Growth Stimulants, Retardants, and Rooting Hormones

1. Growth Stimulants, Retardants, and Rooting Hormones

2. Growth regulators • Hormones • Organic chemicals that act and interact to affect growth rate • Auxins – accelerate growth by stimulating cell enlargement

3. Gibberellins • Stimulate growth in stem and leaf by cell elongation • Stimulates premature flowering, growth of young fruits and breaking of dormancy

4. Cytokinins • Stimulate cell division • Work along with auxins • Will not work without auxins present

5. Inhibitors • Abscisic Acid and Ethylene Gas • inhibits seed germination • Inhibits stem elongation • Hasten ripening of fruit – ethylene gas

6. Auxins and Gibberellins promote cell enlargement • Cytokinins stimulate cell division

7. Growth Hormones • Organic chemicals produced by actively growing plant tissue • Shoot tips and young leaves • Move throughout the plant and can be found in most tissues

8. These chemicals react with one another in a very complex system in the plant • In some cases a concentration of one hormone stimulates growth and a different concentration restricts growth

9. Apical Dominance • Dominance of the terminal bud • Apical dominance exists there • Terminal bud secretes chemicals that inhibit or prevent the growth of axillary buds on the same shoot

10. Apical Dominance • Axillary buds are found in the axil – angle between a leaf and the stem. • Causes the plant to grow tall and not branch • Once the plant reaches flowering age and the terminal bud becomes a flower, the chemicals are no longer secreted

11. Apical Dominance • The plant then starts to send out side branches • This allows the plant to grow above competing plants • Once height and access to sunlight are secured, the plant spreads out over its competitors

12. Apical Dominance • Pinching off terminal buds removes the hormone and causes branching to happen faster • Common practice in greenhouses and nurseries to produce bushier plants with many flower buds

13. Stimulants • Allow plants to grow taller • Most common is Gibberellic Acid (GA) • Causes stems of plants to stretch out • Nodes are farther apart

14. Growth Stimulants • Natural growth stimulants have been found in alfalfa • It causes stimulation of growth • It is the alcohol called Triacontanol • Stimulation is brought about by mulching plants with alfalfa hay

15. Or watering plants with a “tea” made from soaking alfalfa feed pellets in water • Amount needed is very small • Also sold commercially

16. Chemical Retardants • Chemicals are used to retard growth of plants causing them to be shorter and more compact • Plants are more attractive and the plants themselves are stronger • Used commercially • B-Nine is commonly used on Azaleas

17. Newest uses of Plant Growth Retardants (PGR) is the application to lawns • After first mowing in the spring “Limit” is applied and absorbed by the roots • Restricts growth for 6-8 weeks

18. “Embark” is absorbed by the leaves and also restricts growth • PGR’s absorbed by the leaves move to the growing point where it interrupts cell division, stem elongation and seed head formation • Roots continue to grow • Applied after first or second mowing

19. Sumagic • New growth retardant • Reduces height of plants by inhibiting production of GA • Chemical is taken up by leaves and moves through the plant to the terminal bud

20. Used to control growth of shrubbery and hedges • PGR Atrimmic applied after pruning can last an entire season • Reduces or eliminates the need to prune

21. Atrimmic • A systemic • Penetrates the plant, enters the plant sap, and moves through the plant • Blocks plant hormones that stimulate growth • Applied as a foliar spray

22. Rooting Hormones • Important when propagating plants by cutting • Helps cuttings to develop more roots faster than without a rooting hormone • Indoleacetic Acid (IAA) naturally occurring, causes roots to form on plant stems

23. IBA – Indolebutyric Acid • Most widely used rooting hormone • Most effective rooting hormone

24. Rooting Hormones • Either mixed with talc and used as a powder or dissolved in water and used as a wet dip • Liquid can be slightly more effective • All rooting hormones should contain a fungicide

25. Fungicide • Helps prevent cuttings from rotting

26. Dwarfing Rootstock • Used in fruit trees • Shorter trees enable you to pick fruit without using a ladder • First research done to prevent apple trees from growing very tall • Trees growing from certain types of roots didn’t grow as tall

27. These trees also bore fruit at an earlier age • Complete series of rootstock known as malling rootstock developed in England • Controls size and rate of growth or apple trees

28. Stock has also been developed for peach and pear trees as well • Dwarf trees can be purchased commercially

29. Chemical Blossom Set • Used on tomato blossoms early in the season • Causes earlier development of fruit • Causes seedless tomatoes to set on first blossoms and results in tomatoes ready to eat as much as 10 days earlier than normal

30. Plant Biostimulants • Natural products • Organic • Work to stimulate soil microbial activity and improve soil cation exchange capacity, stimulate plant growth and promote disease resistance

31. Humic Acid • Product of rotting organic matte is an example of a soil microbial stimulant

32. Root growth biostimulants • Improve water and nutrient uptake • Increase number of fibrous roots • High levels found in kelp plants

33. Biostimulants • Greatly reduce the need for fertilizers, especially N • Saves money, reduces pollution

34. Methanol • A form of alcohol • Speeds plant growth • Research in California showed an increase in plant yield of 36-100% • Works by blocking photrespiration • Plants use water for growth rather than transpiring it into the air

35. Methanol • Works best on plants frown in full summer sun • Water use reduced by as much as 50% in some plants

36. Allelopathy • Production of a chemical compound in one plant that slows or stops the growth of another plant • Natural herbicide • Black Walnut, Millet