Fruit Classification

Fruit: Definition and Fundamental Components

  • Fruit: Matured or ripened ovary with or without accessory parts.

  • Uses: can be consumed raw; can be canned or processed.

Detailed Fruit Structure

Pericarp: The Fruit Wall

  • Pericarp = outer wall of the maturing ovary that becomes the wall of the fruit.

  • Pericarp can be either dry or fleshy.

  • Three layers:

    • Exocarp: outermost layer (skin of the fruit) ext{Exocarp}

    • Mesocarp: middle layer, can be fleshy and edible ext{Mesocarp}

    • Endocarp: innermost layer that surrounds the seed ext{Endocarp}

Seed: Structure and Function

  • Ovules mature into seeds.

  • Seeds protect and nourish the embryo and enable production of new plants.

  • Seed components:

    • Seed Coat

    • Embryo

    • Stored Food

Botanical Classification of Fruits (Morphology)

Ovary Position

  • Ovaries can be positioned on the thalamus in three ways:

    • Superior ovary: Ovary is at the highest position on the thalamus; petals, calyx, and stamens are positioned below the ovary.

      • Examples: ext{citrus}, ext{brassica (mustard)}

    • Half-inferior ovary: Thalamus forms a cup-like shape around the ovary; petals, calyx, and stamens are situated along the rim of the cup.

      • Examples: ext{rose}, ext{prunus}

    • Inferior ovary: Thalamus completely covers the ovary; petals, calyx, and stamens are located near the top of the ovary.

      • Examples: ext{cucurbits}, ext{apple}

Carpel Structure

  • Carpel: Female reproductive part of the flower, consisting of stigma, style, and ovary.

  • Flowers can have a single carpel (monocarpellary gynoecium) or multiple carpels (multicarpellary gynoecium).

  • Compound or Multicarpellary Gynoecium (more than one carpel present):

    • Apocarpous: each carpel is isolated, forming separate gynoecia.

    • Syncarpous: carpels are fused to form a single compound gynoecium.

Locules

  • Locules: Chambers present in the ovary.

  • Fruits can be unilocular (single locule) or multilocular (multiple locules).

  • Ovules (which later form seeds) are present in locules.

Classification by Number of Ovaries Involved in Fruit Formation

  • Fruits are classified into three groups:

    • A. Simple fruit

    • B. Aggregate fruit

    • C. Multiple or composite fruit

A. Simple Fruit

  • A single or compound ovary of a flower has matured into a simple fruit.

  • Examples: ext{banana}, ext{cherry}, ext{apple}, ext{etc.}

  • Based on maturity of the pericarp, simple fruits are divided into two broad groups:

    • I. Fleshy fruits

    • II. Dry fruits

I. Fleshy Fruits

  • Pericarp becomes fleshy and succulent at maturity.

  • Pericarp is divided into three layers: Epicarp / Exocarp, Mesocarp, Endocarp.

  • Fleshy fruits are classified as:

    1. Berries

    2. Drupes

    3. Pomes

    4. Hesperidium

    5. Pepo

1. Berries

  • Developed from a single flower with a single or fused multiple carpels.

  • Fruit has succulent pericarp and multiple seeds.

  • Pericarp parts: thin exocarp; undifferentiated mesocarp and endocarp.

  • Seeds are embedded in the pulp.

  • Examples: ext{tomato}, ext{grape}, ext{blueberry}

  • Note: Strawberry, Raspberry, and Blackberry are not true berries botanically.

2. Drupes (stone fruits)

  • Developed from a single flower with a Superior ovary.

  • Usually a single carpel with 1 or 2 seeds.

  • Exocarp thin; Mesocarp fleshy and pulpy; Endocarp hard and stony.

  • Examples: ext{peach}, ext{plum}, ext{cherry}, ext{apricot}, ext{mango}, ext{almond}

  • Exceptions: coconut has a fibrous mesocarp and a hard endocarp; almond shows a hard endocarp as well.

3. Pomes

  • Developed from a compound syncarpous inferior ovary.

  • Accessory tissue or flower parts become fleshy along with the ovary to form the fruit.

  • Not a true fruit since the fruit is developed from accessory tissue; the central part (core) is the true fruit.

  • Pericarp layers: Exocarp and Mesocarp are fleshy; Endocarp is cartilaginous or stony.

  • Examples: ext{apple}, ext{pear}, ext{quince}

4. Hesperidium

  • Developed from a multilocular, syncarpous, and superior ovary.

  • Exocarp is leathery and contains volatile aromatic oil glands.

  • Exocarp and Mesocarp form the covering of the fruit.

  • Each section corresponds to one carpel.

  • Interior of the carpels contains juice-filled vesicles (specialized trichomes).

  • Examples: ext{orange}, ext{lemon}, ext{grapefruits} (all citrus)

5. Pepo

  • Developed from one carpel or fused multiple carpels in an inferior ovary.

  • Exocarp is woody or leathery; Mesocarp is fleshy; generally many seeds.

  • Examples: ext{zucchini}, ext{cucumber}, ext{squash}

Accessory Fruits (General Concept)

  • Fruits formed by involvement of accessory floral parts along with the ovary wall.

  • Example: Strawberry is not a true fruit by botanical definition (receptacle tissue along with ovary wall forms the strawberry); other examples include ext{cashew apple}, ext{figs}.

II. Dry Fruits

  • Pericarp becomes hard or brittle with very low moisture content.

  • Pericarp is not differentiated into Exocarp, Mesocarp, Endocarp.

  • Two types:

Dry Dehiscent Fruits

  • Pericarp opens at maturity along the sutures to release seeds.

  • Examples: ext{legumes (bean, pea)}, ext{brassica (mustard)}

Dry Indehiscent Fruits

  • Pericarp does not split open at maturity.

  • Examples: ext{nuts (chestnut, hazelnut)}

  • Note: Question in transcript asks which type of dry fruits are easier to manage (harvest when labor is available).

B. Aggregate Fruit

  • Develop from multiple ovaries of the same flower (apocarpous type).

  • Each ovary can form a small berry or drupe-type fruitlet.

  • After fertilization, each ovary retains one ovule that matures into a seed.

  • Examples: ext{raspberry}, ext{blackberry}, ext{strawberry}

C. Multiple (Composite) Fruit

  • Develop from an entire inflorescence.

  • Many flowers densely packed in an inflorescence each produce small fruitlets.

  • These fruitlets mature into a single mass of fruit.

  • Examples: ext{pineapple}, ext{mulberry}, ext{fig}, ext{jackfruit}

Other Classifications

Classification of Fruits Based on Climatic Region

  • Temperate zone fruit plants:

    • Dormancy occurs in Fall/late Summer.

    • Require a certain number of freeze hours to break dormancy and resume growth in Spring.

    • Tolerant to freeze/frost.

    • Examples: ext{apple}, ext{pear}, ext{peach}, ext{cherries}

  • Subtropical zone fruit plants:

    • Temperature milder than temperate crops.

    • Moderately tolerant to chilling for brief spells; chilling can aid production.

    • Sensitive to frost.

    • Do not have a definite dormancy period or freeze-hour requirement.

    • Examples: ext{avocado}, ext{citrus}, ext{olives}

  • Tropical zone fruit plants:

    • Require high temperature; not tolerant to freezing.

    • Perform well in hot, humid conditions.

    • Diurnal temperature variation is narrow.

    • Examples: ext{mango}, ext{jackfruit}

Classification Based on Ripening Behavior

  • At ripening, fruits attain desirable flavor, sweetness, texture, and color.

  • Two groups:
    1) Climacteric fruits
    2) Non-climacteric fruits

1. Climacteric Fruits

  • Continue ripening after harvest.

  • Harvest at fully mature stage but not fully ripened.

  • After ripening, fruits become soft and delicate and are difficult to transport, so transport is usually done at the mature stage.

  • After harvest, they emit a higher amount of ethylene and have an increased respiration rate, which enhances ripening.

  • Ethylene can be applied in closed environments to induce ripening.

  • Examples: ext{mango}, ext{banana}, ext{papaya}, ext{pear}, ext{apple}

2. Non-climacteric Fruits

  • Do not ripen after harvest.

  • Produce very little ethylene.

  • Do not respond to ethylene treatments for ripening.

  • No significant increase in respiration rate.

  • Examples: ext{citrus}, ext{strawberry}, ext{cherries}

Climacteric vs. Non-climacteric Respiration Pattern

  • Climacteric: CO₂ production shows a pre-climacteric minimum, a climacteric peak, then a post-climacteric decline.

  • Non-climacteric: CO₂ production pattern remains relatively steady without a pronounced peak.

  • Source: Salveit, ext{2004}

Classification Based on Photoperiodism

  • Photoperiodism: Developmental response of plants to the relative length of light and dark periods.

  • Example: photoperiod of 14 ext{ hours} means 14 ext{ hours} of light and 10 ext{ hours} of darkness.

  • Three types:

    • Short-day plants (long-night plants)

    • Long-day plants (short-night plants)

    • Day-neutral plants

Short-day Plants (Long-night plants)

  • Flower when daylength is shorter than a critical value (longer dark period).

  • Also known as long-night plants.

  • Examples: ext{strawberry}, ext{pineapple}

Long-day Plants (Short-night plants)

  • Flower when daylength is longer than a critical value (shorter dark period).

  • Also known as short-night plants.

  • Examples: ext{banana}, ext{apple}

  • Note: Apple flowers when day length exceeds roughly 12 ext{-}14 ext{ hours}

Day-neutral Plants

  • Do not require a definite light or dark period to flower.

  • Flower after a certain period of growth and development.

  • Example: ext{papaya}

Question (from transcript): What type is most desirable among the following?

  • Short-day plants

  • Long-day plants

  • Day-neutral plants

Overview: Simple, Aggregate, Multiple Fruits (Summary)

  • Simple fruit

  • Aggregate fruit

  • Multiple (composite) fruit