🍊 Subtropical Fruits — Citrus, Grapes, Apple & Litchi
Learn citrus, grape, apple and litchi cultivation for CUET Agriculture. Rootstock selection, budding, training systems and cold storage.
Subtropical fruits occupy a unique niche -- they require moderate climates that are neither fully tropical nor fully temperate. This group includes some of India's most economically valuable fruit crops: Citrus, Grapes, Apple, and Litchi. A key exam concept: most subtropical fruits are non-climacteric (they do not ripen after harvest), except Apple which is climacteric.
3. Citrus (Citrus spp.)
Citrus (Citrus spp.) — Source: Wikimedia Commons (CC)
- Family: Rutaceae
- Origin: North-East India and South-East Asia (often described as the "Citrus triangle" -- NE India, Myanmar, and Malaysia)
- India ranks third in citrus production after China and Brazil
NOTE
Citrus is believed to have originated in the North-East India to South-East Asia region. This "Citrus triangle" is considered the primary centre of diversity for citrus species.
Major Citrus Crops
| Crop | Species | Key Varieties |
|---|---|---|
| Sweet orange | C. sinensis | Mosambi, Jaffa, Blood Red, Sathgudi, Pineapple |
| Mandarin orange | C. reticulata | Nagpur mandarin (Nagpur santra), Khasi mandarin, Coorg mandarin, Kinnow (King x Willowleaf) |
| Lemon | C. limon | Eureka, Lisbon, Assam lemon |
| Acid lime | C. aurantiifolia | Kagzi lime, Pramalini, Vikram, Sai Sarbati |
| Grapefruit | C. paradisi | Marsh Seedless, Duncan |
| Pummelo | C. grandis | -- |
Kinnow -- India's Most Exported Citrus
Kinnow is a hybrid between King mandarin and Willowleaf mandarin, developed at the University of California. It is extensively grown in Punjab and Rajasthan and is India's most exported citrus fruit. Kinnow has excellent juice content (50%) and flavour but has a short shelf life due to its loose rind. The Punjab Agricultural University has released improved seedless Kinnow selections to enhance export competitiveness.
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Subtropical fruits occupy a unique niche -- they require moderate climates that are neither fully tropical nor fully temperate. This group includes some of India's most economically valuable fruit crops: Citrus, Grapes, Apple, and Litchi. A key exam concept: most subtropical fruits are non-climacteric (they do not ripen after harvest), except Apple which is climacteric.
3. Citrus (Citrus spp.)
Citrus (Citrus spp.) — Source: Wikimedia Commons (CC)
- Family: Rutaceae
- Origin: North-East India and South-East Asia (often described as the "Citrus triangle" -- NE India, Myanmar, and Malaysia)
- India ranks third in citrus production after China and Brazil
NOTE
Citrus is believed to have originated in the North-East India to South-East Asia region. This "Citrus triangle" is considered the primary centre of diversity for citrus species.
Major Citrus Crops
| Crop | Species | Key Varieties |
|---|---|---|
| Sweet orange | C. sinensis | Mosambi, Jaffa, Blood Red, Sathgudi, Pineapple |
| Mandarin orange | C. reticulata | Nagpur mandarin (Nagpur santra), Khasi mandarin, Coorg mandarin, Kinnow (King x Willowleaf) |
| Lemon | C. limon | Eureka, Lisbon, Assam lemon |
| Acid lime | C. aurantiifolia | Kagzi lime, Pramalini, Vikram, Sai Sarbati |
| Grapefruit | C. paradisi | Marsh Seedless, Duncan |
| Pummelo | C. grandis | -- |
Kinnow -- India's Most Exported Citrus
Kinnow is a hybrid between King mandarin and Willowleaf mandarin, developed at the University of California. It is extensively grown in Punjab and Rajasthan and is India's most exported citrus fruit. Kinnow has excellent juice content (50%) and flavour but has a short shelf life due to its loose rind. The Punjab Agricultural University has released improved seedless Kinnow selections to enhance export competitiveness.
Climate & Soil
- Subtropical to tropical; 15-30 degrees C ideal
- Sensitive to frost (especially lemon which is the most frost-sensitive citrus)
- Well-drained sandy loam; pH 5.5-7.0
- Saline and alkaline soils are detrimental -- citrus is more sensitive to poor soil conditions than many other fruit crops
Propagation
- T-budding (shield budding) -- the most common commercial method for citrus propagation. A T-shaped cut is made on the rootstock bark, and a bud shield from the desired variety is inserted.
- Rootstocks: Rough lemon (most vigorous), Rangpur lime, Jambhiri, Trifoliate orange (Poncirus trifoliata)
- Trifoliate orange is a particularly important rootstock -- it is resistant to Phytophthora (foot rot), induces dwarfing (allowing closer planting), and provides cold tolerance
Planting
- Spacing: 6m x 6m (mandarin), 5m x 5m (acid lime)
- Pit size: 75cm x 75cm x 75cm
- Planting: July-August (monsoon) or February-March
Manuring (bearing tree, per tree)
- Mandarin: 600g N + 200g P2O5 + 100g K2O + 20 kg FYM
- Apply in two splits: before flowering and after fruit set
- Foliar spray of ZnSO4 (0.5%) + MnSO4 (0.3%) for micronutrient deficiency -- zinc and manganese deficiencies are very common in citrus and cause reduced fruit quality
Irrigation
- Basin irrigation or drip irrigation
- Withholding irrigation for 1-2 months before flowering is a deliberate practice called bahar treatment. The water stress forces the tree to shed leaves and enter a rest period; when irrigation is resumed, the tree flowers profusely.
- Three types of flowering (bahar) in citrus:
- Ambia bahar (January-February) -- main crop in Central India; fruits mature in winter (best quality)
- Mrig bahar (June-July) -- flowering after monsoon rains
- Hasth bahar (September-October) -- least preferred due to hot weather during fruit development
IMPORTANT
Bahar treatment (withholding irrigation to regulate flowering time) is practiced in both Citrus and Pomegranate. In citrus, Ambia bahar is the preferred flowering season in Central India, while in pomegranate, Mrig bahar is most preferred. Do not confuse the two.
Harvesting & Yield
- Non-climacteric fruit -- must be harvested only when fully mature because citrus does not ripen further after picking
- Maturity index: TSS:Acid ratio -- Mandarin: 10:1, Sweet orange: 12:1. The ratio increases as the fruit matures (sugar increases, acid decreases).
- Yield: Mandarin 15-20 t/ha; Acid lime 10-15 t/ha
Important Diseases & Pests
- Citrus canker (Xanthomonas citri) -- produces characteristic raised, corky, crater-like lesions on leaves, stems, and fruits. Controlled by spraying copper oxychloride.
- Greening/HLB (Huanglongbing) (Candidatus Liberibacter) -- the most devastating citrus disease worldwide; causes blotchy mottle on leaves and lopsided, bitter fruits. Transmitted by citrus psylla (Diaphorina citri). There is no cure; management relies on vector control and planting disease-free nursery stock.
- Citrus tristeza virus (CTV) -- transmitted by Toxoptera citricida (brown citrus aphid); causes quick decline of trees on susceptible rootstocks. Resistant rootstocks like Trifoliate orange provide protection.
- Phytophthora gummosis -- foot rot/gummosis caused by Phytophthora spp.; gummy exudate oozes from the bark near the soil line. Use resistant rootstock (Trifoliate orange).
- Citrus leaf miner (Phyllocnistis citrella) -- larvae create serpentine mines (winding silvery trails) on young leaves
6. Grapes (Vitis vinifera)
Grapes (Vitis vinifera) — Source: Wikimedia Commons (CC)
- Family: Vitaceae
- Origin: Armenia and Eastern Turkey (Near Caspian Sea)
- Chromosome number: 2n = 38
Climate & Soil
- Temperate to subtropical; dry hot climate is ideal for producing quality grapes (sugar accumulation requires warm, dry conditions)
- Rainfall during ripening causes berry cracking and botrytis rot -- this is why Maharashtra's hot, dry climate produces India's best grapes
- Well-drained sandy loam; pH 6.5-7.5
- Major grape-producing states: Maharashtra (Nashik, Sangli, Solapur), Karnataka, Tamil Nadu, AP
Important Varieties
| Category | Varieties |
|---|---|
| Table (seeded) | Anab-e-Shahi, Bangalore Blue (Isabella), Gulabi |
| Table (seedless) | Thompson Seedless, Sonaka, Tas-A-Ganesh, Sharad Seedless, Manik Chaman |
| Wine | Cabernet Sauvignon, Shiraz, Chenin Blanc |
| Raisin | Thompson Seedless, Kishmish |
TIP
Thompson Seedless is India's most important grape variety -- it serves triple purpose: table, raisin, and wine production. Most of India's grape exports are Thompson Seedless.
Propagation
- Hardwood cuttings -- the most common method; 2-3 budded cuttings taken from mature, dormant canes during pruning season
- Rootstocks: Dogridge (110R), Salt Creek (most salt-tolerant), 1613C -- rootstocks are used in areas with nematode, phylloxera, or salinity problems
Training Systems
Training systems provide structural support for grape vines and optimize sunlight exposure:
- Head system / Bush system -- traditional in Maharashtra; vine grows as a free-standing bush
- Bower / Pandal system -- flat overhead canopy; the most common training system in India; produces high yield but can reduce berry quality due to shading
- Telephone / Kniffin system -- bilateral cordon on wires
- Y-trellis -- improved light interception compared to bower system; recommended for quality grape production as it allows better air circulation and light distribution
Pruning
Grapes in tropical India follow a unique two-season pruning system because there is no natural winter dormancy:
- April pruning (back pruning) -- heavy pruning that removes most of the previous season's growth; stimulates vegetative growth (shoots and leaves) during the monsoon
- October pruning (forward/fruit pruning) -- light pruning of the newly grown canes; triggers fruiting during the dry winter-spring season
- Use Gibberellic acid (GA3) at 25-50 ppm for berry elongation (in seedless varieties) and cluster thinning to produce larger, well-shaped bunches
Harvesting & Yield
- Non-climacteric fruit -- must be harvested at the right maturity since no further ripening occurs
- Maturity: TSS 20-24 degrees Brix for table grapes; TSS:Acid ratio 25-35:1
- Yield: 20-30 tonnes/ha
- Pre-cooling and SO2 fumigation for export -- SO2 controls Botrytis bunch rot during cold storage and transport
7. Apple (Malus domestica)
Apple (Malus domestica) — Source: Wikimedia Commons (CC)
- Family: Rosaceae
- Origin: Central Asia (Kazakhstan -- M. sieversii) -- the wild ancestor of cultivated apple still grows in the mountains of Kazakhstan
- Chromosome number: 2n = 34
- Requires chilling hours (800-1600 hrs below 7 degrees C) -- this cold requirement is essential for breaking winter dormancy and ensuring uniform budbreak and flowering in spring
IMPORTANT
Apple requires 800-1600 chilling hours (hours below 7 degrees C during winter). This is why apple cultivation in India is restricted to the Himalayan states at elevations above 1500m. Low-chilling varieties like Anna and Dorsett Golden are being tried in subtropical areas.
Climate & Soil
- Temperate climate; altitude 1500-2700 m MSL
- Major states: Jammu & Kashmir (largest producer), Himachal Pradesh, Uttarakhand, Arunachal Pradesh
- Deep, well-drained loamy soil; pH 5.5-6.5
Important Varieties
- Delicious group: Royal Delicious, Red Delicious, Starking Delicious, Red Chief
- Cooking: Golden Delicious, Granny Smith
- Low chilling: Anna, Dorsett Golden, Tamma (for subtropical areas where chilling hours are insufficient for regular varieties)
- Rootstocks: M9 (most dwarfing), M26, MM106, MM111, Crab apple seedlings. M9 is the most widely used rootstock for high-density apple orchards worldwide.
Propagation
- Tongue grafting -- the most common method (performed in January-February during dormancy)
- T-budding -- also practiced (June)
- Clonal rootstocks are propagated by stooling/mound layering -- the mother plant is mounded with soil, which induces rooting on the buried stems
Planting
- Spacing: 10m x 10m (seedling rootstock); 3m x 1m to 3.5m x 1.5m (high density on M9)
- Pollinizers are essential -- apple is self-incompatible, meaning pollen from the same variety cannot fertilize its own flowers. Every orchard must include pollinizer varieties (different varieties that bloom at the same time) to ensure cross-pollination and fruit set.
Self-Incompatibility in Apple — Why Pollinizers Are Mandatory
Apple exhibits gametophytic self-incompatibility controlled by the S-gene locus. When pollen lands on a stigma with the same S-alleles, the pollen tube growth is inhibited and fertilization cannot occur. This means an orchard planted with only one variety will produce almost no fruit, regardless of bee activity. The standard recommendation is to plant 1 pollinizer tree for every 8-9 main variety trees, arranged so that no tree is more than 2 rows away from a pollinizer.
Manuring (bearing tree)
- 350g N + 175g P2O5 + 350g K2O + 35 kg FYM per tree
- Calcium spray is important for preventing bitter pit -- a calcium-deficiency disorder that causes small, sunken, bitter-tasting spots on the fruit
Harvesting & Yield
- Climacteric fruit -- continues ripening after harvest (unlike most other fruits in this lesson)
- Harvest maturity indicators:
- Starch-iodine test (iodine stains starch dark blue; as apple ripens, starch converts to sugar, and staining decreases)
- Change in ground colour (background colour changes from green to yellow)
- Firmness (measured by penetrometer)
- TSS and days after full bloom
- Yield: 10-20 t/ha (conventional); up to 80 t/ha (high density on M9 rootstock) -- a dramatic 4-8x increase, which is why HDP is transforming apple production
- CA storage (Controlled Atmosphere) -- 2-3% O2, 1-3% CO2, 0-1 degrees C extends shelf life to 6-8 months. By reducing oxygen and increasing CO2, respiration and ripening are dramatically slowed.
8. Litchi (Litchi chinensis)
Litchi (Litchi chinensis) — Source: Wikimedia Commons (CC)
- Family: Sapindaceae
- Origin: Southern China (Guangdong, Fujian provinces)
- Chromosome number: 2n = 30
- Bihar is the largest producer in India, contributing about 70% of national production -- the Muzaffarpur district is especially famous for litchi
Climate & Soil
- Subtropical; requires cool dry winters (for flower initiation) and hot humid summers (for fruit development)
- Frost-free areas essential; annual rainfall 1000-1500 mm
- Well-drained deep loamy soil, rich in organic matter; pH 5.0-7.0
- Sensitive to alkaline and saline soils -- litchi requires slightly acidic conditions
Important Varieties
- Early: Shahi (Rose Scented), Early Bedana (seedless -- the seed aborts during development)
- Mid-season: China, Dehradun, Calcuttia
- Late: Purbi, Late Bedana, Kasba
Propagation
- Air layering (gooti) -- the most common and successful method for litchi; performed during June-July (monsoon) when humidity is high, which promotes root formation at the girdled site
- Veneer grafting is also practiced but with lower success rate
Planting
- Spacing: 10m x 10m -- litchi trees grow very large and need ample space
- Planting: July-August (monsoon)
- Windbreaks are essential -- litchi is extremely sensitive to hot dry winds which cause "sunburn" (desiccation of leaves and young fruits). Rows of tall trees like Eucalyptus or Casuarina are planted as windbreaks around litchi orchards.
Harvesting & Yield
- Non-climacteric fruit -- must be harvested at the right stage since no further ripening occurs
- Harvest when fruit colour turns pinkish-red and the spines on the pericarp flatten (become less prominent)
- Yield: 80-100 kg/tree (mature bearing tree)
- Fruit cracking -- the major physiological problem of litchi; caused by fluctuations in soil moisture (especially when dry periods alternate with heavy rain). Maintaining uniform soil moisture through mulching and regular irrigation is the best preventive measure.
- Pericarp browning -- a major post-harvest problem; the beautiful red pericarp turns brown within 24-48 hours of harvest due to enzymatic browning (polyphenol oxidase activity). Treatments include SO2 fumigation or acid dip (dilute HCl) which inactivate the browning enzymes and maintain the red colour.
TIP
Remember litchi's two major problems: Fruit cracking (pre-harvest -- caused by uneven moisture) and Pericarp browning (post-harvest -- caused by enzymatic browning). Both are among the most commonly asked CUET questions on litchi.
Summary Cheat Sheet
| Concept / Topic | Key Details / Explanation |
|---|---|
| Citrus — family & origin | Rutaceae; Origin: North-East India (Assam); 2n = 18 |
| Citrus — fruit type | Hesperidium (modified berry with leathery rind); juice vesicles = edible part |
| Citrus — fruit parts | Flavedo (outer colored rind), Albedo (white spongy layer), segments with juice vesicles |
| Citrus — propagation | T-budding (most common); also shield budding |
| Citrus — key varieties | Nagpur Mandarin (Santra), Khasi Mandarin, Coorg Mandarin, Kinnow (King × Willow Leaf hybrid) |
| Citrus — disorders | Citrus canker (Xanthomonas citri), Citrus greening/HLB (Candidatus Liberibacter), Tristeza virus (aphid), Granulation (dry juice vesicles) |
| Citrus — production | Maharashtra leads (Nagpur — "Orange City"); non-climacteric fruit |
| Grapes — family & origin | Vitaceae; Origin: Armenia (Near East); 2n = 38 |
| Grapes — training | Bower/Pandal system (most common in India); also Kniffin, Head system |
| Grapes — propagation | Hardwood cuttings (most common); also grafting on Dogridge rootstock (salt-tolerant) |
| Grapes — key varieties | Thompson Seedless (Sultanina — most popular), Sharad Seedless (black), Anab-e-Shahi, Bangalore Blue (juice/wine) |
| Grapes — GA₃ use | Induces parthenocarpy (seedlessness) and berry enlargement; also berry thinning |
| Grapes — production | Maharashtra leads (Nashik — "Grape Capital"); non-climacteric; 2 crops/year possible |
| Apple — family & origin | Rosaceae; Origin: Central Asia (Kazakhstan); 2n = 34 |
| Apple — chilling | Requires 1000-1600 hours below 7°C; Dormex (hydrogen cyanamide) used to break dormancy in low-chill areas |
| Apple — pollination | Self-incompatible — requires pollinizer varieties (e.g., Golden Delicious, Red Gold) |
| Apple — key varieties | Red Delicious, Royal Delicious, Golden Delicious, Ambri (Kashmir local), Anna (low-chill) |
| Apple — rootstocks | Malling series — M9 (ultra-dwarf), MM106 (semi-dwarf); EMLA = virus-free clones |
| Apple — production | J&K leads; climacteric fruit; propagated by tongue grafting |
| Litchi — family & origin | Sapindaceae; Origin: South China; 2n = 28-30; "Queen of Fruits" |
| Litchi — fruit type | Nut with fleshy aril (edible part); non-climacteric |
| Litchi — propagation | Air layering (gooti) — most common; June-July (monsoon) |
| Litchi — key varieties | Shahi (Rose Scented), China, Dehradun, Calcuttia, Early Bedana (seedless) |
| Litchi — disorders | Fruit cracking (uneven soil moisture — pre-harvest); Pericarp browning (enzymatic — post-harvest; treated with SO₂ fumigation) |
| Litchi — production | Bihar leads; sensitive to hot dry winds — needs windbreaks |
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