Efficiency of some Silicon Sources for Controlling Damping-off of Coriander (Coriandrum sativum L.) in Egypt

Isolation trials from infected coriander seedlings and plants growing in Qalubiya and Sharkiya governorates, showing symptoms of damping-off, root-rot, stem-rot and/or wilt diseases, yielded Alternaria alternata, Fusarium oxysporum, F. moniliforme, F. solani, Pythium sp., Macrophomina phaseolina, Rhizoctonia solani and Sclerotinia sclerotiorum. However, R. solani recorded the highest mean of frequency in isolation (19.1%), followed by S. sclerotiorum (13.5%) and F. oxysporum (13.2%), while A. alternata was the least (5.7%). The seven tested fungi were found to be pathogenic to coriander seedlings. F. oxysporum, R. solani, and S. sclerotiorum were the most virulent fungi, causing the highest damping-off incidence. Three silicon (Si) sources, i.e. calcium silicate, potassium silicate and sodium silicate with four concentrations (100, 200, 400 and 800 ppm), significantly inhibited mycelial growth of the seven pathogenic fungi to coriander seedlings. Potassium silicate at 400ppm was more effective than the other silicon sources tested, since it completely inhibited mycelial growth of the tested fungi. Under greenhouse conditions, damping-off (pre- and post-emergence) was completely controlled in the case of F. oxysporum by using Vitavax/Thiram whereas, post-emergence damping-off caused by any of F. moniliforme and F. solani was effectively controlled using either Vitavax/Thiram or potassium silicate. Also, applying the three silicon sources as soil drench to the infested soil significantly decreased percentages of damping-off, subsequently increased survival plants as well as improved plant height and fresh weight. Under field conditions, seeds soaking plus soil drenching by calcium silicate (800 ppm), potassium silicate (400 ppm) or sodium silicate (800 ppm) significantly reduced the incidence (%) of damping-off and increased plant height, number of branches and blossoms. Also, seed yield/plant and essential oil seed contents were improved. However, potassium silicate was the most effective treatment in reducing damping-off incidence and in improving plant growth parameters as well as seed yield and seed oil yield.