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XV. PHOTOPERIOD

XV. PHOTOPERIOD. A. Natural Photoperiod Yearly variation 9.5 to 14.5 hrs in KY 0 to 24 hrs at North pole Cause Tilt of earth axis. B. Description - plants Definition Effect of the length of night on many morphogenetic changes in the plant ; elongation of internodes

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XV. PHOTOPERIOD

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  1. XV. PHOTOPERIOD A. Natural Photoperiod • Yearly variation • 9.5 to 14.5 hrs in KY • 0 to 24 hrs at North pole • Cause • Tilt of earth axis

  2. B. Description - plants • Definition • Effect of the length of night on many morphogenetic changes in the plant; • elongation of internodes • enlargement of leaves • flowering

  3. Plant in light Red Pr 660 Pfr 730 Far red Plant in darkness • Characteristics • Low light intensity reaction • red/farred light • short duration (1-4 hrs) at night

  4. C. Critical Night Length - CNL 1. Definition for long night plant - LNP • The minimum number of continuous hours of darkness at a given temperature that will permit the most rapid flower bud initiation (a period longer than the CNL will cause delay in initiation). 2. CNL is temperature dependent • Number of hrs of continuous darkness decreases as temperature increases 3. CNL for short night plant • Maximum number of hours of darkness that permits bud initiation

  5. D. Night length Control 1. Lengthening the night • Reduce light intensity to less than 2-3 ft.cds. • Black cloth or plastic • manual • automatic

  6. Time of covering • Goal: • maximum photosynthesis/ photoperiod response • Normal 5 pm to 7 am • Ideal as much high light as possible but satisfy CNL • Problems • Heat build-up

  7. 2. Shortening the night a. Incandescent light • Intensity • greater than 10 ft.cds. • 60 w; 4ft space; 2 ft above plants • 100 w; 6ft space; 3 ft above plants • Time • middle of night • June & July 1 hr • Aug & May 2 hrs • Sept-Oct & Mar-Apr 3 hrs • Nov-Dec & Jan-Feb 4 hrs

  8. 2. Shortening the night • b. Cyclic Lighting • 20% of time • 10:00 - 10:06pm • 10:30 - 10:36 • 11:00 - 11:06 • 11:30 - 11:36

  9. Plant in light Red Pr 660 Pfr 730 Far red Plant in darkness

  10. Red Farred Dark

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