1. W. Roland Leatherwood 1 Neil S. Mattson 1 Possible Roles of Silicon and Regulated Deficit Irrigation on Poinsettia Plant Quality and Postharvest Performance 1 Department of Horticulture, Cornell University

2. Silicon Background Abiotic stress –Improved adventitious rooting (Moon 2008, Gillman 2000), Decreased leaf abscission (Gillman 2000) –Heat stress (Agarie 2008) –Drought Stress (Gao 2004, Agarie 2008) Horticultural characteristics –Flower diameter, stem caliper (Kamenidou 2008, 2005), branching (Moon 2008) Little on Si & Greenhouse Crops –Industry acceptance of Si as supplemental nutrient is uneven

3. Methods Plant material –‘Prestige Red’ and ‘Peterstar Red’ Poinsettia rooted cuttings –6” Pots, commercial media. –Nutrition N200 mg·L -1 (21-5-20) Mg 30 mg·L -1 (MgSO 4 · 7H 2 0) S32 mg·L -1 (MgSO 4 · 7H 2 0) Mo0.1 mg·L -1 (Na 2 Mo 4 · 2H 2 O)

4. Methods Treatment design –CRD, 15 replicates –Two way factorial of deficit irrigation and silicon supplementation 100, 80 and 60% RDI Si 0 and 56 mg·L -1 (KSiO 3 ) (2 mM) –Statistical analysis SAS V9.1 Tukey’s HSD with an α=0.05 –Irrigation water (RO) Si was ND and substrate Si concentration was 2.0 mg·L -1

6. Peterstar

7. CultivarTreatmentHeight (cm) Peterstar Si- 100%31.0 A Si+ 100%30.0 AB Si+ 80%29.7 BC Si+ 60%29.6 BC Si- 80% 28.8 BC Si- 60% 28.5 C Significance * n=15, NS = not significant, * = 0.05, ** = 0.01.

9. Peterstar

10. Prestige

11. Disease

12. TreatmentTotal Plants Effected Peterstar 1 Prestige 2 Si+ 100%00 Si+ 80%00 Si+ 60%00 Si- 100%11 Si- 80%11 Si- 60%01 Significance 1 χ 2 (2, n=15)=?, p=? 2 χ 2 (2, n=15)=?, p=?

13. Strength Photo B. Whipker

14. Strength CultivarTreatment Number of Plants with Breaks Average Break Height (cm) PrestigeSi+ 100%050 Si- 100% 2* 40* Si+ 80%140 Si- 80%150 Si+ 60%140 Si- 60%050 χ 2 (2, n=5)=3.95, p<0.0382

15. Findings Si interacts with plant water status giving differential results –No or moderate water stress, Si decreased height and bract area –Severe water stress, Si increased height and bract area Si improves lateral branch strength and may reduce Pythium occurrence.

16. Postharvest

17. Materials & Methods Plants were thoroughly watered Moved to postharvest December 1 st Leaf angle measured 12/1 and periodically thereafter terminating December 17 th Measured uppermost fully expanded free hanging green leaves (3x) 12 Hour day, florescent lighting, 21° C

18. Postharvest Wilt

19. Postharvest Wilt 17 Days Postharvest CultivarTreatmentLeaf Angle(°) Peterstar Si- 100%42.1 A Si- 60%34.0 AB Si- 80%28.4 B Si+ 100%25.5 B Si+ 60% 21.8 B Si+ 80% 21.0 B Significance ** n=10, NS = not significant, * = 0.05, ** = 0.01.

20. Postharvest Wilt

21. Bract Edge Burn

22. TreatmentTotal Lesions Peterstar 1 Prestige 2 Si+ 100% 10 1 Si- 100% 21* 6* Si+ 80%201 Si- 80%221 Si+ 60%12 0 Si- 60%6* 2* Significance 1 χ 2 (2, n=10)=5.49, p<0.0201 2 χ 2 (2, n=10)=1.91, p<0.0835

23. Findings Si supplementation forestalls wilt and may improve recovery from water stress There may be interactions with RDI and Si Si supplementation reduces BEB in well watered plants and may increase it in water stressed plants

24. Acknowledgements Post/Schenkel Endowment USDA Hatch Funds Ecke Ranch Rachel Brinkman