Control of Plant Height and Branching in Ornamentals Ep Heuvelink Horticulture and Product Physiology group, Wageningen University, the Netherlands
Compact plants = desired external quality Currently often realised by using growth retardants, but: Societal pressure (environment) Costs (chemicals, labour) Not always sure, sometimes even crop damage Search for alternatives: What is known? How do these alternatives work?
Factors influencing elongation 1. Genetic factors: cultivar choice Eight different Kalanchoe cultivars, grown without growth retardants; same conditions, large difference in elongation
Factors influencing elongation: 1. Genetic factors: cultivar choice 2. Aerial environment Climate (temperature, light, CO 2, humidity), planting density
Lower temperature: shorter plants but longer cultivation time (Kalanchoe blossfeldiana) Licht intensity: 200 μmol.m -².s -1 o C: 18 21 23 26
Cultivar differences in temperature response 16 C 20 C Biaritz Chrysant 16 C 20 C Dublin
Influence of temperature pattern DIF: Difference between day and night temperature DROP: Short period of low temperature DIF DROP
DIF experiment (chrysant) in climate rooms (12h day, 12 h night) 4 day temperatures 16 o C 20 o C 24 o C 28 o C 4 night temperatures 16 o C 0 DIF +4 DIF +8 DIF +12DIF 20 o C -4 DIF 0 DIF +4 DIF +8 DIF 24 o C -8 DIF -4 DIF 0 DIF +4 DIF 28 o C -12DIF -8 DIF -4 DIF 0 DIF
DIF effect on internodium length chrysanthemum Internodium length (mm) 30 25 20 15 10 5 0-16 -12-8 -4 0 4 8 12 16 DIF ( C) DT: 16 ºC; 20 ºC; 24 ºC; 28ºC
Effect of temperature DROP from 20 to 12 o C on internode length in tomato (climate room) Elongation is most sensitive to temperature at the beginning of the light period Source: Langton, 1998 Source: Langton, 1998
Influence of light spectrum (petunia) 20 days after start light treatment, 50 days after sowing LEDs HPS Solar light 70% Red 30% Blue 16 h light, 100 µmol PAR.m -2.s -1 20 o C no DIF no DROP Optimum water and nutrient supply
Influence of light spectrum (petunia) 20 days after start light treatment, 50 days after sowing More red light (with background solar light) results in more compact plants 100 Solar light 0 Red LEDs 80 Solar light 20 Red LEDs 50 Solar light 50 Red LEDs 16 h light, 100 µmol PAR.m -2.s -1 20 o C no DIF no DROP Optimum water and nutrient supply
Phytochrome Photoreceptor, exists in two forms that are interchangeable farred P r P fr (= active form, limits elongation) red After sunset (dusk) red-farred ratio is low, this stimulates elongation!
Cut off natural day (no dusk) plant stays shorter 8 hours 8 hours daylength Natural daylength + 1 h farred daylength Source: Dr. Theo Blom, University of Guelph, Ontaria, Canada
Filter out farred light (seedling production) (photoselective plastic film) 5 Source: Runkle en Heins, 2002 Plant length (cm) Plant lengte (cm) 4 3 2 1 Impatiens Petunia 0 Control Controle Filter Problem: less total light (PAR), delay in flowering possible
Planting density Leaves absorb most of the red light and farred light is transmitted or reflected Hence low red/farred ratio in a dense canopy, resulting in more elongation
Factors influencing elongation: 1. Genetic factors: cultivar choice 2. Aerial environment Climate (temperature, light, CO 2, humidity), planting density 3. Root environment Nutrient availability (e.g. low phosphate) EC, water content Potting soil (e.g. adding clay particles) / pot size
Reduced phosphate availability Petunia Blue ; no PG-mix as basic nutrition P in gietwater: 0.5 0.2 0.1 0.01 (mmol per liter)
Factors influencing elongation: 1. Genetic factors: cultivar choice 2. Aerial environment Climate (temperature, light, CO 2, humidity), planting density 3. Root environment Nutrient availability (e.g. low phosphate) EC, water content Potting soil (e.g. adding clay particles) / pot size 4. Stress factors Mechanical stress (e.g. brushing, moving) Cold water stress 5. Growth regulators (plant hormones & growth retardants)
Mechanical stress reduces elongation Source http://taspo.de
Regulation of Axillary Budbreak in a Cut-Rose Crop Production system in cut rose: Upright shoots and bent leaf package Frequent re-bending and pruning necessary to maintain desired plant architecture Harvest of flower crop: continuous or flush
Bud break in cut-flower rose production Number of breaking buds affects yield: Number of flowering shoots Quality of flowering shoots (stem length and weight, flower size) Definition of bud break: The bud becomes longer than 1.5 cm
Research question Which factor determines the number of buds breaking after shoot harvest? 1. Increased light intensity 2. Increased red:far-red ratio 3. Changed source:sink ratio 4. Correlative inhibition exerted by other shoots on the plant
Experiment: Number of competing shoots 0, 1, 2, 3 or 4 shoots per plant Bud break on blue shoot remainder Cultivar Akito grown in glasshouse on Rockwool slabs 0 1 2 3 4
Fewer breaking buds at higher number of competing shoots 3.5 2 2 Number of breaking buds (per plant) 3.0 2.5 2.0 1.5 1.0 0.5 LS D 0.0 0 1 2 3 4 Number of shoots (per plant)
Estimating plant source-sink ratio One similar growing shoot on each plant, except 0 shoots treatment Growth (dry matter increase) was estimated Growth of top shoot as fraction of growth of top shoot in 1 Shoot treatment measure for source/sink ratio 0 1 2 3 4
Relation to source-sink ratio 2.5 Number of broken buds (per plant) 2.0 1.5 1.0 0.5 1 Shoot 2 Shoots 3 Shoots 4 Shoots 2 2 0.0 0.6 0.7 0.8 0.9 1.0 1.1 Source-sink ratio One dot is one plot (14 17 plants) Bars show SE of mean
Previous graph suggests: No. of growing shoots on the plant influences bud break via source:sink ratio Test by influencing the source:sink ratio in other ways e.g. Shading or Removal bend shoots
Source:sink ratio not explanatory: removal of leaves from bend canopy decreased source:sink ratio but increased 3.6 budbreak Bud outgrowth (# plant -1 ) 3.4 3.2 3 2.8 2.6 2.4 2.2 1S 2S Shade NoL Min 2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Source-sink ratio
Summary of 4 experiments Light Light Correlative Source: Name of Experiment intensity spectrum inhibition sink Number of young shoots + + + + Effect of bent shoot + - - -Position parent shoot + + Manipulate source:sink + +/- + +/- + = hypothesis supported - = hypothesis contradicted Is main factor light intensity or light spectrum?
Influencing light intensity and R:FR ratio
Higher light intensity at same red:far-red ratio stimulated bud break Bud break (no./shoot remainder) Daily PAR integral (mol m -2 d -1 ) Bud break (no./shoot remainder) Daily PAR integral (mol m -2 d -1 )
Bud break (no./shoot remainder) Different red:far-red ratio at same light intensity did not influence bud break Red:far-red ratio Bud break (no./shoot remainder) Red:far-red ratio
Conclusions From the 4 factors changed after shoot harvest: 1. Increased light intensity 2. Increased red:far-red ratio 3. Changed source:sink ratio 4. Correlative inhibition exerted by other shoots on the plant Increased light intensity (at bud level) is most important for bud break
Thank you for your attention! Co-workers Gerhard H. Buck-Sorlin Susana Carvalho Leo F.M. Marcelis Filip van Noort Jan Vos A. Maaike Wubs Most of the rose budbreak work has been recently published: Wubs et al. 2013. J. Am. Soc. Hort. Sci. 138: 243-252. Wubs et al. 2014. J. Am. Soc. Hort. Sci. 139: 131-138. Report on compact floricultural crops http://library.wur.nl/webquery/wurpubs/364793