The essential oils of Thymus vulgaris L., of Eavandula R.C. hybrid and Mentha piperita L. were tested in vitro against the pathogenic fungi Rhizoctonia solani Kuhn, Pythium ultimum Trow var. ultimum, Eusarium solani (Mart.) Sacc, Colletotrichum tindemuthianum (Sacc. & Magn.) Briosi & Cav.Ali the oils tested inhibited fungal growth. The most effective oil was that of thyme, with a fungicidal activity attributable to thymol, found in a concentration of 50.06% in the oil tested. SEM observations revealed that these oils cause degeneration of the fungal hyphae which appeared emptied of their cytoplasmic content.
A study was made of the effects of garlic on the development of mycelium in the following phytopathogenic fungi: Fusarium solani (Mart.) Sacc., Rhizoctonia solani Kühn, Pythium ultimum Trow var. ultimum, and Colletotrichum lindemuthianum (Sacc. and Magnus) Briosi and Cav. A suspension of micronized garlic powder, which has volatile organic compounds mainly consisting of linear chain aldehydes, allyl sulfides and disulfides, was used for the trials. Mycelial development of the fungi was strongly inhibited at the maximum concentration of the aqueous extract tested (100 ml/liter); however only the growth of P. ultimum var. ultimum was entirely blocked. Transmission and scanning electron microscopy revealed cytomorphological alterations of the hyphae treated with garlic. R. solani and C. lindemuthianum hyphae appeared especially collapsed, while those of F. solani were less damaged, although thinner than the control hyphae. A general increase in vacuolization was also observed, with consequent reduction in the cytoplasm of the treated fungal cells. R. solani also revealed a thickening of the cell wall, whereas C. lindemuthianum revealed a singular accumulation of osmiophil bodies immediately under the cell membrane.
The antifungal activity of commercial Thymus vulgaris oils on the development of mycelium of the the phytopathogenic fungi Fusarium solani (Mart.) Sacc., Rhizoctonia solani Kühn and Colletotrichum lindemuthianum (Sacc. et Magn.) Briosi et Cav. was studied. The gas chromatography data showed that the essential oils were rich in thymol (22-38%) and its biogenetic precursors γ-terpinene and p-cymene. The carvacrol content was relatively low in all the oils tested, ranging between 1% and 2%. The fungicidal activity of the oils was correlated with their thymol content.The principal chemical components of thyme oils were then tested using the same concentrations as in the thyme oils. Only the fungicidal activity of thymol was high and close to that of the oils with the same thymol content. The effects of the thyme oils and thymol on the hyphae cytomorphology of the studied fungi was an increased vacuolization of the cytoplasm and accumulation of lipid bodies, undulations of the plasmalemma, and alterations of the mitochondria and endoplasmic reticulum.
Fourier transform Raman (FT Raman) and IR (FTIR) and (1)H-NMR spectroscopies coupled with differential scanning calorimetry (DSC) were applied to the characterization of root exudates from two cultivars of gladiolus (Spic Span and White Prosperity) with different degrees of resistance and susceptibility to Fusarium oxysporum gladioli, the main pathogen of gladiolus. This work was aimed at correlating the composition of root exudates with the varietal resistance to the pathogen. Spectroscopic analysis showed that White Prosperity root exudate differs from Spic Span root exudate by a higher relative amount of the aromatic-phenolic and sugarlike components and a lower relative amount of carbonylic and aliphatic compounds. DSC analysis confirmed the spectroscopic results and showed that White Prosperity root exudate is characterized by an aromatic component that is present in a higher amount than in the Spic Span root exudate. The results are discussed in relation to the spore germination tests showing that White Prosperity, which is characterized by a remarkable resistance toward F. oxysporum gladioli, exudes substances having a negative influence on microconidial germination of the pathogen; root exudates from Spic Span, one of the most susceptible cultivars to F. oxysporum gladioli, proved to have no effect. White Prosperity's ability to inhibit conidial germination of F. oxysporum gladioli can be mainly related to the presence of a higher relative amount of aromatic-phenolic compounds.
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