The Mechanisms Underlying the Anthracnose Disease Reduction by Rice Hull as a Silicon Source in Capsicum (Capsicum Annuum L.) Grown in Simplified Hydroponics

Silicon has proven to be effective in controlling many diseases in plants and could be used as an alternative strategy against chemical control of diseases. Rice hull is an environmental friendly natural source of silicon. This study was conducted to investigate the effect of rice hull as a Si source on anthracnose disease and also on fruit cuticle thickness (CT), total soluble and cell wall-bound phenolic compounds (TSP and CWBP) in fruits and formation of fungal appressoria on fruits as possible mechanisms of disease reduction in capsicum (Capsicum annuum L.). In this study a simplified hydroponics system (SHS) with rice hull as an inert media and nutrients supplied with either NF (New Formula) or Albert's solution was used. A liquid hydroponic system (LHS) was also maintained with same nutrient solutions as controls. Disease development was assessed by challenge inoculation with Colletotrichum gloeosporioides on fruits. CT was measured using stage and ocular micrometer. TSP and CWBP in fruits were analysed by Folin-Ciocalteu method during first 5 days after inoculation (DAI). Appressoria formation by fungal conidia on fruit peels at inoculated spots was observed through micrometer daily after inoculation. More than 83% disease reduction was observed in fruits harvested from SHS compared to that of LHS supplied with both nutrient solutions. There were significantly higher values of CT and CWBP (about 45% and 30% respectively) in fruits from SHS compared to that of LHS (Si-free). However, TSP was not significantly affected by Si treatment. A higher percentage of appressoria was prevailed on fruits harvested from SHS thus the disease initiation was delayed compared to that of LHS. There may be a possibility that germination of appressoria was hindered by thicker cuticle or biochemical reaction involved with induced CWBP in fruits from Si treated plants.