Types and Mechanisms of Action of Common Agents for Flower and Fruit Preservation in Vegetables
(I) Plant Growth Regulators
1. Auxins
(2,4-D), 4-CPA. These agents function by mimicking endogenous plant auxins, thereby promoting cell elongation and division, enhancing metabolic activity within the ovary, and inducing parthenocarpy (seedless fruit formation). 2,4-D exhibits high biological activity and is frequently used for solanaceous vegetables such as tomatoes and eggplants; however, its application concentration must be strictly controlled (typically 10–20 mg/L for tomatoes), as excessive concentrations can easily lead to fruit malformation. 4-CPA offers a higher safety profile and is suitable for use on a wide variety of vegetables, including tomatoes, cucumbers, and peppers, typically at concentrations ranging from 25 to 50 mg/L.
2. Gibberellins
Gibberellic Acid (GA3) promotes cell elongation and breaks dormancy, thereby significantly increasing the fruit-setting rate. In grape cultivation, applying GA3 (50 mg/L) during the flowering stage can promote berry enlargement and reduce stem lignification (hardening of the fruit stalk). For strawberries, spraying GA3 (5–10 mg/L) during the flowering stage accelerates peduncle elongation and improves pollination efficiency.
3. Cytokinins
Examples include 6-Benzylaminopurine (6-BA) and Forchlorfenuron (KT-30). These agents promote cell division, delay senescence, and increase the total number of cells within the fruit. Forchlorfenuron is widely applied to watermelons and melons, where it significantly promotes fruit enlargement; however, improper application can easily result in hollow centers or malformations within the fruit.
(II) Nutritional Elements
1. Boron Fertilizers
Boron plays a crucial role in the synthesis of pectin substances within plant cell walls and promotes pollen germination and pollen tube elongation. Boron deficiency leads to poor development of floral organs and reduced pollen viability in vegetables, subsequently causing flower and fruit drop. Spraying a 0.1%–0.2% solution of borax or boric acid during the flowering stage can significantly increase the fruit-setting rates of vegetables such as tomatoes, cucumbers, and legumes.
2. Calcium Fertilizers
Calcium stabilizes cell membrane structures and enhances both fruit firmness and stress resistance. Physiological disorders—such as blossom-end rot in tomatoes and peppers—are closely linked to calcium deficiency. Foliar application of a 0.3%–0.5% calcium chloride or calcium sugar alcohol solution during the fruiting stage can effectively prevent such diseases and extend the fruit's shelf life.
3. Phosphorus and Potassium Fertilizers
Phosphorus participates in plant energy metabolism and promotes flower bud differentiation; potassium enhances the plant's stress resistance and improves the efficiency of transporting photosynthetic products to the fruit. Foliar application of a 0.2%–0.3% monopotassium phosphate solution can significantly boost the flowering and fruit-setting capabilities of vegetables.
(III) Biostimulants
1. Seaweed Extracts
Rich in active substances such as polysaccharides, phenolic compounds, and plant growth regulators, these extracts enhance plant stress resistance and promote flower bud differentiation and fruit development. Studies have shown that applying a foliar fertilizer containing alginic acid during the cucumber flowering stage can increase the fruit-setting rate by 15%–20%.
2. Humic Acids
These compounds improve soil structure, promote root development, and enhance the plant's capacity for nutrient uptake. Additionally, humic acids regulate the balance of endogenous plant hormones, thereby improving the retention of flowers and fruits in vegetable crops.
1. Auxins
(2,4-D), 4-CPA. These agents function by mimicking endogenous plant auxins, thereby promoting cell elongation and division, enhancing metabolic activity within the ovary, and inducing parthenocarpy (seedless fruit formation). 2,4-D exhibits high biological activity and is frequently used for solanaceous vegetables such as tomatoes and eggplants; however, its application concentration must be strictly controlled (typically 10–20 mg/L for tomatoes), as excessive concentrations can easily lead to fruit malformation. 4-CPA offers a higher safety profile and is suitable for use on a wide variety of vegetables, including tomatoes, cucumbers, and peppers, typically at concentrations ranging from 25 to 50 mg/L.
2. Gibberellins
Gibberellic Acid (GA3) promotes cell elongation and breaks dormancy, thereby significantly increasing the fruit-setting rate. In grape cultivation, applying GA3 (50 mg/L) during the flowering stage can promote berry enlargement and reduce stem lignification (hardening of the fruit stalk). For strawberries, spraying GA3 (5–10 mg/L) during the flowering stage accelerates peduncle elongation and improves pollination efficiency.
3. Cytokinins
Examples include 6-Benzylaminopurine (6-BA) and Forchlorfenuron (KT-30). These agents promote cell division, delay senescence, and increase the total number of cells within the fruit. Forchlorfenuron is widely applied to watermelons and melons, where it significantly promotes fruit enlargement; however, improper application can easily result in hollow centers or malformations within the fruit.
(II) Nutritional Elements
1. Boron Fertilizers
Boron plays a crucial role in the synthesis of pectin substances within plant cell walls and promotes pollen germination and pollen tube elongation. Boron deficiency leads to poor development of floral organs and reduced pollen viability in vegetables, subsequently causing flower and fruit drop. Spraying a 0.1%–0.2% solution of borax or boric acid during the flowering stage can significantly increase the fruit-setting rates of vegetables such as tomatoes, cucumbers, and legumes.
2. Calcium Fertilizers
Calcium stabilizes cell membrane structures and enhances both fruit firmness and stress resistance. Physiological disorders—such as blossom-end rot in tomatoes and peppers—are closely linked to calcium deficiency. Foliar application of a 0.3%–0.5% calcium chloride or calcium sugar alcohol solution during the fruiting stage can effectively prevent such diseases and extend the fruit's shelf life.
3. Phosphorus and Potassium Fertilizers
Phosphorus participates in plant energy metabolism and promotes flower bud differentiation; potassium enhances the plant's stress resistance and improves the efficiency of transporting photosynthetic products to the fruit. Foliar application of a 0.2%–0.3% monopotassium phosphate solution can significantly boost the flowering and fruit-setting capabilities of vegetables.
(III) Biostimulants
1. Seaweed Extracts
Rich in active substances such as polysaccharides, phenolic compounds, and plant growth regulators, these extracts enhance plant stress resistance and promote flower bud differentiation and fruit development. Studies have shown that applying a foliar fertilizer containing alginic acid during the cucumber flowering stage can increase the fruit-setting rate by 15%–20%.
2. Humic Acids
These compounds improve soil structure, promote root development, and enhance the plant's capacity for nutrient uptake. Additionally, humic acids regulate the balance of endogenous plant hormones, thereby improving the retention of flowers and fruits in vegetable crops.
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