Silicon amendments to soil have resulted in a decrease of diseases caused by several soilborne pathogens affecting a wide number of crops. This study evaluated the physiological and biochemical mechanisms that may have increased resistance of banana to Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense, after treatment with silicon (Si) amendment. Plants from the Grand Nain (resistant to F. oxysporum f. sp. cubense) and "Maçã" (susceptible to F. oxysporum f. sp. cubense) were grown in plastic pots amended with Si at 0 or 0.39 g/kg of soil (-Si or +Si, respectively) and inoculated with race 1 of F. oxysporum f. sp. cubense. Relative lesion length (RLL) and asymptomatic fungal colonization in tissue (AFCT) were evaluated at 40 days after inoculation. Root samples were collected at different times after inoculation with F. oxysporum f. sp. cubense to determine the level of lipid peroxidation, expressed as equivalents of malondialdehyde (MDA), hydrogen peroxide (H(2)O(2)), pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids), total soluble phenolics (TSP), and lignin-thioglycolic acid (LTGA) derivatives; the activities of the enzymes phenylalanine ammonia-lyases glucanases (PALs), peroxidases (POXs), polyphenoloxidases (PPOs), β-1,3-glucanases (GLUs), and chitinases (CHIs); and Si concentration in roots. Root Si concentration was significantly increased by 35.3% for the +Si treatment compared with the -Si treatment. For Grand Nain, the root Si concentration was significantly increased by 12.8% compared with "Maçã." Plants from Grand Nain and "Maçã" in the +Si treatment showed significant reductions of 40.0 and 57.2%, respectively, for RLL compared with the -Si treatment. For the AFCT, there was a significant reduction of 18.5% in the +Si treatment compared with the -Si treatment. The concentration of MDA significantly decreased for plants from Grand Nain and "Maçã" supplied with Si compared with the -Si treatment while the concentrations of H(2)O(2) on roots and pigments on leaves significantly increased. The concentrations of TSP and LTGA derivatives as well as the PALs, PPOs, POXs, GLUs, and CHIs activities significantly increased on roots of plants from Grand Nain and "Maçã" from the +Si treatment compared with the -Si treatment. Results of this study suggest that the symptoms of Fusarium wilt on roots of banana plants supplied with Si decreased due to an increase in the concentrations of H(2)O(2), TSP, and LTGA derivatives and greater activities of PALs, PPOs, POXs, GLUs, and CHIs.

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense, is a disease that causes large reductions in banana yield worldwide. Considering the importance of silicon (Si) to potentiate the resistance of several plant species to pathogen infection, this study aimed to investigate, at the histochemical level, whether this element could enhance the production of phenolics on the roots of banana plants in response to F. oxysporum f. sp. cubense infection. Plants of cultivar Maçã, which is susceptible to F. oxysporum f. sp. cubense, were grown in plastic pots amended with 0 (-Si) or 0.39 g of Si (+Si) per kilogram of soil and inoculated with race 1 of F. oxysporum f. sp. cubense. The root Si concentration was increased by 35.6% for +Si plants in comparison to the -Si plants, which contributed to a 27% reduction in the symptoms of Fusarium wilt on roots. There was an absence of fluorescence for the root sections of the -Si plants treated with the Neu and Wilson's reagents. By contrast, for the root sections obtained from the +Si plants treated with Neu's reagent, strong yellow-orange fluorescence was observed in the phloem, and lemon-yellow fluorescence was observed in the sclerenchyma and metaxylem vessels, indicating the presence of flavonoids. For the root sections of the +Si plants treated with Wilson's reagent, orange-yellowish autofluorescence was more pronounced around the phloem vessels, and yellow fluorescence was more pronounced around the metaxylem vessels, also indicating the presence of flavonoids. Lignin was more densely deposited in the cortex of the roots of the +Si plants than for the -Si plants. Dopamine was barely detected in the roots of the -Si plants after using the lactic and glyoxylic acid stain, but was strongly suspected to occur on the phloem and metaxylem vessels of the roots of the +Si plants as confirmed by the intense orange-yellow fluorescence. The present study provides new evidence of the pivotal role of the phenylpropanoid pathway in the resistance of banana plants to F. oxysporum f. sp. cubense infection when supplied with Si.

Target spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado. Information in the literature regarding the biochemical defence responses of soybean to C. cassiicola infection is rare. Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot. The activities of chitinases (CHI), b-1-3-glucanases (GLU), phenylalanine ammonia-lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin-thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar. The target spot severity, number of lesions per cm 2 of leaflet and area under the disease progress curve were significantly lower for plants from cv. FUNDA-CEP 59 compared to plants from cv. TMG 132. The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C. cassiicola. Inoculated plants from cv. FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv. TMG 132. In conclusion, the results of this study demonstrated that the defence-related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied. The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C. cassiicola infection were highly associated with soybean resistance to target spot.

This study aimed to determine the effect of silicon (Si) in reducing the symptoms of Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), on banana plants. Banana seedlings of Grand Nain (resistant) and Mac¸a˜(susceptible) were grown in plastic trays amended with 0 (ÀSi) or 0.39 g Si (+Si) per kg of soil and inoculated with Foc at 60 days after transplanting. The Si concentration in the roots and rhizome-pseudostem significantly increased by 30.26 and 58.82%, respectively, for the +Si treatment compared with ÀSi treatment. The Si concentration in the roots and rhizome-pseudostem of Grand Nain plants was, respectively, 11.57 and 37.04% greater than that found in Mac¸a˜. The +Si plants showed a reduction of 12.37, 49.81, 51.87 and 20.39%, respectively, for the area under reflex leaf symptoms progress curve, the area under root symptoms progress curve, the area under disease progress curve and the area under asymptomatic fungal colonization of tissue progress curve compared with -Si plants. The area under darkening of rhizome-pseudostem progress curve (AUDRPPC) of Mac¸a˜significantly increased by 15.98% for the ÀSi treatment in comparison with the +Si treatment. For the +Si treatment, the AUDRPPC of the plants from the Mac¸a˜cultivar significantly decreased by 20.59% in comparison with the plants from the Grand Nain cultivar. The area under relative lesion length progress curve (AURLLPC) of the plants from the Mac¸a˜cultivar significantly decreased by 41.54% for the +Si treatment in comparison with the ÀSi treatment. There was no significant difference between the -Si and +Si treatments in the AUDRPPC and AURLLPC of Grand Nain. For the +Si treatment, the AURLLPC of Grand Nain significantly decreased by 9.23% in comparison with Mac¸a˜. There was no significant difference between the Grand Nain and Mac¸af or the AUDRPPC and AURLLPC in the ÀSi treatment. The findings of this study show that supplying Si to banana plants, especially to a susceptible cultivar to Foc, had a great potential in reducing the intensity of Fusarium wilt and may play a key role in disease management when banana plants are cultivated in Si-deficient soils infested by this pathogen.

Blast, caused by Pyricularia oryzae, has become a significant disease threat to wheat (Triticum aestivum L.) in Brazil. This study aimed to investigate at the histochemical level if silicon (Si) could enhance the production of flavonoids in the leaves of wheat plants in response to P. oryzae infection. Plants from the Aliança cultivar, which are susceptible to blast, were grown in hydroponic cultures containing 0 (-Si) or 2 mM of Si (+Si) and inoculated by spraying a conidial suspension of P. oryzae (1 × 10 5 conidia mL ). This increased Si concentration was correlated with reduced fungal growth inside the epidermal cells and the development of blast symptoms on leaves. Strong fluorescence, which is an indication of the presence of flavonoids, was detected in the leaf cells of +Si plants usingNeu's and Wilson's reagents. A novel item of evidence is that, at the histochemical level, Si is involved in the potentiation of the biosynthetic pathway of flavonoids that increases wheat resistance to blast.