The Potential of Silicon Soil Amendment to Reduce Severity of Fusarium Wilt of Cotton

Justification and objective
Silicon is a plant nutrient anomaly, considered beneficial, yet not essential for plant growth. There is evidence for relationships between the level of silicon available to the plant, accumulation of silicon in plant tissues, enhanced biochemical defences and resistance to disease.
The aim of this work is to examine the potential of silicon soil amendment to reduce severity of Fusarium wilt.
METHODS
Glasshouse trials
Naturally infested field soil was mixed 50:50 with sand. Two cotton cultivars were sown directly into the soil mix in seedling flats. Liquid treatments were applied weekly as a soil/seedling drench and powder formulations were mixed uniformly through the soil. At harvest, plants were examined internally and rated for disease severity.
Field trials
Three field trials were conducted at “Cowan” near Cecil Plains in Queensland, Australia to investigate the effect of various silicon sources applied to soil and leaves on silicon uptake, disease severity, seed cotton yield and fibre quality.
RESULTS
Glasshouse
Results suggest that silicon (and potassium) may play a role in suppression of Fusarium wilt of cotton, but only when more resistant cultivars are grown.
Field
Trial 1
Silicon uptake was significantly increased following silicon soil amendment in an alkaline soil; however there was no effect of silicon on disease severity. 
Trial 2 and 3
In these trials silicon uptake into the plant was not increased by Si amendment of the soil pre-plant, and there was no effect of Si on establishment, disease severity or seed cotton yield.
CONCLUSIONS
Significant reductions in disease severity were obtained following the application of silicon in glasshouse trials but these were not effective under field conditions.  In the field, inoculum levels may be too high for silicon to be effective. Also, placement of fertiliser may not have been conducive to silicon uptake.