Effect of Integration between Vascular Arbuscular Mycorrhizal Fungi and Potassium Silicate Supplementation on Controlling Onion White Rot

The inhibitory effect of potassium, calcium and sodium silicate was assessed, in in vitro at different concentrations (0.1, 0.5 , 1, 2, 4 and 8ml /l) against Sclerotium cepivorum the causal of onion white rot . The results indicated that potassium and calcium silicate at 0.5 ,1,2,4 and 8ml/l inhibited the mycelial growth and sclerotia formation of S. cepivorum, but at 0.1ml/l concentration, the mycelial growth decreased to (2.4cm and 5.0 cm) respectively compared with control treatment . On the contrary sodium silicate resulted in low effect on the mycelial growth and sclerotial formation. Our results also showed that, potassium and calcium silicate increased the pH of the PDA medium from 8.8 to 11.4 by increasing K2SiO3 and from 8.7 -11.5 by increasing CaSio3 concentration from 0.1to 8 ml/l. Under greenhouse conditions, the incidence of white rot disease was significantly decreased when onion plants were treated with potassium silicate(2,4 and 8ml/l) only or with VAM fungi, as soil drench in potted soil infested with S. cepivorum compared with the control. Adding 4ml/l potassium silicate as soil drench showed high reduction to the disease incidence by 71.43%. On the other hand, onion plants treated with different concentrations of potassium silicate as soil drench and VAM fungi or Folicur 25%, increased apparently healthy survived plants at harvest under field conditions of Kalubiya Governorate during 2015/2016 and 2016/ 2017 seasons, since they decreased disease infection percentages. The highest reductions of onion white rot were observed when onion plants were treated with Folicur 25% followed by potassium silicate at (2 ml/l +VAM fungi). Regarding the yield of onion bulbs, our results indicated that all treatments showed significant increase to bulb yield in contrast to the non-treated plants. Spores count and percentage of root colonization with VAM fungi were increased by increasing potassium silicate concentration, in contrast to the percentage of hypha which was increased by decreasing potassium silicate concentration. In addition, VAM fungi and VAM+ 2ml/l potassium silicate treatments were considered the best treatments to give the best hyphal percentage 93% and 80% respectively.