Unit2 - Subjective Questions

Horticultural crops are classified into three major groups based on their life span or life cycle:

1. Annuals:

• Plants that complete their life cycle (from seed germination to seed production) in one growing season or year.
• Examples: Tomato, Brinjal, Okra, Marigold, Coleus.

2. Biennials:

• Plants that require two seasons to complete their life cycle.
• In the first season, they undergo vegetative growth and store food. In the second season, they produce flowers and seeds.
• Examples: Onion, Cabbage, Carrot, Radish (when grown for seed production).

3. Perennials:

• Plants that live for more than two years.
• They may be woody (trees and shrubs) or herbaceous.
• They usually bear fruits/flowers annually after reaching maturity.
• Examples: Mango, Apple, Citrus, Coconut, Banana (herbaceous perennial).

The classification is based on the respiration rate and ethylene production during ripening.

The Cucurbitaceae family is one of the largest families of vegetable crops, commonly known as the Gourd family. They are generally warm-season crops, tendrils-bearing vines, and usually monoecious (separate male and female flowers on the same plant).

Major crops in this family include:

1. Cucumber: Cucumis sativus ()
2. Bitter Gourd: Momordica charantia ()
3. Watermelon: Citrullus lanatus ()
4. Bottle Gourd: Lagenaria siceraria ()
5. Muskmelon: Cucumis melo ()
6. Pumpkin: Cucurbita moschata ()

Most produce pepo type fruits and thrive in hot climates.

Soil pH is a measure of the acidity or alkalinity of the soil. It is defined as the negative logarithm of hydrogen ion concentration:

Impact on Nutrient Availability:

• Optimum Range: Most horticultural crops thrive in a pH range of 6.0 to 7.0, where most nutrients are readily available.
• Acidic Soils (): availability of Nitrogen (N), Phosphorus (P), Potassium (K), Sulphur (S), Calcium (Ca), and Magnesium (Mg) decreases. However, micronutrients like Iron (Fe), Manganese (Mn), and Zinc (Zn) become highly soluble and may reach toxic levels.
• Alkaline Soils (): Availability of micronutrients (Fe, Mn, Zn, Cu, B) decreases significantly, leading to deficiency symptoms (e.g., Iron chlorosis). Phosphorus gets fixed with Calcium.

Crop Preference:

• Acid tolerant: Blueberry, Potato, Sweet Potato.
• Alkaline tolerant: Date palm, Ber, Aonla.

Horticultural crops are broadly classified into three groups based on the temperature zones they are adapted to:

1. Tropical Crops:

• Require hot and humid climate.
• Cannot tolerate frost or low temperatures.
• Optimum temperature: to .
• Examples: Mango, Banana, Papaya, Pineapple, Coconut, Cashew.

2. Sub-tropical Crops:

• Intermediate group; require hot summers and mild winters.
• Can tolerate minor frost.
• Examples: Citrus, Guava, Pomegranate, Grape, Litchi, Fig.

3. Temperate Crops:

• Require distinct winter season with low temperatures for dormancy breaking (Chilling requirement).
• Shed leaves during winter (Deciduous).
• Examples: Apple, Pear, Peach, Plum, Cherry, Strawberry, Walnut.

Photoperiodism is the physiological reaction of plants to the length of day (light duration) or night. It specifically governs flowering.

Classification:

1. Long Day Plants (LDP):

   • Require a day length above a critical duration (usually hours) to flower.
   • Usually temperate/winter crops that flower in late spring/summer.
   • Examples: Potato, Onion, Cabbage, Cauliflower, Carrot, Radish, Spinach.

2. Short Day Plants (SDP):

   • Require a day length shorter than a critical duration (usually hours) to flower.
   • Usually tropical/subtropical crops.
   • Examples: Sweet Potato, Cluster bean, Winged bean, Indian bean.

3. Day Neutral Plants (DNP):

   • Flowering is not affected by the length of the day.
   • They flower readily throughout the year provided temperature is favorable.
   • Examples: Tomato, Brinjal, Chilli, Okra, Cucurbits.

Solanaceae (Nightshade family) includes some of the most economically important vegetable crops. They are generally grown for their fruits (berries) or tubers.

Important Crops:

1. Potato: Solanum tuberosum () - Edible part: Tuber.
2. Tomato: Solanum lycopersicum (formerly Lycopersicon esculentum) () - Edible part: Berry.
3. Brinjal (Eggplant): Solanum melongena () - Edible part: Berry.
4. Chilli / Capsicum: Capsicum annuum () - Edible part: Berry.

Characteristics:

• Flowers are usually bisexual and actinomorphic.
• Fruit is a berry or capsule.
• Contains alkaloids (e.g., Solanine in potatoes).

Temperature is the most critical climatic factor influencing plant distribution, growth rate, and fruit quality.

1. Physiological Processes:

• Photosynthesis: Increases with temperature up to an optimum (), then declines.
• Respiration: Increases with temperature. High night temperatures consume stored carbohydrates, reducing yield.

2. Chilling Requirement:

• Temperate fruits (Apple, Pear) require a specific number of hours below (Chilling hours) during winter to break bud dormancy and flower in spring.

3. Vernalization:

• Certain vegetables (Cabbage, Carrot) require exposure to low temperatures to induce flowering.

4. Color and Quality:

• Red color development in apples requires low temperatures.
• High temperature causes sunscald in vegetables like tomato and onion.
• Lycopene formation in tomatoes is inhibited above .

5. Temperature Stress:

• Freezing injury: Ice formation inside cells destroys tissues.
• Heat injury: Desiccation and protein denaturation.

Vegetables are consumed for various morphological parts. The classification is as follows:

• Root: Carrot, Radish, Beetroot, Turnip.
• Stem (Modified): Potato (Tuber), Colocasia (Corm), Ginger (Rhizome).
• Stem (Aerial): Asparagus, Kohlrabi (Knob).
• Bulb: Onion, Garlic.
• Leaf: Spinach, Lettuce, Amaranthus, Coriander.
• Flower / Inflorescence: Cauliflower (Curd), Broccoli (Head).
• Fruit (Immature): Okra, Cucumber, Brinjal, Beans, Peas.
• Fruit (Mature): Tomato, Watermelon, Muskmelon, Pumpkin.

Soil texture refers to the relative proportion of sand, silt, and clay particles in the soil mass.

1. Sandy Soil:

• Contains sand.
• Properties: Good drainage, good aeration, low water holding capacity, low nutrient retention.
• Suitability: Good for tuber and root crops (Carrot, Radish) as it allows root expansion without resistance. Also suitable for cucurbits and early vegetable production.

2. Clay Soil:

• Contains clay.
• Properties: Poor drainage, poor aeration, high water holding capacity, becomes hard when dry and sticky when wet.
• Suitability: Generally difficult to manage but good for Rice and certain leafy vegetables if drainage is improved.

3. Loam Soil:

• Balanced mixture of sand, silt, and clay.
• Properties: Ideal water holding capacity, drainage, and aeration.
• Suitability: Best soil for most fruit and vegetable crops (Mango, Banana, Tomato, etc.).

4. Silty Soil:

• Intermediate properties, high fertility but susceptible to compaction.

Flowering plants (Angiosperms) are divided into two classes based on the number of cotyledons in the seed.

1. Monocotyledons (Monocots):

• Seed: One cotyledon.
• Roots: Fibrous root system.
• Leaves: Parallel venation.
• Flowers: Floral parts usually in multiples of 3.
• Families & Examples:
  • Alliaceae: Onion, Garlic, Leek.
  • Araceae: Colocasia (Taro), Elephant foot yam.
  • Dioscoreaceae: Yams.
  • Musaceae: Banana (Plantain).

2. Dicotyledons (Dicots):

• Seed: Two cotyledons.
• Roots: Tap root system.
• Leaves: Reticulate (net-like) venation.
• Flowers: Floral parts in multiples of 4 or 5.
• Families & Examples:
  • Leguminosae: Peas, Beans.
  • Solanaceae: Potato, Tomato.
  • Cruciferae: Cabbage, Cauliflower.
  • Cucurbitaceae: Gourd vegetables.

Frost occurs when the temperature of the plant or the air surrounding it falls below , causing water within plant cells to freeze, leading to cell rupture and tissue death.

Types of Frost:

1. Radiation Frost: Occurs on calm, clear nights when heat radiates from the ground to the sky. The soil surface becomes colder than the air above it (Temperature Inversion).
2. Advective Frost: Caused by the influx of a cold air mass (cold wave) into an area with strong winds. Harder to protect against.

Protection Measures:

• Site Selection: Avoid planting in low-lying areas ("frost pockets") where cold air settles.
• Irrigation: Water has a high specific heat. Flooding the field releases latent heat () preventing temperature from dropping below freezing.
• Smudging: Burning waste material (straw, leaves) to create a smoke screen over the orchard reduces heat radiation loss to the sky.
• Wind Breaks: Planting tall trees (like Eucalyptus, Poplar) on the North-West boundary to block cold winds.
• Covering/Thatching: Covering young plants with straw or plastic sheets (leaving the south side open for sunlight).
• Heating: Using orchard heaters (expensive).

Fruit trees bear flowers and fruits on specific wood ages and positions. Understanding this is crucial for pruning.

1. Terminal Bearers:

• Flowers/Fruits appear at the tip of the current season's growth or past season's shoots.
• Examples: Mango (panicles are terminal), Loquat.

2. Axillary Bearers:

• Flowers/Fruits appear in the axils of leaves along the shoot.
• Examples: Guava, Fig, Jackfruit.

3. Spur Bearers:

• Fruits are borne on short, specialized, compressed shoots called spurs.
• Examples: Apple, Pear, Plum, Sweet Cherry.

4. Mixed Bearers:

• Bear on both terminal and axillary buds.
• Example: Pomegranate.

Family: Rutaceae (Citrus Family)

This family is highly significant in tropical and subtropical horticulture.

Characteristics:

• Plants are usually aromatic shrubs or trees due to the presence of oil glands.
• Leaves are often compound (unifoliate in Citrus).
• Fruit Type: Hesperidium (a modified berry with a leathery rind and juice sacs).
• Rich in Vitamin C.

Major Crops:

1. Sweet Orange: Citrus sinensis
2. Mandarin/Santra: Citrus reticulata
3. Acid Lime (Kagzi lime): Citrus aurantifolia
4. Lemon: Citrus limon
5. Grapefruit: Citrus paradisi
6. Wood Apple (Bael): Aegle marmelos

Soil salinity is determined by the Electrical Conductivity (EC) of the soil solution. Crops differ in their ability to tolerate salts.

1. Sensitive Crops:

• Yield decreases significantly even at low salinity levels ().
• Examples: Apple, Pear, Strawberry, Bean, Onion, Carrot, Citrus.

2. Moderately Tolerant Crops:

• Can withstand moderate salinity ().
• Examples: Grape, Pomegranate, Fig, Tomato, Cabbage, Cauliflower, Potato.

3. Highly Tolerant Crops:

• Can grow in high salinity soils (), sometimes up to .
• Examples: Date palm, Ber (Ziziphus mauritiana), Aonla, Coconut, Beetroot, Spinach.

1. Atmospheric Humidity:

• Fruit Quality: High humidity improves fruit skin texture (e.g., thin rind in citrus) but low humidity is better for fruit color development.
• Pests & Diseases: High humidity favors fungal diseases (powdery mildew, anthracnose) and insect pests. Low humidity during flowering causes desiccation of pollen grains leading to poor fruit set.
• Transpiration: High humidity reduces water loss from plants.

2. Rainfall:

• Source of Water: Essential for rain-fed horticulture.
• Timing: Rains during flowering wash away pollen (e.g., in Mango) and reduce pollinator activity. Rains during ripening cause fruit cracking (e.g., Cherry, Grape, Pomegranate) and spoilage.
• Excess Rain: Causes waterlogging, leading to root rot (e.g., in Papaya) and leaching of nutrients.
• Classification:
  • High water requirement: Banana ().
  • Low water requirement: Ber, Date Palm, Custard Apple.

Family: Rosaceae (Rose family)

This is the third most economically important plant family in temperate regions.

Characteristics:

• Flowers are usually showy, actinomorphic, and hermaphrodite.
• Stamens are numerous.
• Fruit types vary (Pome, Drupe, Aggregate).

Major Temperate Fruits:

1. Apple: Malus domestica (Fruit type: Pome).
2. Pear: Pyrus communis (Fruit type: Pome).
3. Peach: Prunus persica (Fruit type: Drupe/Stone fruit).
4. Plum: Prunus domestica (European) / Prunus salicina (Japanese) (Fruit type: Drupe).
5. Strawberry: Fragaria ananassa (Fruit type: Aggregate of achenes).
6. Almond: Prunus dulcis (Nut).

Plants are classified into different groups based on their adaptation to water availability:

1. Hydrophytes:

• Plants adapted to grow in water or very wet soils.
• Examples: Water chestnut (Trapa natans), Lotus (Nelumbo nucifera).

2. Mesophytes:

• Plants adapted to moderate water conditions (neither too wet nor too dry). Most horticultural crops fall into this category.
• Examples: Mango, Apple, Tomato, Potato, Rose.

3. Xerophytes:

• Plants adapted to dry or arid conditions (Water scarcity). They have modifications like thick cuticle, sunken stomata, or thorns to reduce transpiration.
• Examples: Ber (Ziziphus), Date palm, Prickly pear (Cactus), Aloe vera.

1. Management of Acidic Soils ():

• Liming: Application of Calcium Carbonate (), Dolomite, or Quick lime. It neutralizes acidity and supplies Ca/Mg.
• Rock Phosphate: Use as a source of Phosphorus instead of superphosphate.
• Acid Tolerant Crops: Growing crops like Pineapple, Potato, Sweet Potato, or Tea.

2. Management of Sodic/Alkali Soils (High ESP, High pH ):

• Gypsum Application: Application of Gypsum (). Calcium replaces Sodium on the soil exchange complex, allowing Sodium to leach out as Sodium Sulphate.
  
• Iron Pyrites: Can be used to reclaim alkali soils.
• Green Manuring: Incorporating Dhaincha (Sesbania aculeata) adds acidity during decomposition.
• Tolerant Crops: Growing Ber, Date palm, Aonla.

Comprehensive Classification of Mango:

• Common Name: Mango (King of Fruits / National Fruit of India).
• Botanical Name: Mangifera indica L.
• Family: Anacardiaceae.
• Chromosome Number: (Allopolyploid/Amphidiploid).

Classifications:

1. Life Span: Perennial (Tree).
2. Climatic Zone: Tropical (requires warm temperature), but widely grown in Sub-tropics.
3. Leaf Shedding: Evergreen.
4. Ripening Behavior: Climacteric (ripens after harvest).
5. Photoperiodism: Day Neutral.
6. Fruit Type: Drupe (Stone fruit).
7. Edible Part: Mesocarp.
8. Bearing Habit: Terminal bearer.