Plant growth regulators (PGRs) are powerful tools in horticulture, offering a range of benefits from enhancing root development to extending the lifespan of cut flowers. These synthetic compounds mimic natural plant hormones and can significantly influence the growth and development of plants. By applying PGRs such as auxins, gibberellins, and cytokinins, gardeners and commercial growers can improve the health, aesthetics, and productivity of their floral crops.
One of the primary applications of PGRs is to promote rooting, which is crucial for the propagation of many ornamental plants. Auxins, such as naphthalene acetic acid (NAA) and indole-3-acetic acid (IAA), are commonly used to stimulate root formation in cuttings. For instance, research has shown that dipping the base of camellia cuttings in a 1000 µg/g NAA solution for 3-5 seconds can double the rooting rate within 50 days compared to untreated controls. Similarly, magnolia twigs soaked overnight in a 200 µg/g NAA solution exhibit improved rooting and survival rates.
A wide array of flowers, including jasmine, bougainvillea, and carnations, have shown positive responses to auxin treatments, leading to more successful rooting. This practice is particularly beneficial for species that are otherwise difficult to propagate.
Many perennial flowers have a natural dormancy period that must be overcome to initiate earlier blooming. Gibberellins, another class of PGRs, are effective in breaking seed dormancy and encouraging sprouting. For example, coating peony buds with a 500-1000 µg/g gibberellin solution or soaking Gloxinia seeds in a 25 µg/g gibberellin solution can significantly hasten germination and flowering.
To improve the ornamental appeal of flowers, PGRs like chlormequat chloride and daminozide are used to create compact, bushier plants with more abundant blooms. Geraniums treated with 500 µg/g of chlormequat chloride in the soil can flower up to two weeks earlier and exhibit a 10 cm reduction in height. Dahlias and chrysanthemums show pronounced dwarfing effects when treated with daminozide. Paclobutrazol is another PGR that can induce dwarfing in flowers like potted chrysanthemums, leading to shorter growth, denser foliage, and larger blooms.
The longevity of cut flowers is a key concern for both florists and consumers. Applying growth retardants can slow down the respiration rate of flowers, thereby extending their vase life. For instance, soaking the base of carnation stems in chlormequat chloride can prolong their freshness by 2-3 days. The optimal concentration for this treatment varies with the season, ranging from 50 µg/g in summer to 10-25 µg/g in winter.
PGRs like gibberellin, daminozide, and NAA can also be used to prevent premature fruit drop in ornamental fruit-bearing plants. Spraying leaves with a 50 µg/g NAA solution can reduce fruit fall. For potted kumquats and calamondins, a 15-20 µg/g gibberellin solution can inhibit fruit differentiation and prevent dropping. Asparagus benefits from a 10 µg/g NAA solution sprayed post-flowering to minimize fruit loss.
In seedless grape cultivation, gibberellin plays a crucial role in promoting fruit development and reducing seed formation. Spraying young grape clusters with a 200 µg/g gibberellin solution can enhance the size of seedless grapes, increase sugar content, and advance maturity by 1-2 weeks. Additionally, daminozide treatments before and after flowering can increase fruit set rates by over 30%.
The strategic use of PGRs in flower cultivation can lead to remarkable improvements in plant health, aesthetics, and productivity. By understanding and applying these regulators, growers can achieve specific cultivation goals, from propagating difficult-to-root species to extending the display of cut flowers.
For more detailed information on the use of plant growth regulators in horticulture, visit authoritative sources such as the American Society for Horticultural Science or the International Plant Propagators' Society.
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