No abstract

Effect of soluble silicon (Si) on downy mildew in bitter gourd (Momordica charantia L.) leaves caused by Pseudoperonospora cubensis was tested using three concentrations of liquid potassium silicate (100, 200, 300 mg Si/kg) added to the growing medium containing top soil, compost and sand. Disease severity, plant growth parameters, silicon accumulation on leaves and cuticle-epidermal layer thickness of transverse sections of leaves were measured. Si treated plants exhibited less disease severity than that of control plants and 200 mg Si/kg treatment resulted in highly significant disease suppression (37 -53% reduction against controls). The suppression of the disease strongly correlated with the Si accumulation in leaves. Cuticle-epidermis thickness was higher in Si-treated leaves (17.2 -21.3 µm) against non-treated (10.3 -13.81 µm). Numbers of leaves, flowers or fruits in Si treated plants were significantly higher (p < 0.05) than control plants except in 300 ppm Si level. Structural changes created by Si may at least be partly responsible for reducing the fungal disease severity in bitter gourd leaves.

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.

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The objective of the work reported herein was to optimize the growth conditions, and study the bioremediation efficiency and simultaneous biomass productivity of Chlorella vulgaris grown in water contaminated with Cd2+, Pb2+ ions and nutrients (NO3− and PO43−). In this regard, Chlorella sp. were cultivated separately in the presence and absence of known concentrations of Cd2+, Pb2+ and PO43− ions in growth media containing 200 mg L− 1 of NO3− for 30 days at ~ 28°C. The biomass, % oil content and the remaining Cd2+, Pb2+ and PO43− concentrations in the growth medium in 30 days after the cultivation were determined. The results revealed that the maximum tolerable Pb2+, Cd2+, total nitrogen (TN) and total prosperous (TP) concentrations were 8 mg L− 1, 2.5 mg L− 1, 200 mg L− 1 and 10 mg L− 1, respectively for living Chlorella sp. Biomass yields (% oil content) of Chlorella sp. grown in the absence of heavy-metal ions, in the presence of Pb2+ and Cd2+ ions in the growth medium were 0.8260 g L− 1 (40.69%), 0.5551 g L− 1 (37.64% ) and 0.2896 g L− 1 (44.80%), respectively, implying no significant reduction in % oil production caused by these metal ions. The extracted bio-oil was almost free from Pb2+ and Cd2+ ions. The bioremediation efficiency of Chlorella sp. was significantly high; 77% PO43− (from 10 mg L− 1), 84% Pb2+ (from 8 mg L− 1) at pH 5 and 72.7% Cd2+ (from 2.5 mg L− 1) at pH 6.