by hard wood cuttings while Satluj Purple by simultaneous grafting and rooting of rootstock cuttings.The time of preparation of cuttings and grafting is from end of December to end of January. Hardwood cuttings of Kala Amritsari should be 15-20 cm in length with 4-5 buds on them and should be of pencil thickness . To increase the rooting success their basal parts (4-5cm) are dipped in 100ppm IBA solution for 24 hours. For making this solution, dissolve 100 mg IBA in 10-15 ml of alcohol and make up the volume to one liter.
Satluj Purple is multiplied through stenting technique i.e.simultaneous grafting and rooting of rootstock cuttings. The cuttings of Kabul Green Gaze are used as rootstock. Rootstock cuttings about 20 cm in length are tongue grafted with scion wood in the first fortnight of January. The basal parts of the grafts are given 24 hours soaking treatment with 100 ppm IBA solution. The cuttings/grafts are transplanted in well prepared nursery plots at a distance of15-20 cm in rows spaced 30 cm apart. The plants from the cutting/grafts are available for planting after one year in the month of January.
Plum is planted either in solid blocks at 6mx6m distance or asa filler trees in mango,litchi and pear orchards during the first fortnight of January. The plants of Kala Amritsari are also transplanted in the orchard of Satluj Purple as pollinizer in the ratio of 25:85 plants/acre. Alternate plants of Kala Amritsari are planted in the every second row of Satluj Purple for effective pollination and improving fruit set in the orchard.
High density planting : Satluj Purple plum trees can also be planted at 6x1.5 m distance with modified leader system and summer pinching (10-15 cm). This practice ensures high yield of better quality fruits. Training.
Training and Pruning
Training : Plum trees are trained according to modified leader system. The training is completed in 3 years from planting. One year old healthy plants about one meter in height are transplanted in the first fortnight of January. The plant is headed back at immature terminal part at planting time. If the branches are present on the stem these are prunned to short stubs. The plants sprout in February and produce numerous shoots during spring and summer months and continue growing until about the beginning of October. During the first dormancy, select 4-5 branches around the central axis spaced at 15-20 cm vertically one above the other. The remaining branches present on the central axis should be removed. At this stage the central terminal branch is called the leader. The lowest branch on the stem should be about 45 cm from the ground. During second year, plant grows in height, produces secondary branches on the selected primary limbs and new branches above the first year extension. In the third year, the tree grows and produces many new branches on primary as well as on the secondary limbs. Out of these wide angled, well-spaced branches are selected and rest are removed. In the end of the year when the plant has developed good frame-work, central leader is headed back close to an outward growing lateral. In this way the modified leader trained plant is ready for bearing fruit.
Pruning : Plum trees bear on one year old growth as well as on short spurs depending upon the variety. Generally, light annual pruning should be done in January. It consists of the removal of thin and crowding twigs and branches within the tree. Criss- crossed and lengthy branches or out of place, dried and diseased branches should be thinned out to admit sunlight in the tree center for the development of better color of fruits. Besides, water sprouts or suckers arising from the crown part of the tree should also be cut regularly. After every 4 or 5 years of fruiting, heavy pruning of the trees is done by heading back the lengthy branches about half of their length . The cuts thicker than 4-5 cm should be covered with Bordeaux paste or Bordeaux paint.
Manures and Fertilizers
Manures and fertilizers to the plum trees are applied according to their age. Age Farm yard Dose per tree (g) (years) manure Urea Super Muriate of((kg) phosphate Potash1-2 6-12 60-120 95-190 60-1203-4 18-24 180-240 285-380 180-2405-6 30-36 300-360 475-570 300-3606& above 36 360 570 36095 96 Apply farm yard manure, super phosphate and muriate of potash in December. Split the N fertilizer in two halves. Apply half ofN fertilizer in spring before flowering and second half one month later after fruit set.
Plum trees growing on light textured soils generally show zinc deficiency symptoms on the current season growth in the summer months. The affected leaves on the terminal parts of branches are narrow, small with interveinal chlorosis. On the growing tips, the affected leaves appear in whorls i.e.rossette form. If the deficiency persists, it may cause die back of the twigs and the fruits become hard and undersized. Zinc deficiency can be corrected by foliar spray (0.6% Zinc sulphate solution) containing 3 kg zinc sulphate and 1.5 kg unslaked lime in 500 liters of water as and when the deficiency symptoms are observed on plants.
The young plum plants up to the age of 3-4 years need irrigation at 4-5 days interval during summer months starting from April to June. Being deciduous, the plums do not require frequent irrigation during winter. Apply irrigation only when the drought period is prolonged. The bearing trees should be given regular irrigation from fruit set to maturity. In summer, irrigation should be given at an interval of 4-5 days.
Weeds should be checked by manual ploughing in the soil.
Control of pre harvest fruit drop
Two sprays of NAA 10 ppm in 2nd and 4th week of April or one spray of Ethrel 100 ppm in 4th week of March (after pit hardening)reduced the pre-harvest fruit drop in plum cv. Satluj Purple.
Caution : i. There should not be any water stress in the orchard at the time of spray of growth regulators.ii. Ethrel 100 ppm should be sprayed just after pit hardening and neither before nor later than this. Otherwise, it may increase fruit drop.iii. As the fruit growth is rapid during April, trees should be irrigated frequently.
Fruit Maturity and Harvesting
The maturity of plum fruits is indicated when these have attained normal size and color. The peak season for plum harvest in Punjab starts from first week of May. The first sign of fruit maturity is the change of green color to purple, red or yellow according to the variety. For local consumption fruit should be picked at ripe but firm stage. For distant market, fruits are picked when these have developed 50% color on the skin and should be firm.
Plum fruits are harvested with stem intact avoiding any skin injury. Fruits being perishable in nature should be handled with care.The basket used for picking should be padded with soft dry grass at the bottom and on the sides. Immediately after harvest, transfer the fruit to some shady area under the trees / shed. For local market,fruit should be picked in the early hours of the day and immediately shifted to the shed / tent for sorting, grading and packaging. For distant market the fruits are picked in the evening hours and kept in the orchard shed to cool them overnight for sorting, grading and packaging.
The fruits which are over ripe, soft, bruised or immature should be discarded. Fruits are graded according to their size, color and appearance. Different grades of fruits are packed in separate boxes and labeled. Three standard sizes recommended under “Ag-Mark”system of grading of plum along with the box size are as follows:Grade Fruit size Inner size Number of Number of(diameter in cm) of box (cm) layers fruits/layer Special 4.2 & above 36x16x16 3 28-32 Grade-I 3.6-4.2 -do- 4 38-42 Grade-II Below 3.6 -do- 4 50-56 In general, the fruits should be packed in 5 kg wooden boxes instead of bamboo baskets. To prevent the fruits from injury, interior of wooden box should be lined with newspaper sheets on all sides and paper strips as padding at the bottom. The fruits are placed in layers. After each layer make a partition of paper strips over lined with newspaper sheet. Top layer of the fruit is covered with a cushion of paper strips and newspaper sheet and finally the lid of the box is nailed.Plum is a perishable fruit and its shelf life is short. Low temperature storage prolongs the effective life of fruit. For best results fruit should be picked at the correct maturity and placed immediately in commercial cold stores where temperature is 00-3'C with relative humidity 85-90%. The fruit remains in good condition for 25 days.To facilitate better marketing of plum, refrigerated vans are desirable for transportation.
8Storage : The Satluj Purple plum fruits, harvested at color break stage, followed by post-harvest treatment of calcium nitrate(2%) solution for five minutes, can be stored for four weeks in cold storage (0-1'C and 90-95% RH) with post storage shelf life of 2 days at ambient temperature.Non alcoholic naturally carbonated beverage can be prepared from fruits of Satluj Purple and Kala Amritsari plum at small and large scale. It has three months shelf life and retains its original nutrients.