Effect of silicon fertilisers on sugarcane SMUT in Australia

SMUT CAUSED BY the fungus, Sporisorium scitamineum, is an important disease of sugarcane in Australia. A trial was conducted in Bundaberg on a silicon-deficient sandy soil to determine the efficacy of soil-applied silicon for control of smut in two susceptible (Q157 and Q205), one intermediate (Q208) and two resistant (Q151 and Q200) varieties. Silicon was applied as air-cooled blast furnace slag (14-18% silicon) at 6 t/ha (8.1 kg/9 m row) to selected plots and incorporated using a rotary hoe. Test varieties were planted between spreader rows of smut-infected Q205. The trial was maintained for three years until second ratoon. Disease assessments were carried out prior to harvesting, and yield data were collected only in the second ratoon. The silicon levels in leaf tissue were significantly higher in silicon-treated plots compared to untreated controls. The highly resistant variety Q151 showed no smut in either silicon or untreated plots throughout the experiment. The intermediate to resistant variety Q208 had 3% smut in the silicon treatment and 6% smut in the untreated plots in the second ratoon crop and the moderately resistant variety Q200 had 12% smut in the silicon treatment and 8% smut in the untreated. These differences were not significant. At the final inspection in the second ratoon crop there were no significant differences in smut incidence between the silicon-treated and untreated plots of the susceptible variety Q157 (99 and 100% respectively), but significance differences were observed in Q205 (86 and 93% respectively). Tonnes of cane per hectare (TCH) and tonnes of sugar per hectare (TSH) were significantly higher in the silicon-treated Q208 compared with the untreated Q208. The highest TCH and TSH in this trial were obtained from Q208 with silicon (150 and 26 t/ha respectively). Silicon did not significantly increase TCH or TSH in the other varieties and no differences in commercial cane sugar (CCS) were observed between silicon treated and untreated varieties. This experiment showed that resistant and intermediate varieties are effective in controlling smut with no addition of silicon under very high inoculum pressure from the disease. Silicon did not control smut in highly susceptible varieties, but possibly minimised the adverse stress response in Q208.