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Long term investigations revealed that cultivation of strawberries (Fragaria magna Thuill.) for 10 years continuously in one plot reduces their vitality: the number of the produced runners decreases by 41%, of leaves – by 30%, form only 28% of inflorescence, the yield reduces by 50% in comparison with strawberries grown for two years in a new plot. Evident decline in the vitality and productivity of strawberries was detected during 4th–6th years of cultivation. Unequal reaction of the tested cultivars upon the durability of cultivation was noticed; strawberries of the cultivar ‘Senga Sengana’ reacted slightly, while the ones of the cultivar ‘Nida’ – strongly. It is related with different sensibility of these cultivars towards the disease agents of root rots. It was determined that long-term cultivation of the Fragaria genus plants results in the accumulation of the parasitic fungi propagules in soil: Ascochyta fragaricola, Cercospora fragariae, Fusarium oxysporum, F. solani, Perenospora fragariae, Phytophthora cactorum, Pythium intermedium, P. ultimum, Plasmodiophora brassicae, Sclerotium rolfsii, Verticillium alboatrum. Therefore, cultivation of strawberries in the same plot for longer time increases the phytopathogenic potential of soil, and short interval (1–2 years) between planting has little significance upon it. The second reason for low productivity of strawberries cultivated for a long in one plot is soil tiredness caused by fungi, synthesising and excreting into surrounding toxic secondary metabolites, widespread in the rhizosphere, especially those belonging to the Penicillium genus: P. janthinellum, P. verruculosum var. verrucosum, P. canescens, P. spinulosum.
The aqueous extracts of leaf of Citrus aurantifolia L were assessed in vitro for inhibitory activity against Macrophomina phaseolina isolated from dry root rot specimens of Gingelly. The antifungal activity was determined by poison food technique. The extracts have shown dose dependent inhibition of mycelial growth of test fungi. The extracts were more effective in inhibiting Macrophomina phaseolina. The extracts of Citrus aurantifolia were found effective against Gingelly dry root rot pathogens. Further field experiments are to be carried out to recommend the extracts against the disease.
Fungicidal properties of 4-(1,3,4-thiadiazol-2-yl)benzene-1,3-diols set under in vitro conditions against five phytopathogenic fungi have been evaluated. The substitution panel includes amino-, alkyl-, alkoxyl-, aryl- and heteroarylderivatives. The most active compound with the benzyl substituent exhibits fungistatic effects amounting to 90-100% with the concentration of 20 μg mL-1 against R. solani, similar to the standard fungicides. The derivatives with amine moiety generally display lower activity than other analogues. F. culmorum seems to be the most refractory fungus compared to studied compounds. The influence of substitution of C-5 at the constant fragment at C-2 of 1,3,4-thiadiazole ring on the antifungal effect is discussed. To explain differences in the activity the quantum-chemical calculations were made.
Several species of Solanum produce secondary metabolites with antimicrobial activity. In the present study, the inhibitory activity of Solanum chrysotrichum, S. erianthum, S. torvum and S. rostratum against phytopathogenic Curvularia lunata was determined. Methanol extracts from roots, stems, leaves and fruits were evaluated by the method of mycelial inhibition on agar and the minimum inhibitory concentration (MIC) was determined on a liquid medium. To increase the antimicrobial activity, the combined activity of the most active extracts for each phytopathogen was also determined (a combination of intra and interspecies extracts). The results showed that 12 of the 16 methanolic extracts of Solanum species had antifungal effects against C. lunata. The extracts of S. rostratum and S. erianthum developed the highest activity (~80% inhibition and 28.4 MIC μg . ml–1), even, equal to or greater than, the reference fungicide. The mixture of the active extracts of S. chrysotrichum and S. torvum increased their activity. Various extracts affected the macro and microscopic morphology and most of them reduced the number of conidia of the fungus. This resulted in the capacity to control the vegetative growth and reproduction of C. lunata, the causal fungus of corn leaf spot disease.
Stem canker of brassicas is one of the most damaging diseases of oilseed rape worldwide. The disease is caused by two related Leptosphaeria species, and L. maculans is regarded as the more damaging one. Being an ascomycete, the pathogen is able to quickly create new variants that can overcome new resistance genes introduced by researchers and breeding companies. The aim of this work was to study polymorphism of L. maculans populations using 10 recently developed minisatellite markers. The studied subpopulations differed with metconazole treatment. Seven minisatellite markers showed polymorphisms and formed alleles varying from 2 to 10 different core motifs, with 5 alleles on average. In total 36 alleles were found. The majority of alleles (72%) were found in both studied subpopulations of L. maculans. There were 28 alleles in the group of L. maculans isolates originating from plants not treated with any fungicide and 32 in the subpopulation treated with metconazole. Ten unique alleles and imbalanced ratios between some alleles contributed to differences between L. maculans subpopulations. The minisatellites MinLm555, MinLm935-2, MinLm939, MinLm1139 and MinLm2451 showed 6 new variants as compared to the isolates described so far.
The quantitative and qualitative composition of the soil microorganisms depends, amongst others, on whether monoculture or crop rotation is applied. The main phytopathogen infecting flax (Linum usitatissimum L.) is the Fusarium genus as well as fungi of the Alternaria, Phoma, Botrytis, Verticillium, Rhizoctonia genera, however soil hyperparasites of the Trichoderma genus can control them successfully. Both types of microorganisms were isolated from the roots sampled both from monocuture and crop rotation and from plants in emergence and flowering stage. The enzymatic activity was researched for a variety of nutrient substrates (cellulose, pectin, starch, protein) as well as the capacity for dissolving triphosphates. There was also investigated the extent of Trichoderma fungal antagonistic activity towards pathogens.
Leaf spot disease in potato is caused by Alternaria alternata (Fr.) Keissler, an opportunistic pathogen that infests many agricultural crops worldwide in the field and during postharvest storage of vegetables and fruits. Alternaria alternata is associated with leaf spot disease in potato in Iran. Thus, there is a need to investigate the virulence and genetic variability of Iranian A. alternata isolates to facilitate the development of appropriate management strategies. In the present study, we analyzed a total of 28 isolates obtained from the main potato-growing regions of Iran, including the Ardebil, Hamedan, Isfahan, and Fars provinces. The pathogens were characterized based on sequence analysis of the genes encoding glyceraldehyde-3-phosphate dehydrogenase (gpd), plasma membrane ATPase, Alternaria allergen a 1 (Alt a1), calmodulin, and actin. In addition, random amplified polymorphic DNA (RAPD), intersimple sequence repeat (ISSR), and virulence studies were performed. Phylogenetic analysis of the combined dataset indicated that the five representative isolates were grouped with the subcluster comprising A. alternata. RAPD and ISSR analyses clustered the 28 A. alternata isolates into different groups with no correlation with their corresponding geographical origins. Results of the pathogenicity assay indicated that all A. alternata isolates were pathogenic against potato. However, the A. alternata isolates showed high variability in terms of virulence.
The antifungal activities of ethanolic extracts of three Saudi plants; camel thorn (Alhagi maurorum Medic.), caper (Capparisspinosa L.), and pomegranate (Punica granatum L.) were investigated in vitro against Alternaria alternata, Fusarium oxysporum, Phomadestructiva, Rhizoctonia solani, and Sclerotium rolfsii at concentrations of 0, 3, 6, and 9% (v/v). All tested plant extracts; seeds, roots, and rinds had different degrees of antifungal activity against the tested fungi. When compared with the control, the highest antifungal activity was recorded for camel thorn seeds extract at a concentration of 9%, while, pomegranate rinds extract at 9% came in second. Camel thorn rinds extract came in last even when used at a high concentration. The ethanolic extract of camel thorn seeds may be recommended as a potent bio-fungicide. Extensive studies should be undertaken for the ethanolic extract of camel thorn seeds as a strong antifungal agent against fungal plant diseases.
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