Silicon mediates the changes in physiological performance, nutrient uptake, root colonization morphology and secondary metabolite activity in rubber rootstock seedlings (Hevea brasiliensis) inoculated with Rigidoporus microporus

White root disease (WRD) of rubber, caused by Rigidoporus microporus, is a severe soilborne disease in rubber plantations. Although several studies have addressed the potential use of silicon (Si) to combat plant diseases, the exact mechanisms underlying Si-improved physiological performance and resistance to WRD in rubber rootstock seedlings are still unknown. This study evaluated the effect of soluble Si supplementation in controlling R. microporus on 13-month-old rubber rootstock seedlings of clones RRIM 2002 and RRIM 2024. The application of soluble Si twice a month on the RRIM 2002 clone increased the relative chlorophyll content, photosynthesis rate, stomatal conductance and transpiration rate to 55.0%, 179.0%, 277.8% and 173.0% higher, respectively, than untreated seedlings 9 months postinoculation with R. microporus. Soluble Si supplementation reduced the disease by 55.0%, compared to only 25.6% disease reduction on rubber rootstock seedlings treated with propiconazole. The application of soluble Si enhanced the accumulation of Si and the production of total phenolic compounds (TPCs) in the rubber rootstock seedling roots by 40% and 25%, respectively, compared to untreated seedlings 9 months postinoculation with R. microporus. Based on scanning electron microscopy observations, the root tissue of rubber rootstock seedlings treated with soluble Si showed the absence of R. microporus hyphae, and the accumulation of Si granules was observed. Thus, this work proved that soluble Si in the form of silicic acid shows promising results as an alternative fertilizer in controlling WRD.

Automated summary

The supplementation of soluble silicon has been proven to be effective in controlling white root disease in rubber rootstock seedlings by improving their physiological performance and reducing the severity of the disease. It enhances chlorophyll content, photosynthesis rate, stomatal conductance, and transpiration rate, while reducing disease severity and increasing the accumulation of silicon and total phenolic compounds in the roots of the seedlings.