Unfruitfulness in Horticultural Crops

1. Introduction

• The ultimate goal of fruit cultivation is to achieve maximum fruit set and yield.
  However, in many fruit crops, plants flower profusely but fail to set fruits or retain them till maturity.
• This condition is known as unfruitfulness.
  It is one of the most serious physiological problems in fruit production, leading to low yields, economic losses, and reduced orchard profitability.

2. Definition

• Unfruitfulness is the condition in which a plant fails to set fruits or the fruits drop prematurely, even though flowering has occurred.
• It may be due to internal (genetic/physiological) or external (environmental/cultural) factors that interfere with pollination, fertilization, or fruit development.

3. Types of Unfruitfulness

Unfruitfulness can be classified into two main types:

• Primary (Inherent / Genetic) Unfruitfulness; This type of unfruitfulness is naturally present in the plant due to its genetic makeup or reproductive biology.

1. Juvenility: Young plants (especially seedlings) are incapable of flowering or fruiting even under favorable conditions. Example: Seedling mango trees may take 6–8 years to bear. Grafted plants (using mature scions) fruit earlier. Remedy: Use vegetatively propagated plants or precocious rootstocks.
2. Genetic Sterility: The reproductive organs (pollen or ovule) are non-functional or abortive, leading to failure of fertilization. Example: Banana and Seedless grapes are naturally sterile. Remedy: Use parthenocarpic (seedless) or vegetatively propagated varieties.
3. Incompatibility: Failure of fertilization even after pollination due to pollen–pistil incompatibility (physiological or genetic). Common in cross-pollinated fruit crops.

Remedy:

• Plant compatible pollinizer varieties.
• Introduce beehives for effective pollination.

4. Dichogamy: Difference in timing between pollen release (anther dehiscence) and stigma receptivity, leading to reduced fertilization.

Remedy: Plant varieties with overlapping flowering periods. Ensure presence of pollinizer trees.

5. Sex Expression Abnormalities: Some crops produce more male than female flowers, leading to poor fruit set. Common in dioecious or monoecious plants.

6. Parthenocarpy: Development of fruit without fertilization (seedless fruits). Can be natural or induced.

Though parthenocarpy produces seedless fruits, it is sometimes considered a form of unfruitfulness because fertilization does not occur.

7. Embryo Abortion: Fertilization occurs, but the embryo fails to develop due to genetic or physiological disturbances. Example: Litchi, Apple, and Pear sometimes experience embryo abortion. Remedy: Balanced nutrition and adequate irrigation during fruit set period.

 II. Secondary (Environmental / Cultural) Unfruitfulness

This type is caused by unfavorable environmental conditions, deficient cultural practices, or management errors.

1. Temperature Extremes

• High or low temperature affects:
  • Pollen viability and germination.
  • Stigma receptivity.
  • Ovule development.

Remedy: Avoid off-season flowering. Use protective structures or windbreaks.

2. Water Stress

• Drought or excess moisture during flowering and fruit set reduces fertilization.
• Causes flower and fruit drop in mango, citrus, and papaya.

Remedy: Provide timely irrigation and proper drainage.

3. Nutritional Imbalance

• Deficiency of nutrients, especially Phosphorus (P), Potassium (K), Boron (B), and Zinc (Zn), leads to:
  • Poor pollen germination.
  • Weak fruit set.
  • Premature fruit drop.

Remedy: Apply balanced fertilizer doses based on soil and leaf analysis. Use Boron (0.1%) and Zinc sulphate (0.5%) foliar sprays.

4. Lack of Pollinators: Insects, especially bees, play a vital role in cross-pollination. Absence of pollinators leads to unfruitfulness in apple, pear, and citrus. Remedy: Introduce beehives (2–3 per hectare) during flowering. Avoid pesticide sprays during bloom.

5. Pests and Diseases: Attack on flowers or developing fruits reduces fruit set. Example: Mango hopper, thrips, and powdery mildew cause flower drop in mango. Remedy: Adopt Integrated Pest and Disease Management (IPDM) practices.

6. Hormonal Imbalance: High levels of Gibberellins (GA) promote vegetative growth and inhibit flowering. Low cytokinin and ABA levels also reduce fruit set.

Remedy:

• Use growth regulators such as:
  • Paclobutrazol (5–10 ml/tree) – to induce flowering in mango.
  • NAA (20–40 ppm) – to reduce fruit drop.
  • 2,4-D (10 ppm) – to improve fruit retention.

7. Alternate Bearing: In some fruit crops, heavy fruiting one year exhausts the tree, causing poor flowering in the next. Common in mango, apple, and citrus. Remedy: Regular pruning, thinning, and balanced nutrition. Use of Paclobutrazol to regulate flowering.

8. Improper Orchard Management: Poor spacing, excessive shade, improper pruning, and lack of sanitation may lead to poor flowering and fruit set. Remedy: Maintain proper spacing and canopy structure. Adopt regular pruning, irrigation, and fertilization schedules.

• Role of Growth Regulators in Preventing Unfruitfulness

• Examples of Unfruitfulness in Major Fruit Crops