Unfruitfulness:

In an orchard, the inability of some fruit trees to flower, set fruit, or bear fruits regularly, despite similar conditions, is referred to as unfruitfulness. Understanding its causes is essential for effective control and achieving economically acceptable production levels. Below are key concepts and the classification of factors causing unfruitfulness:

Unfruitfulness refers to the failure of fruit trees in an orchard to flower, set fruits, or mature fruits under similar conditions where other trees may perform well. This issue can arise due to a variety of reasons, both internal and external.

Key Concepts Related to Unfruitfulness

1. Fruit Setting: The initial growth of the ovary and associated parts post-blossoming, culminating in maturity.
2. Fruitfulness: The plant’s capability to flower, set fruit, and mature fruits.
3. Infertility: The plant’s ability to produce fruits with viable seeds. Inability leads to sterility. All fertile plants are fruitful, but not all fruitful plants are fertile (e.g., seedless fruits).
4. Self Fruitfulness: The ability of a plant to mature fruits post-self-pollination.
5. Self Fertility: The plant’s capacity to produce viable seeds post-self-pollination.

Factors Causing Unfruitfulness

A) Internal Factors

These factors originate within the plant and are broadly categorized into evolutionary tendencies, genetic influences, and physiological factors.

1. Evolutionary Tendencies

• Monoecious and Dioecious Nature:
  • Monoecious Plants: Stamens and carpels in different flowers on the same plant. Generally, pollination and fruit set are not a problem (e.g., Coconut, Arecanut). However, pollinators may need to be ensured.
  • Dioecious Plants: Male and female flowers on separate plants. Examples include Papaya, Date Palm, and Strawberry. Lack of pollinators can lead to unfruitfulness.

• Heterostyly:
  • In flowers where the style’s length varies among plants, self-pollination is often hindered.
  • Example: In Brinjal, styles are categorized into four types. Flowers with pseudo-short and true-short styles fail to produce fruits.

• Dichogamy:
  • Occurs in monoecious plants when the stigmatic receptivity does not coincide with pollen viability.
    • Protandry: Stamens mature before the stigmas (e.g., Coconut varieties).
    • Protogyny: Stigmas become receptive before stamens produce viable pollen (e.g., Walnuts, Hazels).

• Abortive Flowers or Pistils:
  • Developmental failure of flowers, pistils, or stigmas leads to fruit set failure.
  • Examples:
    • Grapes and Tomatoes produce sterile late flowers.
    • Certain olive varieties experience 10-60% abortive embryos.

• Impotence of Pollen:
  • Some plants produce non-viable pollen despite having perfect flowers.
  • Examples:
    • Sterility in grapes due to degeneration of the generative nucleus.
    • Sterile pollen is common in J.H. Hale Peach, Washington Navel Orange, and Tahiti Lime.

Genetic and Physiological Influences on Sterility and Unfruitfulness

Genetic Influences

1. Self-Sterility:

• • Determined by inheritance but may develop under favorable environmental conditions.
  • Affects both offspring and hybrids.

2. Sterility and Unfruitfulness Due to Hybridity:

• • Extent of Crossing: Wider crosses tend to result in higher sterility levels. Examples include:
    • Cross between peach and plum: Abundant flowers but no pistils and malformed stamens.
    • Hybrid between pear and quince: Seedless fruit.
    • Most Citranges (sweet orange × Citrus trifoliata): No fertile female gametes.
    • Seedlessness in bananas and pineapples: Attributed to hybrid nature of ancestors.
    • Triploid apple varieties: Produce aborted pollen.
    • Hybrids between Vitis rotundifolia and Euvitis: Completely sterile.
    • Similar results with Vitis vinifera × Vitis rotundifolia.

3. Incompatibility:

• • Common cause of self-unfruitfulness.
  • Pollen and ovules are fertile but fail to conjugate.
  • Examples include:
    • Apple, pear, plum, and aonla: Require pollinizer varieties for fruit setting.
    • Mango varieties (Langra, Dashehari, Chausa): Exhibit self-incompatibility.
    • Other crops like almond, apricot, and Clementine mandarins: Fertilization fails due to incompatibility despite functional gametes.

Physiological Influences

1. Slow Pollen Tube Growth:

• • Results in unfruitfulness due to chemotropic or hormonal influences.
  • Differences observed in selfed vs. crossed fruits (apples, pears, cherries, citrus).
  • Fertilization delay can lead to abscission at the base of style, ovary, pedicel, or peduncle.

2. Premature or Delayed Pollination:

• • Premature Pollination:
    • Immature pistils cannot support fertilization, leading to flower fall.
    • Examples: Lower fruit setting in persimmon, pear, plum, and peach.
    • No harmful effects in oranges; minor injury noticed in tomatoes.
  • Delayed Pollination:
    • Flowers fall without setting if pollination is excessively delayed.
    • Delays of 1–2 days do not affect fruit set but may result in polyembryonic seeds in some species.

3. Nutritive Condition of the Plant:

• • Critical during and around the blossoming period, influencing flower retention, pollen viability, and pistil fertility.
  • Pollen Viability:
    • Significant differences observed in pollen germination between old and young apple trees of the same variety.
  • Defective Pistils:
    • Caused by overbearing, drought, or nutrient-poor soils.
    • Results in unfruitfulness (e.g., American plums, Vitis vinifera).
    • Carbohydrate deficiency in Vitis vinifera and greenhouse tomatoes leads to flower abortion.

4. Flower Position and Fruit Setting:

• • Positional competition influences fruit set.
  • Fruits on terminal growth have a smaller set percentage due to higher competition for nutrients.

5. Spur Strength and Fruit Setting:

• • Strong spurs on vigorous limbs with larger leaves set more fruits than weak limbs.
  • Flowers borne singly are more likely to mature compared to those in clusters, which often drop.

6. Girdling or Ringing: Promotes accumulation of food reserves, enhancing fruit set and sometimes leading to parthenocarpy.

7. Nutritional Deficiencies:

• • Insufficient nutrients diminish seed-forming ovules and fruit wall development.
  • Severe deficiencies result in aborted growth of flowers and fruits.
  • Examples:
    • Greenhouse cucumbers: Growth arrested in certain fruits based on position and pollination timing; remaining fruits resume growth after some are harvested.
    • Strawberries: Bisexual flowers may produce pistillate flowers under nutrient stress.

8. Nutritional Influence on Compatibility: Indirect effect; poor nutritional conditions can exacerbate compatibility issues.

B. Unfruitfulness Associated with External Factors

1. Nutrient Supply

• In families like Graminae, Cruciferae, and Leguminaceae, sterility can occur due to overfeeding.
• Example:
  • Jonathan apple, which is self-sterile in rich soil, becomes self-fertile in poor soils.
  • In grapes, high fertility leads to good pistil development, while low fertility results in poor pistil and good stamen development.
  • In olives, low fertility may lead to partial or complete degeneration of pistils.

2. Pruning and Training

• Proper pruning promotes the development of true hermaphrodite flowers in certain grape varieties (e.g., Hope).
• Lack of pruning leads to sterility and the production of aborted pistils.

3. Locality

• Some crops exhibit different fertility behaviors depending on the location.
  • Example: Jonathan apple is sterile in one location but self-fertile in another.

4. Season

• Certain hybrid varieties show seasonal fertility differences.
  • Example: Hybrid grape Ideal is self-impotent early in the season but becomes self-potent later.

5. Temperature

• High temperatures at flowering can dry up stigmatic secretions, preventing pollination.
  • Example: Tomato varieties grown at high temperatures often fail to set fruit.

6. Light

• Exposure to long photoperiods influences flower development.
  • Example: In strawberries, long photoperiods result in the development of both stamens and pistils.

7. Pests and Diseases

• Pests like the mango hopper and diseases like powdery mildew reduce fruit set and development in mango and grape.
• Fungicide sprays during flowering can inhibit fruit set.
  • Example: Copper fungicides (200 to 10,000 ppm) prevent pollen germination on the stigma.

Steps to Overcome Unfruitfulness

To address unfruitfulness effectively, corrective measures should begin at the planning stage and extend to managing an established orchard:

Crop and Variety Selection Choose crops and varieties suitable for the climatic and soil conditions of the site.

Windbreaks and Shelterbelts Provide wind protection in areas prone to wind damage.

Soil Optimization Prepare the soil by incorporating organic matter, amendments, and nutrients based on soil analysis.

Pollination Management Address issues like heterostyly, dichogamy, incompatibility, sterility, and embryo abortion by:

• • Growing a mixture of varieties.
  • Introducing effective pollinizer varieties.
  • Utilizing pollinators like honeybees.

Use of Plant Regulators Apply plant growth regulators after standardizing chemical concentration and timing to address problems like slow pollen tube growth and premature/delayed pollination.

Rejuvenation of Old Trees Replant or rejuvenate old trees to overcome age-related issues.

Managing Overbearing Thin fruits at appropriate stages to reduce overbearing and ensure balanced fruit set.

Irrigation Management Manage water supply effectively, especially in drought-prone or waterlogged areas.

Flower Distribution and Crop Regulation Address uneven flower distribution through thinning and crop regulation.