Plant Growth Regulators (Lecture 10)

Plant Growth Retardants (GR)

• Synthetic organic compounds that cause retardation/inhibition of cell division and/or elongation
• Produce no significant growth defects/malformations
• Have little effect on the production of leaves or on root growth
• Reduce stem elongation, increase green color of leaves
• Block specific sites in pathways of PGR biosynthesis, especially Gibberellins biosynthesis

Gibberellins Biosynthetic Pathway

• Gibberellins are affected by GR
• GR inhibits key steps in GA biosynthesis

Sterols

• An essential component of cell membranes
• Plants and animals produce sterols
• Cholesterol is exclusively an animal sterol
• Plant sterols (phytosterols) are different, with 40 identified, including sitosterols, campestrols, and stigmasterols
• Plant sterols lower serum concentration of cholesterol

Use of Plant Growth Retardants

• Reduce plant height, especially in floricultural crops
• Examples of GR: ancymidol, chlomequat, daminozide, flurprimidol, mefluidide, paclobutrazol, tetcyclacis, and unicozole
• Used to manipulate size, shape, and overall quality of plants

Specific Applications

Floricultural Crops

• Poinsettia: Chlormequat chloride, CCC, is most effective in reducing height
• Chrysanthemum: Daminozide, Ancymidol, and Paclobutrazol are used to reduce height and improve quality
• Easter Lily: Ancymidol, Paclobutrazol, and Triademefon are used to reduce height

Bedding Plants

• Zinnia and Geranium: Daminozide and Paclobutrazol are used to control height

Turf Grass

• GRs are used to control growth, especially in difficult-to-maintain areas
• Examples of GRs: Chlorflurenol, Paclobutrazol, Melfluidide

Fruit Production

• Daminozide advances anthocyanin production in fruit skin and flesh in sweet cherry
• Daminozide increases anthocyanin synthesis, decreases fruit drop, and reduces fruit softening during cold storage in apples

Flower Bud Formation

• Daminozide stimulates flowering in apples and pears

Tree Size

• Paclobutrazol is effective for controlling shoot elongation in fruit trees

Lodging Control

• Chlormequat chloride reduces stem height and diameter, leading to increased yield in wheat, barley, and rye

Fruit Set

• Chlormequat chloride increases fruit set in grapes

Other Miscellaneous GR

• Maleic hydrazide prevents bud sprouting in onion and potatoes
• Citrus abscision agents induce abscision in citrus for mechanical harvesting

Application of Plant Growth Retardants

• Successful control of plant height using GR depends on crop, stage of crop, concentration, method of application, volume of application, coverage, and environmental conditions
• Foliar spray and soil drenching are two methods of application
• Uniform coverage is essential, and stem contact is crucial for effective application

Learn about plant growth retardants, synthetic organic compounds that inhibit cell division and elongation, and their effects on plant growth and development.