The influence of silicon on the components of resistance to gray leaf spot in St. Augustinegrass

Soil fertilization with silicon (Si) has been shown to reduce the severity of gray leaf spot, caused by Magnaporthe grisea, in St. Augustinegrass. However, to understand how Si reduces gray leaf spot, it is necessary to study the effects of Si on the components of host resistance. In a greenhouse, six rates (0, 0.5, 1, 2, 5, and 10 t ha(-1)) of calcium silicate were evaluated for their ability to affect the components of resistance to gray leaf spot in the susceptible ('Floratam') and resistant ('FX-10') St. Augustinegrass cultivars. Components of resistance assessed were incubation period, latent period, lesion number, lesion area, daily rate of lesion expansion, and number of conidia per lesion. Percent leaf area diseased, a result of the components of resistance, was also evaluated. In this study, the only component of resistance affected by Si was lesion number. Silicon application significantly reduced the number of lesions 26 to 61 % when compared to the untreated control in the susceptible cultivar 'Floratam'. In the resistant cultivar 'FX- 10', as the rate of calcium silicate increased the number of lesions decreased significantly from 43 to 57%. The percent leaf area diseased in 'Floratam' was significantly reduced (18-57%) by increasing rates of silicon when compared to the control. Silicon was the only element to increase significantly in the plant tissue from the amendment of soil with calcium silicate. Integrated disease management strategies for reducing gray leaf spot in both sod production and home lawn settings can be augmented by using Si fertilization to increase plant resistance to gray leaf spot, especially in soils deemed to be low in plant available Si.