🍋Citrus

• Classification of citrus was given by Tanka & Swingle (1945). Their classification system remains the most widely accepted framework for organizing the diverse citrus species and hybrids.
• Spain is largest exporter of citrus. Despite not being the largest producer, Spain dominates the global export market due to its superior post-harvest infrastructure and proximity to European markets.
• Ultra dwarf rootstock of citrus: Flying dragon. Flying dragon (Poncirus trifoliata var. monstrosa) produces extremely compact trees ideal for container gardening and ultra-high density orchards.
• Fruit ripening: 9 month after planting.

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Mandarin

- **Botanical Name:** `Citrus reticulata` - **Family:** Rutaceae - **Origin:** China - Most common among citrus fruits grown in India. Mandarin is the backbone of **India's citrus industry**, cultivated across diverse agro-climatic zones from the Nagpur region to the North-Eastern hills. - Mandarin occupies 50 % area under citrus spp.

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• Seeds of citrus don’t have dormancy so they should be sown immediately after extraction. Unlike many other fruit crop seeds, citrus seeds are recalcitrant — they lose viability rapidly upon drying, making fresh sowing essential.
• Blooming-three time in a year. The three flowering seasons (ambe bahar, mrig bahar, and hasta bahar) give mandarin growers flexibility in choosing which season to target for the commercial crop.
• Mandarins are highly susceptible to water logging. Excess soil moisture promotes root rot caused by Phytophthora fungi, which is one of the leading causes of citrus decline in India.

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• Rootstock for HDP: Troyer citrange (1.8 x 1.8 m²). Troyer citrange is a hybrid rootstock that imparts dwarfing effect and cold tolerance, making it suitable for high density planting systems.
• Rangpur lime — most promising rootstock for mandarin and sweet orange. Rangpur lime (Citrus limonia) is valued as a rootstock for its vigour, drought tolerance, and adaptability to diverse soil conditions.
• Rootstock — Adajamir [C. assamensis] are resistant to Greening.
• Spacing of lime, lemon and sweet orange is 6 m x 6 m
• Best time for Pruning — Late winter or Early spring. Pruning during this period minimizes sap bleeding and allows new growth to harden before the next fruiting season.

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• Mandarin, sweet orange, Acid lime, grape fruit: Highly polyembryonic. Polyembryony means a single seed contains multiple embryos — most of these are nucellar (genetically identical to the mother plant), making them valuable for raising uniform rootstock seedlings.
• Pummelo, Tahiti lime, Citron: Monoembryonic. These species produce only one embryo per seed, which is typically of zygotic (sexual) origin.
• Citrus fruits have a special kind of fruit skin referred as ‘leathery rind’. The rind (also called the pericarp) consists of an outer coloured layer (flavedo) rich in essential oils and an inner white layer (albedo) rich in pectin.

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• Citrus is micro-nutrient loving plant. Citrus has high requirements for zinc, manganese, iron, and boron, and deficiencies of these elements are common and frequently limit productivity.
• Trifoliate orange-resistant to phytopthora and nematodes.
• Limolin-glycoside is responsible for bitter taste of citrus fruit juice.
• Nagpur mandarin was introduced in India in 1894 by Shuji Raja Bhosle.
• Irrigation requirement of mandarin is higher than other citrus species.
• Weeds are serious problem in nursery. So, bromocial is most effective weedicide in controlling monocot and dicot weed.
• State with highest production of citrus in India is Andhra Pradesh followed by Maharastra.
• Sikkim is the only place where mandarin are packed in wooden boxes.

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Varieties

• Coorg: Most important commercial variety in South India (Karnataka). Coorg mandarin is known for its excellent flavour and deep orange colour.
• Kodai orange: Tamil Nadu
• Khasi: Locally known as Sikkim or Kamla mandarin. (North-East India). The Khasi mandarin is one of the best-quality mandarins in India, grown in the hilly terrains of Meghalaya and Assam.
• Nagpur Santra (Ponkan): Finest mandarin in the world. Grown in Satpuda hills in Maharashtra. Nagpur Santra enjoys a GI tag and is renowned for its juiciness, deep orange colour, and sweet-acidic balance.
• Laddu mandrain
• Sutwal: Introduced from Nepal.
• Satsuma (seedless): Commercial mandarin of Japan. Satsuma’s seedless nature and easy-to-peel skin make it extremely popular in international markets.
• Emperor and Fuetrelles: Introduction from Australia.

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Kinnow

• It is high yield mandarin and cross between King Sweet x Willow Leaf mandarins
• Developed by H.B. Frost, USA -1935.
• Kinnow was introduced in India in 1959.
• It was first introduced in Punjab. Since then, Punjab has become the leading producer of Kinnow in India, with the crop playing a vital role in the state’s horticultural economy.
• It’s juicier than oranges and is majorly grown in Punjab, Himachal Pradesh, Jammu & Kashmir, Rajasthan and even Haryana.
• Kinnow can be grown in high density planting by using ‘Troyer citrange’ as a rootstock by spacing the plants at 1.8 x 1.8 m² (3000 plants/hac).
• A kinnow is generally dark in colour while the colour of an orange varies from saffron to light orange colour.

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Sweet Orange

• Botanical Name: Citrus sinensis
• Family: Rutaceae
• Origin: China
• Pre-harvest fruit drop is common in citrus. It is due to:
  • Physiological factors
  • Pathological factors
• Control measure-spray of 2, 4-D (20 PPM). Most prone variety Mosambi & Blood Red. 2,4-D is a synthetic auxin that prevents the formation of the abscission layer at the fruit stalk, thereby reducing premature fruit drop.
• Degreening of citrus fruits is done by CaC₂ (Calcium Carbide). Degreening is the process of removing the green colour from the rind of mature fruits. In tropical climates, citrus fruits may remain green even when internally mature, so degreening improves their market appeal.

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• Best time for pruning — late winter or early spring.
• Sweet orange is susceptible to water logging and phytopthora rot, so water stagnation in orchard should be avoided. Proper drainage is essential in sweet orange orchards to prevent root rot and gummosis caused by Phytophthora species.
• Double ring method - best for irrigation. In this method, two concentric rings are made around the tree, and water is applied between them. This ensures water reaches the active root zone without wetting the trunk, preventing collar rot.
• Deficiency of zinc along with N, is major nutritional problem of sweet orange. Zinc deficiency causes mottle leaf (interveinal chlorosis), which is one of the most common and visible nutrient disorders in citrus.
• Rangpur lime is the best rootstock for mosambi.
• ‘T’ budding or Patch budding are most common method for sweet orange propagation. These budding techniques ensure true-to-type plants with faster and more uniform fruit production compared to seedling trees.

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• Pineapple and Valencia - indicator of greening.

Varieties

• Hamlin: Early variety
• Jaffa: Mid-season variety
• Pineapple: Mid-season variety
• Valencia: late season variety
• Mosambi: Most popular in Maharashtra, Best rootstock— Rangpur lime. Mosambi is prized for its mild, non-acidic juice, making it the dominant variety in India’s juice industry.
• Satgudi: Most popular in Andhra Pradesh, Best rootstock— Rough lemon.
• Blood red: Most popular in North India Best rootstock— Karnakhatta, Jatti khatha. The blood red variety gets its name from the distinctive red-pigmented flesh caused by anthocyanin pigments that develop during cool night temperatures.
• Shamouti: Seedless variety
• Washinghton navel
• Batavin
• Mudkhed - Bud mutant of Nagpur mandarin.

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Lime/ Kagzi Lime (Khata Nimbu or Chota nimbu)

• India rank 5^th among major lime and lemon producing country in the world.
• Sweet lime: Citrus limetoides, Native-India, self-incompatible.
• Tahiti lime: Citrus latifolia — seedless triploid. Being a triploid, Tahiti lime is naturally seedless, making it highly desirable for the beverage and culinary industries.
• Rangpur lime: Citrus limenica, native - India
• Pummelo: Citrus grandis (largest fruit), self-incompatible. Pummelo produces the largest fruits in the citrus family, sometimes weighing over 2 kg.
• Acid lime is only propagated by seeds. Since acid lime is highly polyembryonic, seed-raised plants are mostly nucellar and therefore genetically uniform, making seed propagation both practical and reliable.

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• Kagzi lime (C. aurantifolia) is the indicator plant for Tristeza (highly susceptible to this disease). Kagzi lime is used as a diagnostic indicator because it shows clear, early symptoms of Tristeza virus infection, helping researchers detect the disease in an area.
• Citrus canker is most serious disease of acid lime. Canker causes raised, corky lesions on leaves, fruits, and stems, severely reducing fruit quality and marketability.
• Acid-lime is tropical plant.
• Lemons are divided into 4 groups:
  • Eureka
  • Lisbon
  • Anamalous

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Sweet lemon

• Gajanimma (Citrus Pennivesiculata) is most promising rootstock followed by rough lemon for acid lime.
• Sweet lime contain — nonacid juice. The juice of sweet lime has a neutral pH, making it mild and pleasant, which is why it is a popular choice for patients recovering from illness.
• Sweet lime is resistant to greening.

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Acid lime/kagzi lime varieties

• Pramalini: Canker tolerant
• Vikram
• Chakradhar: Seedless variety of Acid lime. Seedless acid lime varieties are increasingly in demand for the processing industry and export market.
• PKM-1
• Sai sarbati: Tolerant to tristiza and canker. This dual disease tolerance makes Sai Sarbati a highly valuable variety for regions where both diseases are prevalent.
• Jai devi: Pleasant Aroma
• Sweet lime Varieties
  • Mitha chikna
  • Mithotra
• Lemon Varieties
  • Eureka
  • Lucknow seedless
  • Lisbon
  • Kagzikalan
  • Nepali oblong
  • Nepali round
  • Pant lemon-I-self-incompatible.
  • Villafrance - belong to Eureka group.

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Grape Fruit

- **Botanical Name:** Citrus paradisi - **Family:** Rutaceae - Grape fruit is also known as **forbidden fruit**/ **breakfast fruit**. It is called **breakfast fruit** due to the Western tradition of consuming grapefruit at breakfast, valued for its tangy, refreshing taste and high **vitamin C** content. - Citron -- Persian apple. - Citron -- glucoside present-Hespiridin. - **Varieties** - **Star ruby:** From Hudson grape fruit through mutation breeding. **Mutation breeding** using **gamma irradiation** produced Star Ruby, which has the **deepest red flesh** among all grapefruit varieties. - Red Blush - **Duncan** - Marsh Seedless - Foster - Triumph - Sharanpur Special - Thompson

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Flowering in Citrus

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Diseases of Citrus

• Gummosis: Phytophthora spp. This disease causes the bark at the base of the trunk to crack and exude gum, eventually girdling the tree and causing death. It is especially severe in poorly drained soils.

- **Bacterial canker:** Xanthontonas compestris p.v. citri (transmitted by leaf minor). The **leaf miner** creates **wounds** on leaves that serve as **entry points** for the canker bacterium, making concurrent management of both pest and disease essential.

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• Citrus greening:
  • Earlier Mycoplasma (now causal organism is Caliberobacter, a gram negative, walled, bacteria). Citrus greening (also called HLB — Huanglongbing) is considered the most devastating citrus disease worldwide, causing lopsided, bitter, green fruits and eventual tree death.
  • Transmitted by citrus psylla, Diaphorina citri

- **Tristeza:** Virus (vector is aphids: Toxoptera sp.). **Citrus Tristeza Virus (CTV)** causes **quick decline** of trees budded on susceptible rootstocks like sour orange, and has destroyed millions of citrus trees globally.

- **Exocortis:** Viroids. **Exocortis** is caused by the smallest known plant pathogen -- a **viroid** (naked RNA without a protein coat). It produces **bark scaling** on susceptible rootstocks.

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Physiological disorder

• Granulation: Due to high temperature & R.H. during ripening. It is managed by spray lime & application of 2, 4-D (12 ppm). The juice vesicle become hard, enlarged and turn opaque grayish in colour. Granulation is also called crystallization — the juice vesicles lose their juice and become dry and granular, severely reducing fruit quality and consumer acceptance.

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• Fruit Cracking
  • It is due to sudden changes in temperature and also due to moisture stress condition. Irregular irrigation (alternating drought and heavy watering) causes the rind to lose elasticity and crack as the pulp expands rapidly after water uptake.
• Yellow leaf of citrus: Mo deficiency. Molybdenum (Mo) is a micronutrient essential for nitrogen metabolism, and its deficiency leads to characteristic yellowing of citrus leaves.
• Die back due to: Copper deficiency
• Exanthema: Copper deficiency.
• Little leaf: Copper deficiency
• Mottle leaf: Zinc deficiency. Zinc deficiency is the most common and widespread micronutrient disorder in citrus, causing an irregular pattern of green and yellow patches (mottling) on leaves.
• Citrus Decline

Citrus decline is a complex disorder resulting from the combined effect of multiple factors including nutrient deficiencies, diseases (greening, Tristeza), nematodes, and poor management practices, leading to progressive deterioration of tree health and yield.

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Insect-pest

• Psylla: Diaphorina ctri (vector of greening disease). Citrus psylla is not only a direct pest (causing leaf curling by sucking sap) but more importantly acts as the vector that transmits the devastating greening disease from infected to healthy trees.

- **Leaf minor:** Phyllocnistis curella (vector of citrus canker). The **serpentine mines** created by the larva on young leaves serve as **entry points** for the canker bacterium, making leaf miner management critical for canker control.

- **Aphids:** Toxoptera auranti (vector of Tristeza disease). - **Lemon butterfly:** Pupil demoleus. (Controlled by bagging of fruits). The large caterpillars of this **swallowtail butterfly** can **completely defoliate** young citrus trees.

- **Fruit sucking moth:** Othreis fullonica (only adult suck the juice from ripening fruits). Unlike most insect pests where **larvae cause damage**, in fruit sucking moth it is the **adult moth** that pierces the rind with its proboscis and sucks out the juice, causing fruits to rot.

## Summary Cheat Sheet

Concept / Topic	Key Details
Citrus genus	Citrus spp.; Family Rutaceae
Origin	Northeast India and Southeast Asia
Mandarin orange	C. reticulata; Nagpur mandarin most famous
Sweet orange (Mosambi)	C. sinensis; Jaffa, Valencia, Sathgudi
Acid lime (Kagzi nimbu)	C. aurantiifolia; Pramalini, Vikram
Lemon	C. limon; Eureka, Lisbon
Grapefruit	C. paradisi
Kinnow	Mandarin hybrid (King x Willow Leaf); Punjab
Propagation	T-budding, air layering; rootstock = Rangpur lime
Major disease	Citrus canker (Xanthomonas citri)
Major disease	Greening / HLB (Candidatus Liberibacter)
Major disease	Tristeza (CTV virus); spread by Toxoptera citricida
Gummosis	Phytophthora spp.; trunk oozing gum
Major pest	Citrus psylla, leaf miner, fruit fly
Fruit type	Hesperidium (modified berry)
Polyembryony	Multiple embryos per seed; common in citrus