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Abstract:The resistance against anthracnose was investigated in tomato cutivars 'Thilina' and 'Maheshi' by soil application of silicon (Si) at 0 (control), 50 and 100 mg/L during the growth stage, flowering stage and both growth and flowering stages. It showed a reduction of lesions by 80 % in 'Maheshi' and 87 % in 'Thilina', respectively compared to the control irrespective of the cultivar and stage of the plant at which the treatment was given. Application of potassium (K) at twice (X2) and thrice (X3) the recommended dose to the plants reduced lesion size by over 30 % or 85 % in 'Thilina' and 'Maheshi' cultivars, respectively. In 'Maheshi, Si applied at 50 and 100 mg/L at all stages showed a significantly higher (p ≤ 0.05) fruit size compared to the control. Plants treated with higher doses (X2 and X3) of K also showed significantly higher fruit sizes compared to the control. Fruit firmness significantly increased in 'Maheshi' treated with 50 and 100 mg/L Si applied at the growth or flowering stage. A significantly lower percentage of total acidity (TA %) was observed in 'Thilina' treated with 50 or 100 mg/L Si irrespective of the stage of plant. 'Thilina' treated with X2 or X3 doses of K showed significantly higher (p ≤ 0.05) total soluble solid (TSS). Also, the percentage number of appressoria formed (number of spores with appressoria/total number of spores × 100) on areas inoculated with the fungus were significantly higher in fruits treated with X3 K dose and all Si treated fruits compared to the control.

Introduction Silicon is beneficial for many plants for growth, yield and enhancing resistance to biotic and abiotic stresses. In the present study, silicon as a form of rice hull sand mixture (3:2 v/v) was used in simplified hydroponic system to evaluate the performance and disease resistance of Capsicum annuum L. The nutrients were supplied by NF (New Formula) or Albert's solution. Results Continuous monitoring of soluble silicon content in the simplified hydroponic boxes revealed that a high amount of silicon was leached by the rice hull sand medium. Disease resistance was assessed by challenge inoculation of harvested fruits with anthracnose-causing fungi, Colletotrichum gloeosporioides, and it was observed a significant disease reduction (over 83 %) in fruits harvested from simplified hydroponic system compared to that of liquid hydroponic system. Shoot length, root length, fruit length, fruit weight and fruit firmness were also increased significantly in simplified system compared to the liquid system. However, the results were not significantly affected by the nutrient solutions used in these two systems. Conclusions In conclusion, the simplified hydroponic system composed of rice hull, as a natural silicon supplement could be used as a low-cost environmental friendly growing method of capsicum to enhance resistance against anthracnose disease, and to improve plant growth and fruit quality.

Silicon (Si) has proven to enhance disease resistance in a wide range of tropical fruits and vegetables. It has been used in controlling various diseases: mildews, rots, moulds, wilt, blight, anthracnose and leaf spots. However, the highest number of records was available on reducing diseases of powdery mildews on fruits and vegetables belonging to the family Cucurbitaceae. Siliconmediated defense responses in plant pathosystems are mainly attributed to the physical resistance, which involves reduced penetrability and/or increased hardness and abrasiveness of plant tissues because of silica deposition. The main mechanism is the chemical resistance, which involves chemical defenses to pathogen attack through the enhanced production of defensive enzymes and the production of antifungal compounds such as phenolic metabolism products, phytoalexins and pathogenesis related proteins. Silicon has been applied as soluble silicates to the substrate or to soilless media at pre-harvest level on reducing disease susceptibility. Post-harvest dips of fresh produce in silicate solutions and use of Si combined with a biocontrol agent are other aspects of silicon application in controlling diseases in fruits and vegetables.

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The development of powdery mildew i n t h e Ieaf of Pedilanthus tithymaloides var. caculatus by Oidium mangiferae and associated changes in the host were studied. The disease development occurred through a series of distinct changes in symptoms. Initial whitish, powdery patches of mildew infections became gradually colonized by a mycoparasite, Ampelomyces quisqualis (Syn. Cicinnobolus) pving the affected areas a greyish appearance. Further advancement of the disease rendered t h e tissue chlorotic which subsequently transformed into a bright pinkish-red colour. Towards the end of the-dryseason, certain infected areas became corky and suberized. Higher rainfall reduced both the intensity of powdery mildew and the growth of the mycoparasite. Typical powdery mildew symptoms were induced by artificial inoculation of young leaves with conidia of 0. mangiferae. A significant alteration of leaf pigment composition occurred when the infected areas turned to a pinkish-red colour. These areas lacked chlorophyll-a b u t contained other photosynthetic pigments plus several additional anthocyanins that were absent in healthy tissues. The healthy leaves of P. tithymaloides showed a clear pattern of diurnal fluctuation of acidity and stomata1 aperture on a scale similar to a known CAM plant, Kalanchoe sp. The major acid was found to be malic. The infection by 0. mangiferae, however, reduced the morning acidity in the leaf by about 35% and altered the normal acid fluctuation pattern. The overall results indicated that powdery mildew infection induces a range of disturbances to leaf metabolism, the most obvious being the activation of synthesis of new anthocyanins, degradation of chlorophyll-a and disturbance to malic acid metabolism.

Abstract. In this study, we investigated heavy metal uptake and the effects of Na 2 SiO 3 on heavy metal absorption by field grown Basella alba L (Basellaceae). The concentrations of Fe, Cr, Pb and Cd in the field soils were 29755.30 ± 292.02, 32.99 ± 0.97, 26.01 ± 1.02, 0.13 ± 0.004 µg/g, respectively. These concentrations are significantly below the maximum permissible limits reported by FAO/WHO. Although Fe, Cr, Pb and Cd were present in the soil, only Fe was absorbed by B. alba; the tissue concentrations of other heavy metals were below the detection limit. The distribution of Fe from soil to different plant parts was investigated by calculating transfer factors. Low transfer factors indicated low absorption and translocation of Fe from soil to plant tissue. We also investigated the effects of Na 2 SiO 3 on metal absorption by applying two different concentrations of Na 2 SiO 3 (Si-100 mg/L and Si-50 mg/L) alongside a control. There was a significant reduction of Fe absorption in B. alba treated with Si-100mg/L of Na 2 SiO 3 compared to that of plants treated with Si-50 mg/L of Na 2 SiO 3 and the control.