Abstract
Rice husk is a natural Silicon (Si) source. This study evaluated the effect of rice husk in two different forms; ground rice husk (GRH) and rice husk ash (RHA) on downy mildew in bitter gourd (Momordica charantia L.) leaves caused by Pseudoperonospora sp. Rice husk was added to the growing medium to achieve the final concentration of 200 mg Si /kg soil. Si accumulation in leaves, disease severity, plant growth parameters, cuticle-epidermal layer thickness, chlorophyll content, total phenolic content, peroxidase (POD) and polyphenol oxidase (PPO) activity of leaves were measured. Husk treatment lowered the downy mildew severity significantly (p < 0.05) in leaves although the difference between the effects of two husk forms was insignificant. Numbers of leaves, flowers and fruits in husk-treated plants were significantly higher (p < 0.05) than those in control plants. Cuticle-epidermal layer thickness in GRH, RHA-treated and control plants were 16.8 ± 1.21, 18.2 ± 0.98 and 13.2 ± 1.27 μm respectively. Total phenol content, POD, PPO activity and chlorophyll content in rice husk-treated plants were significantly (p < 0.05) higher than that of control plants. The enhanced disease resistance in rice husk-treated plants appears to be positively associated with the higher accumulation of silicon and Si-enhanced phenolic content and increased activity of PPO and POD enzymes in leaves.
Highlights
Rice husk (RH) is the sheath which forms the cover of rice grains during their growth
We previously reported that the root application of soluble Si reduces the severity of major foliar fungal diseases in bitter gourd (Momordica charantia L.) including powdery mildew caused by Erysiphe sp. and downy mildew caused by Pseudoperonospora sp. (Ratnayake et al, 2014, 2015, 2016a and 2016b)
Rice husk was used in two different forms viz. ground rice husk (GRH), which was obtained by grinding the rice husk on laboratory scale grinder and rice husk ash (RHA),which was obtained by burning in a Muffle furnace at 500oC for 5 hours
Summary
Rice husk (RH) is the sheath which forms the cover of rice grains during their growth It is one of the most widely available agricultural by-products in rice producing countries throughout the world, which accounts for 20% of the annual world rice production (Battegazzore et al, 2014). Rice husk is used for different purposes; as a fuel, as material for animal husbandry, as biofertilizer, as a raw material for construction industry etc. It is still an under-utilized product of rice milling and often burned in open air or dumped on wasteland. Numerous reports suggest that black to gray RHA can be effectively used in rice nurseries and in the main rice fields to achieve healthy seedlings and higher yields. As reported by Jayawardane et al (2014), leachates from RH (which was produced by soaking RH in water) was effective in enhancing growth, yield and resistance against anthracnose disease in capsicum
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