Involvement of silicon in pearl millet resistance to downy mildew disease and its interplay with cell wall proline/hydroxyproline-rich glycoproteins

Abstract

Conclusive evidence is presented here for the implication of silicon in the enhanced resistance of pearl millet to Sclerospora graminicola. Exogenous application of silicon dioxide through seed priming enhanced the germination and vigour of seed quality parameters. Further, with optimised conditions, seed priming in combination with SiO₂ soil drenching and foliar spray was effective at protecting pearl millet plants against downy mildew and reduced disease by 78% compared with the control. There is a positive relationship between silicon level in tissues of pearl millet of various cultivars and their degree of downy mildew resistance; for example, resistant cultivar IP19892 had 82 mg/g DW of silicon and highly susceptible cultivar 7042S had 31 mg/g DW of silicon. Exogenous application of silicon was found to augment the silicon level and resistance of the susceptible cultivar. Histological observation of leaves showed higher silicon accumulation in the resistant cultivar compared with the susceptible cultivar. During resistance development in plants treated with silicon, the structural fortification with hydroxyproline-rich glycoprotein was observed and this was relatively and directly proportional to the level of silicon deposition.