10 - Plant Growth Retardant (Lect 10).pdf

Pengawalatur Tumbesaran HRTPlant 4300 Growth Regulators LECTURE 10  PLANT GROWTH RETARDANT (GR) synthetic organic compounds that cause retardation / inhibition of cell division and / or elongation produce no significant growth defects / malformations...

Pengawalatur Tumbesaran HRTPlant 4300 Growth Regulators LECTURE 10  PLANT GROWTH RETARDANT (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 prodn. of leaves or on root growth reduce stem elongation, increase green color of leaves  PLANT GROWTH RETARDANT (GR) block specific sites in pathways of PGR biosynthesis (esp. Gibberellins biosynthesis) result in many biochemical & physiological changes ~ e.g. inhibition of key steps in GA biosynthesis regulation of sterol synthesis in plants Gibberellins biosynthetic Pathway Gibberellins  STEROLS an essential component of cell membrane plants & animals produce sterols ~ cholesterol is exclusively an animal sterol ~ plant sterols (phytosterols) : 40 plant sterols identified sitosterols, campestrols & stigmasterols most abundant plant sterols lower serum conc. of cholesterol PLANT GROWTH RETARDANT (GR) important in agric. & hort. in control of vegetative growth ~ shortening internodes, reduce plant height Examples of GR ancymidol chlomequat daminozide flurprimidol mefluidide paclobutrazol tetcyclacis unicozole Use of Plant Growth Retardants 1. Reduce plant height ~ important in floricultural crops done without adversely affecting aesthetic quality ~ GR used to manipulate size, shape, overall quality ~ Poinsettias, Chrysanthemum, Easter Lily : CCC, daminozide, ancymidol, paclobutrazol, unicanozol, tetcyclacis Poinsettia : Chlormequat chloride, CCC - most effective in reducing height - less expensive than Ancymidol Chrysanthemum : Daminozoid : foliar spray Ancymidol : foliar spray, soil drench − appln. of GR → shorter, more rigid, darker greens Easter Lily : Ancymidol : most effective in reducing height other compounds : Paclobutrazol Triademefon  Bedding plants : Zinnia, geranium Daminozide Paclobutrazol control height of bedding plants Zinnia elegans zinnia flowers (500 x 375) Use of Plant Growth Retardants 2. Reducing growth of turf grass control of grass growth esp. on sites (highways, dividers, airfield) – difficult / dangerous to maintain − e.g. several compounds : Chlorflurenol Paclobutrazol Melfluidide inhibiting cell division in the shoot meristem Use of Plant Growth Retardants 3. Advancing fruit color dev. GR like Daminozide advances anthocyanin production in fruit skin and flesh in sweet cherry Use of Plant Growth Retardants Daminozide increases anthocyanin synthesis, decreases fruit drop reduces fruit softening during cold storage in apples Use of Plant Growth Retardants 4. Induction of flower bud formation Daminozide stimulates flowering in apples and pears − stimulation through inhibition of vegetative growth 5. Controlling tree size Paclobutrazol effective for controlling shoot elongation in fruit trees − maintain tree height for spraying & harvesting efficiency Use of Plant Growth Retardants 6. Lodging control in cereal Chlormequat chloride : reduces stem height & diameter  yield increase Wheat, barley, rye 7. Increasing fruit set Chlormequat chloride : increases fruit set in grapes Use of Plant Growth Retardants 8. Other Miscellaneous GR Compounds Maleic hydrazide : prevents bud sprouting in onion & potatoes Citrus abscision agents Release and Pick-off induce abscision in citrus – for mechanical harvesting Application of Plant Growth Retardants Successful control of plant height using GR depends on : Crop ~ dif. crops respond differently ~ type of GR, optimal conc. dif. Stage of crop ~ more or less sensitive to GR at dif. growth stages Concentration ~ optimal conc. bet. crop & type of GR Application of Plant Growth Retardants Method of application ~ foliar spray, soil drenching ~ soil drenching – more exact amount of chemical to be applied Volume of application ~ foliar spray /soil drenching differ in volume Coverage & Uniformity ~ uniform coverage is essential ~ stem contact essential Application of Plant Growth Retardants Environmental conditions ~ less effective at high temp. ~ potential for phytotoxicity at high temp. ~ low light, high humidity, cool temp. more effective – drying rate slower GR – slow absorption THE END