Silicon Supplementation and Regulated Deficit Irrigation Improve Poinsettia Quality and Postharvest Performance

The effect of silicon on improving quality of container plants grown in soil-less substrates is an area of active study.  Improved stress tolerance, mechanical strength and disease resistance have been reported for several species, as well as changes in plant architecture and inflorescence size.

To investigate possible beneficial effects of substrate applied Si in Poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) production; plants of ‘Peterstar Red’ and ‘Prestige Red’ poinsettias were grown under appropriate greenhouse conditions.  The treatment design was a factorial arrangement of two Si concentrations, 0 and 56 mg · L^-1, and three irrigation regimes, 100, 80 and 60% regulated deficit irrigation (RDI).  Regulated deficit volumes were established gravimetrically using several well watered (100%) reference plants.  Plants were evaluated for a variety of factors during production and postharvest storage.

We observed significant main effects of Si and RDI in postharvest water stress tolerance, as measured by degree of wilt.  Leaf wilt angle was reduced 40% in Si amended plants and 30% in RDI (60 and 80%) plants after 15 days of simulated postharvest storage without water.  Si amended plants exhibited improved recovery from severe wilting.  RDI (60 and 80%) reduced overall height of plants by 5 to 10% and bract area 34 to 36%.  However, Si supplementation offset some reduction in bract size in the 60% RDI plants, yet decreased bract size in the 80 and 100% RDI plants.

Mechanical strength was increased by Si supplementation resulting in significantly reduced breakage and increased branch strength.  By using a drop test of increasing 10 cm heights, we found that, across all RDI treatments Si supplementation reduced breakage 33 to 50%.  The height at which the first broken branch occurred was 20% greater in Si amended plants compared to unamended plants.

Bract edge burn (BEB), which is associated with disrupted water relations and Ca nutrition, was reduced 53 to 84% by Si amendment in 100% RDI plants, yet Si had no effect on BEB in 80% RDI plants and increased BEB in 60% RDI ‘Peterstar Red’ plants. 

These results support the use of RDI and Si in poinsettia production programs as methods of improving overall crop quality and in particular postharvest quality.