Everything you need to know about growing citrus plant! Learn about: 1. Botany of Citrus Plant 2. Origin of Citrus 3. Soil and Climate 4. Orchard Cultural Practices 5. Propagation and Root-Stocks 6. Planting Operations 7. Flowering and Fruiting 8. Training and Pruning 9. Harvesting and Marketing 10. Varieties.
Botany of Citrus Plant:
Mandarin and sweet oranges are placed taxonomically in the division Embryophyta; subdivision Angiospermae; class Dicotyledoneae; order Geraniale; suborder Geranianeae; family Rutaceae; sub-family Aurantioedae; tribe Citrae; sub-tube Citrinae, genus Citrus.
Swingle recognized only 16 species under the genus Citrus whereas Tanaka described as many as 144 species. Swingle divided the genus Citrus into two subgenera viz. Eucitrus having 10 species and Papeda having 6 species. Swingle’s treatment was not comprehensive and he considered most species to be of hybrid origin and rejected which were not found to occur in nature in wild form. Tanaka divided the genus Citrus into two subgenera viz, Archicitrus having 98 species and Metacitrus with 46 species. His treatment although considered as more comprehensive and detailed, contains excessive number of species, some of them being of doubtful validity.
A good number of citrus species have been exploited commercially some for direct fruit production and some as rootstock. In addition, quite a large number of intergeneric and interspecific hybrids have been developed. Citranges (trifoliate orange x sweet orange), citrumelos (trifoliate orange x grapefruit), citradias (trifoliate orange x sour orange), citrumuats (trifoliate orange x kumquat), Citrangedin (citrange x calamondin), citrandarin (trifoliate orange x mandarin), citremon (trifoliate orange x lemon), limquats (kumquat x West Indian lime) are the intergeneric hybrids, which were developed in hybridization work.
In the interspecific hybridization programme, a few other groups like limonimes (lemon x lime), tangors (mandarin x sweet orange), tangelos (mandarin x grapefruit), Lemorinage (lemon sweet orange), lemandarin (lemon x mandarin) have been developed.
Origin of Citrus:
Citrus consists of a group of fruits belonging to the family Rutaceae, to which belong the bael (Aegle marmelos), wood-apple (Feronia limonia) and the ornamental shrub Kamini (Murraya paniculata) with sweet smelling flowers. The special feature of citrus fruits is the presence of juice sacs in them.
The citrus fruits also contain vitamin P, which keeps the small blood vessel in our bodies in a healthy condition and helps in the assimilation of vitamin C. Tablets of vitamin C prescribed by the physicians are, therefore, not as effective in relieving the deficiency of this vitamin as much as fresh citrus fruits.
It is interesting to note that the richest sources of vitamin C, the Barbados cherry and the aonla (Emblica officinalis) also belong to families which are botanically very closely related to the family of the citrus fruits. The only other fruit rich in vitamin C is guava, which does not belong to this group.
There are many kinds of citrus fruits found in the world. These breed with each other in nature freely and new types are coming up from time to time. In India a rich array of these types is found growing semi-wild. Most of these are indigenous to India and have originated in the Assam area. They grow wild in the submontane areas. The most important among these is the rough lemon, “Jambhiri”, “Jamburi”, “Khatti” or “Jatti Khatti” (Citrus jambhiri). It is the commonest root-stock in India.
The other indigenous species are Satkara (C. macroptera var. assamensis), Citrus indica and Adajamir found in Assam, gajanimma (C. pennivesiculata) and Kichili (C. maderaspatana) found in South India and amilbed (C. megaloxycarpa) and hill lemon, galgal, Biharee nimbu or paharee nimbu (C. pseudolimon) found at the foot of the Himalayas.
About amilbed, Emperor Babar has said that it is so sour that it would dissolve a needle thrust in its pulp. This, of course, is great exaggeration. Two other species found growing semi-wild are pummelo and citron, but these are not indigenous to India. The pummelo has the largest citrus fruits and produces the largest trees among the citrus group in heavy rainfall areas around Sikkim and Nepal. It seems to have been introduced at a very early age.
None of the above species is cultivated in India as a table fruit except the Kichili. The important commercial citrus fruits grown in India are definitely not indigenous to this country. The most important is the mandarin orange, santra, sangtra, or Kamla orange (Citrus reticulata). This is a loose-skinned orange and is often erroneously called orange which, in the English language, denotes the tight skinned orange (C. sinensis).
The sangtra, as is suggested by its name mandarin, originated in South China. It is possible that it originated further south in Indo-China. It came to India in the beginning of the Christian era. It was probably brought from the east by the Shan people of China from Yunnan to Assam. In Babar’s time it had not spread west of Bengal. However, at present it is the most important citrus fruit of India cultivated all over the country.
An ornamental citrus plant found in India is the Calamondin, China orange or Hazara (C. madurensis or C. mitis). It bears small ornamental fruits, which continue to hang on the tree for months. It is often raised in large pots. It is the same fruit as the Calamency orange of the Philippines which is used for flavouring tea in that country.
The era of growing citrus as a backyard plant has given rise to commercial plantations. The area under citrus has been increasing in spite of the threat of citrus decline and citrus canker. In India, citrus occupies an area of 618.5 million ha out of the total area of 4010.2 million ha under all fruits.
It will be noticed that little citrus is grown in the Tamil Nadu, Bengal, Assam and Gujarat even though citrus cultivation in Assam is successful on the hills. In area of high rainfall, the plants fall a prey to many diseases due to high humidity.
India ranks second in the production of lime/lemon fruits in the world. It occupies third position after mango and banana in the production of fruits in India.
Citrus fruits rank second in total area with 6.18 lakh ha with production of 47.89 lakh tonnes, which is 11.1% of total fruit production. Limes, lemons, sweet orange and mandarin cover bulk of the area under this group of fruit. Citrus fruits are grown mainly in Maharashtra, Andhra Pradesh, Punjab, Karnataka and north-eastern region.
The other fruits grown commercially are Kichili (C. maderaspatana) in Andhra Pradesh, sweet lime (C. limettioides) in the Punjab and Tamil Nadu and pummelos (C. grandis) scattered all over the country.
Soil and Climate Required for Growing Citrus:
The fact that citrus grows in all parts of a vast country like India clearly shows that it can thrive in a wide range of soil and climatic-conditions. It grows in almost any soil. In the Nagpur area mandarins grow on heavy black soils, and in Assam they grow on sandy and gravelly hill-slopes. In Andhra Pradesh, the red laterite soils used for citrus are often very heavy. The alluvial soils of the Punjab range from light to heavy.
The heavy soils of Nagpur are under- laid with a murrum layers, which provides a good drainage. The type of soil seems to be immaterial so long as sub-soil drainage is good. Under poor drainage, the soil becomes water-logged around the roots during heavy rains in the monsoon season even though the water-table may not be high. The failure of sweet orange in several places in the Punjab and U.P seems to be due to this factor. The failure of citrus in many garden colonies in the Punjab is undoubtedly due to poorly-drained soils. Where the water-table is high and it also fluctuates, citrus has no chance.
On the other hand, citrus does exceedingly well in sandy soils which are well-drained, provided sufficient nutrients are supplied to the plant. Such is the case in Florida in the U.S.A, where the soil is coarse sand, the water-table is at about 1.25 metres and fertilizers are applied almost every month. A moderate amount of lime in clayey soils makes them more friable and is good for citrus, but excess lime as found in the marl lands of the Deccan peninsula is poor in nutrients and toxic to oranges.
The climatic range tolerated by citrus is remarkable. It grows not only in the scorching dry plains of North India, but also on the cool hill-slopes of Sikkim and Darjeeling and in the tropical conditions of Tamil Nadu. The mandarin shows a wider range of adaptability with regard to rainfall and can tolerate cold weather better. It grows successfully from the Himalayan climate of Sikkim to warm dry places like Nagpur. In colder areas the fruit is puffy but its colour develops better. In Nagpur the fruit remains pale orange in colour. The rainfall in mandarin areas is around 75 cm in the plains and up to 250 cm on hill-slopes.
In Coorg and adjoining areas where the mandarin grows at altitudes ranging from 700 to 1000 metre, the temperature ranges from 40°F to 90°F, but in Nagpur the summer temperature goes above 105°F. However, in the hot summer temperature the fruit gets sun-burnt. Mandarins, like lemons, ripen well during comparatively cool summers. Extreme cold and extreme heat are not desirable.
Mandarins do best in an equable tropical climate with a cool summer. They thrive in the hilly areas of Assam, Darjeeling, Coorg, Wynad and the lower Nilgiri Hills without irrigation and in Nagpur in Central India with irrigation. They do not like the humid warm plains of South India and the hot plains of North India. The distribution of rainfall is also important. Heavy rain at the time of flowering after a long dry spell can cause excessive vegetative growth and poor flowering.
It has been observed that the sweet orange can stand a more humid climate than mandarin, but both are sweeter in a dry climate if proper irrigation is available. In North India, where the minimum temperature in winter generally ranges from 35°F to 40°F, the trees not only get a proper rest period for flowering in spring, but the fruit also develops a good colour. The Mosambi orange remains light yellow coloured in Maharashtra, but when grown in North India it develops a bright reddish orange colour. In warm winter the red pigment in the pulp of blood oranges also does not develop. When a hedge of Sesbania aegyptiaca is grown on the south side of the trees to protect them from the heat of the sun, the blood colour improves considerably. The blood pigment can also be developed by storing the fruits for six weeks after harvest at temperatures from 32°F to 39°F.
The sweet orange prefers a more sub-tropical climate. It requires a warmer summer for ripening. However, it can be grown even in the plains of South India where winter is very mild. The conditions prior to flowering are more important. Under North Indian conditions the different citrus species produce from three to five flushes of vegetative growth. Shoot-growth takes place between 56.6°F and 75°F and root growth between 61°F and 82°F. Flower buds differentiate from January to March and the individual shoots show alternate bearing. The earlier vegetative flushes of the previous season generally are more productive.
Pummelo can stand more rainfall and does not thrive in dry regions. It thrives in submontane areas. Grapefruit on the other hand thrives best in the hot plains of North India. Here it makes better growth and develops better quality than any other citrus species. Sour lime grows in high rainfall as well as in drier climate.
Citrus is essentially a sub-tropical fruit. It is also a tender plant which is not able to survive in the truly wild form in jungles anywhere. Its mere survival in the plains of North India is a heat. Here it faces scorching dry heat and lack of moisture in May-June. Immediately afterwards it is exposed to high humidity and consequent diseases and pests and water-logging of soil in the monsoons. In winter it has to face frosty nights. Under these conditions, its cultivation requires special care.
In North India citrus generally flowers in spring (March) and the crop matures in August-September in case of sweet lime (C. limettiodes) and from November to February in others. However, as we travel towards South, the winter is too mild and regular flowering does not take place at one fixed time. In South India, the seasons are less well-defined and longer. Flowering takes place several times in a year.
Spring flowering takes place earlier in December to March. A second flowering takes place from September to November and a small third one from June to September. The crops from these flowers mature in November-March, June-November and March-June, respectively. In Central and Western India, the spring flowering in February called the ambe bahar, gives the main crop in November-December, the mrig bahar in July gives the second crop in March-May and hast bahar in September-October gives a small third crop in July-August.
The fruit of mrig bahar comes to the market when the demand is good. Its fruits being too raw and acidic during the rainy months also escape the attack of the fruit sucking moth. It is also good for areas where there is scarcity of water in May-June, when the trees are given rest.
In Central India, in order to get one abundant crop instead of three poor ones, the trees are given a bahar treatment. Irrigation is withheld for two months before flowering. If the leaves of the trees do not wilt, as happens in heavy soils, the soil around the trees is removed up to a depth of 12 cm and the small roots are removed. After ten days, the soil is mixed with manure and put back. A light irrigation is given and is followed by a medium irrigation, after about seven days. Normal irrigation is given after another ten days.
This ensures that the tree does not produce a sudden and heavy vegetative flush and encourages profuse flowering. The September-October flowering is not given this treatment since it does not respond to it well due to rains and also does not give a good crop. This practice is not followed in North India where it is not needed, and in South India, where its immediate effect is not to increase the crop, but to decrease the vigour of the trees in the long run. Bahar treatment in South India is also made difficult due to frequent rains, which interfere with the rest period.
Orchard Cultural Practices for Growing Citrus Plant:
In India, citrus is generally planted at a density of 250 to 350 plants/ha. depending upon the variety, the rootstock and the agro-climatic conditions. In Karnataka, Coorg mandarin on trifoliate orange and Rangpur lime rootstock is planted with a density of 400 and 275 plants/ha. respectively.
With the wider spacing of the new orchards, inter-cropping and cover-cropping have become imperative. In some places, coffee is grown as an inter-crop. Vegetables are often grown as inter-crops. In the past, growing of the leguminous crop of berseem (Egyptain clover) was recommended, since it adds nitrogen to the soil. It is being abandoned now, since it requires frequent irrigation in winter, which is harmful to the citrus trees. In the Punjab, growing of cotton as an inter-crop in young citrus orchards was recommended. Now it has been abandoned due to adverse effect on kinnow plants and harbour of pests and disease.
Unlike the apple, which can grow well under sod cultivation, citrus cannot stand the growth of weeds. However, in hilly areas like Assam the old plantations have never received any cultivation. In the plains the fields are cultivated three or four times a year. Generally the cultivation is too deep. The feeding roots of the citrus plants are within 15 cm of the surface of the soil. So the cultivation should be superficial. If there are no weeds, the absence of cultivation would be better than deep cultivation.
Irrigation of citrus, especially in summer, is important. The young plants are irrigated by the basin or ring system and the adult plantations generally by flooding. However, flooding requires too much water and furrow irrigation is better. No irrigation is required during the rainy months. The critical period for irrigation is summer. Frequent light irrigation during this period is more useful, since it lowers soil temperature and raises humidity. In some places up to 20 annual irrigations are recommended. In the hilly areas, there are no facilities for the irrigation of mandarins. Here the yearly rainfall is generally around 250 cm, but in summer the trees suffer from serious shortage of water.
Citrus requires heavy manuring and in India it does not receive the quantity of fertilizer it needs. Of the major nutrients, nitrogen is definitely required to be replenished, even though some old plantations were never manured. The general feeling is that FYM is better than chemical nitrogenous fertilizers. This may be due to the presence of other nutrients besides nitrogen in it. In North West part of India (Punjab, Rajasthan) a full bearing citrus plant should be given 60 kg of FYM, 2.5 kg ammonium sulphate, 2.5 kg super phosphate and 1.5 kg sulphate of potash.
Propagation and Root-Stocks of Citrus:
Mandarins are propagated as seedlings in Coorg and Assam, where they are grown in conditions of heavy rain. The seedling trees come to bearing late, but live longer. One hundred-year-old healthy seedlings of mandarins can often be seen. The seedlings are thornier as compared to budded plants. Sour limes are also propagated as seedlings very often. The delay in the age of bearing in this case is very little. The Sathgudi oranges in the Rayalaseema area are often raised as seedlings, which give more disease resistant and longer-lived trees.
Sweet lime is generally propagated by layering or from hardwood cuttings. September is the best time for planting cuttings and the results are improved by treatment with Seradix A or IBA500 ppm. In Assam air-layering of mandarin, sweet lime and Mosambi gives success varying from 90 to 100 per cent. The commonest method of propagation, however, is T-budding which is a successful method all over the world. The seeds of citrus root-stocks lose their ability to germinate very soon and should be sown within two weeks from the extraction of the fruit.
Seeds are ready for germination even before the fruit has changed its colour. Seeds are generally extracted and sown in August-September. In Central and South India, they are also sown in May-June. In North India if sowing is delayed, the cold weather sets in and the germination is poor. However, raising the seedlings under alkathene cover gives a high (85%) seed germination with fast growth of seedling. The plants become budable in a year’s time. Precaution for “damping off” is to be taken.
Storage of seeds till spring reduces germination, which can be tested by the tetrazolium test. They are sown in raised seed-beds containing leaf-mould, 2.5 cm apart in rows spaced 77 cm apart. They start germination within three weeks and are transplanted later at wider spacing. In the common root-stocks of citrus, several seedlings arise from each seed. One of these is the sexual seedling and it is generally weak. It should be discarded. All weak and overly vigorous seedlings are uprooted.
Citrus plants being evergreen are generally transplanted with a ball of earth. However, under moist tropical conditions, they can be dug out with bare roots on a cool cloudy day. They are planted finally in beds. All side-shoots arising within 30 cm of the ground are rubbed off to get a straight stem. The seedlings are ready for budding in about a year. The removal of wood from the bud in case of angular scions often damages the bud, and budding along with the chip of wood gives good results. In mandarin, the removal of wood seems to decrease the percentage of success, but the buddings make better growth. In sour lime, the bud-take is more with the wood.
Budding is generally done either in spring or in August- September in North India. In Western India, budding can be done at any time, when the plant is in active growth, which is normally in spring and the beginning of the rainy season. However, October to December is the best season here. In South India, July to September is the best time.
T-budding or shield-budding is easy to perform. The root-stock is generally budded at a height of about 18 cm. Often the scion of the budded plants in the field comes in contact with the soil due to deep planting or flooding of the field. Soil-borne diseases can thus enter the scion, even though the root-stock is resistant to them.
Budding at a greater height is, therefore, desirable. The rootstock is about the thickness of lead pencil. Bud wood is chosen from the rounded basal portion of semi-mature shoots of the current season’s growth. The leaf-blades are cut off, retaining the leaf-stalks around the buds. Angular bud wood is avoided. Two cuts are given in the bark of the stem of the root-stock at a proper height to form a T. The vertical cut of the T is about 1 cm long and the horizontal cut goes about halfway around the stem of the root-stock. Flaps of bark in the crotch of the T are lifted with a knife on both sides.
Shoot tip grafting has been recently standardized at N.R.C.C., Nagpur for raising Nagpur mandarin true to type and disease free.
Citrus seedlings were common in much of the world until the mid-1800. The budding or grafting of citrus was apparently practiced in the fifth century, but it was not until Phytophtora foot rot which appeared in Azores in 1842 that the transition of citriculture from seedling to budded trees began. Seedlings were gradually replaced by budding onto rootstock seedling.
The selection of rootstock for commercial citrus scion (variety) is a complicated one. A stock that may be superior for a given scion variety under particular soil and environmental conditions may turn out to be inferior for another scion variety Series of rootstock trials have been undertaken practically in every important citrus growing regions of India.
The earliest known citrus rootstock trial in India was conducted by Brown in 1920 at Peshawar (now in Pakistan). Jambhiri was suitable rootstock for orange, pummelo and lemon varieties. Later the trial conducted at Montgomery with three varieties of malta orange, Marsh Seedless grapefruit and Sangtra local revealed that for Malta Blood Red, Jatti khatti was the best and Karna Khatta the worst rootstock. Karna Khatta and rough lemon were satisfactory for Valencia orange. For grapefruit Jatti Khatti, Karna Khatta and Mithi were successful. Jaffa and Valencia showed satisfactory stionic compatibility with rough lemon.
Rootstock trial later conducted at Punjab revealed that Jatti khatti excelled all other rootstocks in imparting growth, vigour and fruit yield followed by Karna Khatta. Juice content, T.S.S. and acids were high in fruits on Poncirus trifoliata Cleopatra mandarin performed well for Blood Red and Valencia sweet orange. In compatibility between Blood Red Orange on Karna Khatta and Mosambi and Blood Red on rough lemon with clear bud union crease symptoms earlier thought to be delayed incompatibility was later confirmed a virus infestation.
In Rajasthan (Sri Ganganagar), Jatti Khatti (C. Jambhiri) is the most prevalent rootstock for kinnow mandarin and sweet orange.
Rootstock trials conducted at I.A.R.I., New Delhi revealed the superiority of Troyer Citrange, Karna Khatta and Sohsarkar (C. Kama) for Kinnow mandarin. The plants of kinnow on Troyer Citrange showed moderate plant growth, precocity high T.S.S. and acidity, bright deep orange colour of fruits and early maturity while those on Karna Khatta and Sohsarkar the plant size is increased, fruits of moderate T.S.S. reduced acidity and delayed maturity.
Thus by use of these three rootstocks fruit maturity of kinnow fruit is staggered from end of November to mid-January. Cleopatra mandarin was most ideal rootstock for sweet orange varieties – Mosumbi and Pineapple. The plants raised on this rootstock are standard sized and compact, slow to come into bearing and improved fruit quality. Karna Khatta was the next best rootstock which showed vigorous plant growth, increased fruit size of moderate quality.
Karna Khatta (C.Karna) is the rootstock used commonly in Uttar Pradesh in heavy and wet soils. Nurserymen sometimes use Citron, mokri or turanj (C. medica) as a rootstock, since it gives saleable plants at an early age, but it is otherwise a worthless rootstock.
For Khasi mandarin and other scions at Burnihat (Assam), Sohmyndong (C. jambhiri) and Sohsarkar (C. Karna) appeared suitable rootstocks.
In Maharashtra, rootstock trials were conducted at Poona, Sri Rampur, Tharsa and Nagpur. Rangpur lime was found the best followed by jambhiri for Nagpur santra and Mosumbi. The plants on Rangpur lime were most healthy, vigorous, productive, tolerant to greening and resistant to tristeza disease.
In Andhra Pradesh, Sathgudi orange on Sathgudi itself showed best bud Union, good fruit quality and withstood decline more successfully. Rangpur lime is another promising rootstock with regard to semi-dwarf nature, drought and disease resistance. The possibility of close planting of Sathgudi on Rangpur lime has been suggested.
Extensive research has been conducted on citrus rootstocks at Chethali and Gonicoppal in Karnataka. The rootstocks Rangpur lime, Cleopatra mandarin, rough lemon, Troyer citrange and trifoliate orange showed superiority taking into consideration as tree vigour, yield, lesser chlorosis and decline symptoms.
Planting Operations for Citrus:
Citrus is planted twice in a year. The spring planting season, suitable for citrus plantings, starts after the 15th of February. The monsoon season starts from middle of July and continues upto the end of September. Citrus is however, commonly planted when rains have set in and the weather has cooled down sufficiently.
Kinnow and Baramasi lemon plants can be successfully transplanted bare-rooted during December-February. After digging the plants from nursery, remove the one fourth, foliage and cover the rest with moist wrapping material.
i. Preparation of Land:
The land on which young citrus trees are to be planted should be prepared well in advance. Soil should be thoroughly ploughed up and levelled. Preferably, soil should be planted with a green-manure crop such as guara or senji. These crops should be burried when they have attained the maximum vegetative growth and field should be irrigated immediately. The land should be heavily manured with farmyard manure a few months before the actual planting.
ii. Care of Young Plants:
The young trees must be protected against high or low temperature and strong winds. The trunk of the young trees should be white washed to protect them against the hot sun. A row of Jantar (Sesbania egyptica) planted on the south-western side is very effective in reducing sunburn and wind damage to young trees. The young citrus plants are susceptible to frost and must be protected during the first two winters. This can be done by providing a cover over the young plants with farm-waste material.
The southern side of the plants should be kept open to receive sunshine. The young plants must be watered regularly in the arid regions. Apply water 2-3 times a week for the first few weeks after planting. After this, during the first year, the plants should be irrigated after a week. The sprouts which develop on the trunks of the trees below the scaffold branches should be removed. The top should be left unpruned and only the dry and dead-wood should be removed.
Flowering and Fruiting in Citrus Plant:
The flowering in citrus takes place mostly in spring and in growing season when soil moisture and temperature both remain favourable. In Lime and lemons, flowering takes place almost throughout the year. In northern Indian conditions, major bloom of almost all the species occurs during early spring (February- March) when the atmospheric temperature starts rising after the cold winter and soil moisture condition also improves.
In South India, where there is no well-defined winter with very low atmospheric temperature, the flowering season is longer and not very distinct. It is very common to get two crops, occasionally three also in many citrus types grown in South India. However, the flowering can be regulated by withholding soil moisture or through fruit thinning by chemicals and adjustment of fruit harvesting.
In Kinnow, flowering takes place during end February to early March in North India. It starts bearing flower and fruits 4-5 years after planting. It is precocious in bearing and gives very high yield during early years of its life. Due to heavy bearing the trees get exhausted leading to collapse or gradual decline.
In citrus, pollen development is a normal phenomenon except in Washington Naval, Satsuma mandarin and Bearss etc. where no viable pollen is produced. The cultivars where pollen is produced in abundance, self-pollination is a general rule. The stigma remains receptive for 6-8 days. Honey bees are common pollinating agent. Cross pollination is reported to increase seediness in certain citrus cultivars like Shamouti orange, Clementine mandarin and Minneola tangelo.
Both male and female sterility, partial self-incompatibility and normal male and female fertility conditions prevailing in genus Citrus which have resulted to different degree to seediness in the fruits, i.e. Seedless (with no seed), commercially seedless (0-10% seed) and seedy (numerous seeds). Self-incompatibility has been reported in Nepali Oblong and
Lucknow Seedless lemon, pummelo, Clementine mandarin and Sweet lime. Nagpur Santra was found to be self-compatible and cross compatible except with grapefruit.
Poor fruit set and high fruit drop resulted into poor yield, especially under unfavourable environmental conditions such as late frosts, drought or excessive rain etc. in most of the citrus species. Due to considerable loss of soil moisture during summer months leads to severe fruit drop.
The growth of the fruit as represented by a change in the diameter is rapid upto the middle of October in Hamlin and up to the end of November in Valencia Late. Therefore, the first seven and eight months after blooming are the periods of most rapid fruit growth in sweet orange varieties grown under North Indian conditions.
Increase in fruit weight and volume followed corresponding increases in fruit diameter. Rind thickness in both the varieties decreased during the early stages of maturity and thereafter remained practically unchanged. Juice percentage increased with the development of the fruit and the maximum was attained when the rate of growth had slowed down.
Training and Pruning of Citrus:
To the young citrus plants, staking should be given to help them grow, upright and straight. Sweet orange trees does not require pruning except removal of unwanted, intercrossing and diseases branches. In sour lime, the branches which are profusely growing on the ground and the water sprouts should be removed. Pruning operation provides good framework to the trees which should be attended to yearly.
Luxuriant growths of branches are in sweet lime causes overlapping and more height. It is, therefore, essential to prune the tree for maintaining even growth. In Haryana, moderate pruning of 20 kg per tree in late November to early December results in higher fruit yield of sweet lime.
In lemon, the plants should be trained in such a way to develop open centre. This can be achieved only by removal of twigs yearly. It is essential to prune lemons very light annually to stimulate new growth and maintain production.
Grapefruit trees require less pruning than orange trees. Under humid conditions, the drooping branches should be pruned to avoid infection by gummosis and foot rot fungi. Due to more dense foliage and heavier cropping, it gives out more dead wood than orange trees. Therefore, all such dead wood should be suitably pruned.
Off shoots or water sprouts are common phenomenon in Kinnow. These are characterised by long thorny growth with sparse foliage. They bear profusely but the quality of fruit is rather poor. Trees under stress are more prone to produce sprouts. The water sprouts unnecessarily rob the food material from the plant. Judicious modification of these off shoots should be done from time to time by pruning and balancing them with rest of the tree.
The pruning is carried out early in the spring after the danger of frost has passed and before the tree starts a new growth cycle. For getting better yield of high quality fruit, pruning of crowded branches is necessary to open up the tree for proper ventilation and provide more chances for inner-wood to bear fruit. Removal of dead and dried wood is necessary to check the further spread of disease.
Harvesting and Marketing of Citrus:
The fruit ripens in about nine months after flowering. The harvesting season varies in different parts of the country. In North India, the fruits ripen in winter, but there is more demand for these juicy fruits in the warmer months. Consequently, huge quantities of sour lime come every summer from Andhra Pradesh to North India. In the South, the crop matures at different times and takes fewer months to mature.
Limes and lemons flower several times a year and their fruits mature in about six months. In some places, kagzi lime fruits are available almost throughout the year. However, the main harvesting season is March-April in the Circars, April-June in the Guntur and Nellor area, June-August in North Arcot, and July-September in Rayalaseema and Western India.
Sweet limes ripen early and there is a tendency to harvest them even earlier. The Valencia orange ripens late, but its harvesting is done early to vacate the orchard. In both cases, the result is poor fruit quality. This is mostly due to the fact that the standing crop is sold to the contractors, who are anxious to take advantage of the early market and to quit the orchard as soon as possible. The packing of the fruit is poorly done, mostly in long bamboo baskets in the case of mandarins, which are more delicate, and in large gunny bags in the case of sweet oranges.
In the past, the fruit has also been directly loaded into railway wagons. Sikkim is the only place where the mandarin fruits are packed in wooden boxes. Grading of the fruit is not done, except to some extent in Coorg. In Andhra Pradesh, grading of sweet oranges was started during the Second World War but it died out. The Indian Standards Institute is now preparing standards for the marketing of oranges, etc.
The fruit is generally harvested when it begins to change its colour. However, colour is not a good criterion for harvesting. In high rainfall areas and in areas with a warm winter, the skin colour in citrus does not develop properly. The Sathgudi orange in the South rarely develops the yellow colour when it is harvested.
The Mosambi in the Pune area develops only a pale yellow colour, but it is harvested even earlier in green condition to catch the early market. Another reason for early harvesting in South India is to escape the attack of the fruit-sucking moth. This results in poor quality of fruit. The oranges and mandarins should have at least 8 per cent sugars at the time of harvesting. The acidity in most Indian varieties varies from 0.3 per cent to 0.8 per cent.
Budded sweet orange trees give a commercial crop in about five years. Mandarins may take one or two years more. Seedling trees take about eight years to come to bearing. The life of budded trees is about 35 years and of seedlings about 60 years. A good sweet orange tree bears about 500 fruits and mandarin about 1,000 to 1,500 fruits.
Sweet oranges may be kept at room temperature in North India for about a month after harvesting. However, mandarins begin to shrink and deteriorate after a week. Their storage in warmer seasons is more important. Dipping the fruits in wax emulsions increases their life, but cold storage is more effective and is now common in India. Ripe mandarins can be stored at 40°F for about three months and sweet oranges for four months at 36°-39°F. Mosambi prefers the higher temperature of 52°F.
Varieties of Citrus:
In India the loose-skin oranges or mandarins are often called oranges and the sweet orange is called malta. This causes confusion since the English word orange refers to the sweet orange. Among mandarins, there are three important types—Coorg, Khasi and Nagpuri. In Nagpur mandarin, clonea having only a few seeds (< 5 seeds/fruit), late maturity, better fruit colour and tight skin fruits of high yield have been found at National Research Centre for Citrus, Nagpur. Nagpur mandarin is propagated as a budded plant and the other two (Coorg and Khasi) as seedlings. They are all of the Ponkan type of China and their fruits and plants show little difference. The seedlings are more vigorous, spiny and erect.
All three have an excellent fruit quality. The recent introductions include Kinnow, which is reported to be resistant to sun-burn, have a richer juice, is free from granulation and suffers less from greening virus. It is commercially cultivated in North India. It has performed extremely well in Punjab, Sriganganagar, lower hills and valley area of Himachal Pradesh. Other introduced varieties are Emperor and Fuetrells early from Australia and Butwal from Nepal. The Laddu with small fruits, a vigorous tree and a good yield is grown to some extent in U.P and the Deccan. It is cultivated in the Philippines, but is not so popular in India since the fruit is not as sweet as that of the other varieties. Srinagar and Hill mandarins are two varieties recommended for U.P.
The varieties of a species of citrus, unlike those of mango, are not easy to identify. Among the sweet oranges the most important variety is the Mosambi from Maharashtra. It has a distinctive furrowed fruit, with a smooth circular areole and juice with very low (0.3%) acidity.
It is similar in taste to the Succari orange of Egypt. Another variety, the origin of which is not known, is the Sathgudi or Chini of Andhra Pradesh. It has a good flavour, but does not develop a proper skin colour or flavour under the humid conditions of South India.
A cultivar grown in the coastal areas of Andhra Pradesh is the Batavian. It is similar to the Sathgudi, but is said to be less sweet. This may be due to the fact that it is harvested very early to avoid damage from the fruit-sucking moth. Another feature of this variety is that each fruit is wrapped in a basket-like covering woven from palm leaves to protect it from the moth. The colour on the skin does not develop where the light is cut off and the fruit develops a chequered appearance.
Among the recently-introduced varieties, Pineapple is most successful in the Punjab. Its fruit has a smooth deep bright orange skin, the pulp is highly flavoured and sweet and the yield good, but it has bold seeds. Another successful variety is Malta common, which is considered to be a mixture of varieties by some people; Joppa and Vanille are also good. Hamlin is popular due to its earliness, but it shows a high percentage of dry granulated fruits on the rough lemon root-stock. Valencia bears well but ripens too late in the season.
It is usually harvested in the month of February along with other varieties, when it is still sour. It has, therefore, fallen into disrepute, because of its poor quality. Another important variety is Blood Red grown in the dry tracts of the Punjab and Rajasthan. Yuvraj Blood Red is a clonal selection of Blood Red sweet orange from Sriganganagar which is seedless and early maturing. Washington Navel develops a large fruit, which lacks both juice and quality.
Among sour limes (C. aurantifolia), there are no well-established varieties except the oval-fruited ones from Assam called Abhayapuri lime. The fruits of ordinary varieties are roundish. Recently, some superior clones of acid lime like Vikram (high yielding, fruits borne in clusters) and Pramilini (high yield, tolerant to canker) from Parbhani, Sai Sarbati (high yield, tolerant to canker and tristeza, tendency to summer cropping) from Rahuri, Chakradhar (thornless, seedless) from Maharashtra and Jai Devi from Andhra Pradesh have been identified.
Among lemons (C.limon) there are several varieties. The commonest in South India are Malta and Nepali oblong. Rajamundry and Kagzi Kalan or Baramasi are natural hybrids between limes and lemons. Self-incompatibility exists in Kagzi Kalan lemon and pummelo, any one of these should not be planted in isolation.
Pummelo and sweet orange are good pollinizers to improve yield and fruit quality of Kagzi Kalan lemon. Among grapefruits Marsh Seedless, also called Saharanpur-special in some places, Foster, Thompson and Duncan are popular. Among pummelos there are no established varieties, but considerable variation exists on account of mono-embryony. Large or small, oval, round or oblate and white or red-fleshed types are found.