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The fungicidal effect of some essential oils against Alternaria solani one of the species that cause early blight of potato was evaluated under in vitro and field conditions. Effect of carnation, caraway, thyme oils and the chemical fungicide Ridomil MZ 72 at various concentrations on mycelial growth of A. solani was tested. Carnation oil had the strongest and most extensive inhibitory effect on fungal growth. Slightly less effective were caraway and thyme oils followed by the chemical fungicide. Extended field trails for two cultivation seasons proved that the application of essential oils twice as foliar spray had a superior effect to the fungicide treatment for reducing the early blight incidence comparing with untreated control. An opposite relationship between the disease incidence and concentrations of applied essential oils was observed. The increase in potato yield also followed the same trend. The highest reduction in disease incidence and yield increase was recorded in treatments with 1% of carnation, caraway and thyme oils in descending order. Ridomil MZ 72 applied at the dose recommended by manufactories had a low effect in this regard. Essential oils treatments might be used as easily applied, safe and cost effective control methods against such plant diseases.
The antifungal effect of twenty powdered spice plants and their extracts at concentrations of 2, 4,8 and 1, 3, 6%, respectively was evaluated in relation to the radial mycelial growth of various soilbome fungi causing damping-off disease. The spice powder or extract were added to the culture medium PDA to obtain the proposed concentrations. Concentration of 8% of powdered spices and 6% of their extracts were able to cause complete growth inhibition of major tested fungi. High significant inhibitory effect on radial fungal growth was observed for different concentrations of carnation (Dianthus caryophyllus), cinnamon (Cinnamomum burmannil), garlic (Allium sativum) and thyme (Thymus vulgaris). Meanwhile, fennel (Foeniculum vulgare), marjoram (Origanum majorana) and chamomile (Matricaria hamomilla) showed a low inhibitory effect on tested fungi. Moderate inhibitory effect was observed with the other tested spices. In the greenhouse, efficacy of spice plants as powder or their extracts in addition to the fungicide Rizolex-T used as seed dressings against faba bean damping-off incidence was evaluated in pot experiment using soil artificially infested with the disease agents (Fusarium solani and Rhizoctonia solani). Spice extracts showed superior reducing effect on damping-off disease incidence at pre-emergence growth stage to that of powder treatments and Rizolex-T as well, while an opposite effect was observed at post-emergence growth stage. Carnation and cinnamon spices showed the highest protecting effect against disease incidence when applied as powder or extracts. It is interesting to note that spice plants as powder or extracts gave a similar effect to the fungicide Rhizolex-T in reducing damping-off incidence either at pre- or post-emergence stages of faba bean growth. Promising applicable technique could be suggested in the light of the results obtained. The use of spice plants as powder or extract for seed dressing might be considered as safe, cheep and easily applied method for controlling soilbome plant pathogens considering the avoidance of environmental pollution and the side effect of pesticide application.
In Egypt, Chinese cabbage Brassica rapa var. pekinensis is a recently introduced as a winter crop grown throughout the country along the Nile valley as well as in new reclaimed lands. Pythium rot of Chinese cabbage was detected during the cultivation season 2005/2006 at four governorates throughout the north side of Egypt. Isolation trails revealed that Pythium ultimum was the causal organism of disease incidence. The cultivar of Chinese cabbage Napa (green) showed higher susceptibility to infection than Michihli cv. (red). Trichoderma harzianum, T. viride, Bacillus subtilis and Pseudomonas fluorescens isolated from the rhizosphere of healthy Chinese cabbage could inhibit the in vitro growth of P. ultimum at different degrees. Under greenhouse and field trails, applying of biocontrol agents as a combination of soil mixing plus root dipping method was generally more effective than each method applied individually for suppressing Pythium rot incidence followed by soil mixing and root dipping methods. The applied bioagents could be arranged according to their activity for suppressing the disease incidence as follows: T. harzainum, B. subtilis, T. viride and P. fluorescens, respectively. The use of biocontrol agents as soil mixing and root dipping treatments could provide additional protection against crop loss due to Pythium rot disease.
Broomrapes (Orobanche spp.) are important parasitic weeds of peas, faba bean and tomatoes and other winter crops in Egypt. They are widespread and are major factors limiting production of these crops. From an extensive survey of Egyptian soils naturally infested with broomrapes, 42 isolates of fungi belonging to genera of Alternaria, Fusarium and Trichoderma were identified as pathogens of broomrapes under laboratory and greenhouse conditions. Three isolates of Trichoderma spp. including T. harzianum T1, T. harzianum T3 and T. viride T2 were further tested for control of Orobanche spp. in peas, faba bean and tomatoes under field conditions. Results of field studies showed that soil treatment with these three fungal agents alone or soil treatment with fungal agents plus aerial spray of glyphosate (50 ppm) was effective in reducing infection of broomrapes and increasing yields of peas, faba bean and tomatoes. The prospect of developing T. harzianum T1, T. harzianum T3 and T. viride T2 as mycoherbicides for control of bromerapes of peas, faba bean and tomatoes in Egypt is discussed in this paper.
The effects of caraway and peppermint extracts was evaluated at concentrations of 2, 4, 6, 8 and 10%, respectively on the radial mycelial growth of Sclerotium rolfsii. High significant inhibitory effect on radial fungal growth was observed with different concentrations of each of plant extracts. Concentration of 6% and more of the two extracts in combination were able to cause complete growth inhibition of the tested fungus. In greenhouse, the efficacy of plant extracts in addition to the fungicide Rizolex-T as seed dressing on pea root rot incidence was evaluated in pot experiment using soil artificially infested with the disease agent. All treatments showed a significant reduction in disease incidence compared with the control treatment. Rizolex-T followed by combination of caraway and peppermint extracts as a mixture showed superior reduction effect on root rot disease incidence at pre-, and post-emergence growth stages than individual treatment with each of extracts. The usage of caraway and peppermint extracts for seed dressing before sowing might be applied as control measure for controlling root rot diseases.
The suppressive effect of sodium and calcium salts applied individually or combined with the yeast Saccharomyces cerevisiae against Alternaria solani the causal agent of early blight disease of potato was evaluated under laboratory, greenhouse and field conditions. In vitro test a complete inhibition in fungal growth was observed at concentration of 30 mg/ml of both sodium bicarbonate and calcium chloride. The commercial backing yeast S. cerevisiae (CBY) enhanced the inhibitory effect of tested salts reflected in increasing mycelial fungal growth reduction when combined at the rate of 1:1 at each concentration tested. In pot experiment, under artificial infestation with pathogenic fungus, application of sodium bicarbonate or calcium chloride significantly reduced the early blight incidence and severity by increasing their concentrations. Their most effective concentration were 30 mg/ml that reduced the disease incidence by 50 and 62.4%, respectively. Superior effect of sodium bicarbonate or calcium chloride in disease reduction was observed when they combined with CBY. Field trails for evaluating the most promising greenhouse treatments were preformed under natural infestations during two successive summer seasons. Calcium chloride proved higher efficacy for reducing both disease incidence and severity than that of sodium bicarbonate when applied either alone or combined with CBY. Also, it is observed that increasing concentrations of both sodium bicarbonate or calcium chloride showed parallel decrease in disease incidence and severity. Application of (CBY) enhanced the efficacy of salts spraying against early blight disease. Similar trend was also observed with the increase of potato tubers yield. On the light of the present study it could be suggested that the usage of combined application of the yeast S. cerevisiae with sodium bicarbonate or calcium chloride might be used as easily applied, safely and cost effective control methods against such plant diseases.
Essential oils from four plants, i.e. geranium, rosa, lemon and mint were tested for their activity in vitro and in vivo against Rhizoctonia solani and Fusarium oxysporum f. sp. phaseoli, the cause of root rot and wilt of beans. In vitro, they were found to have an inhibitory effect against the mycelial growth of R. solani and F. oxysporum f. sp. phaseoli. Complete inhibition in fungal growth was observed at a concentration of 4% of each essential oil and Topsin M at 400 ppm as well. In greenhouse the four essential oils were tested as seed coating and/or foliar spray. Results of seed coating at a concentration of 1% clearly demonstrate a good protection of emerged bean seeds against invasion of R. solani and F. oxysporum f. sp. phaseoli compared with the fungicide treatment. A similar trend was observed in a lower extent when the essential oils were applied as bean seeds coating followed by seedlings foliar spray under field conditions. Obvious yield increase as bean green pods, in all treatments, was significantly higher than in the control.
Control measures of postharvest diseases of strawberry and navel orange fruits using hydrogen peroxide, calcium chloride and chitosan were evaluated under in vitro and in vivo conditions. All tested concentrations of chemicals used were able to reduce the linear growth and spore germination of B. cinerea; R. stolonifer; P. digitatum and P. italicum. Complete inhibition of linear growth and spore germination was obtained with concentrations of 1.5 and 2.0% of all treatments. Under storage conditions, significant reduction in descending order of mould incidence was observed in strawberry and orange fruits treated with ascending concentrations of calcium chloride, hydrogen peroxide and chitosan. Obtained data revealed significant reduction in mould incidence in fruits when treated by calcium chloride and chitosan 12h before artificial inoculation with the mould pathogens, while hydrogen peroxide showed the opposite result. The present study demonstrated that the application of hydrogen peroxide is superior to treatment with calcium chloride or chitosan enhanced the control activity against mould pathogens which as it expressed was as either percentage of diseased fruits or decay development as rotted tissue weight of strawberry and navel orange. The applied tested chemical might act as contact and systemic fungicides which have a protective or therapeutic effect.
Postharvest diseases caused by Geotricum candidum (sour rot), Penicillium digitatum (green mould), and P. italicum (blue mould) are the most important negative factors affecting handling and marketing of citrus fruits in Egypt. A new formula containing stevia leaf powder and a mixture of the three commercial chemical active ingredients: ketoconazole, fluconazole, and itraconazole has been successfully applied. Either chitosan or water wax were used as carriers, against fruit mould pathogenic fungi under laboratory and storage conditions. Results of the in vitro test showed that a complete reduction in linear fugal growth was observed when the ingredients of the new formula were used individually at a concentration of 400 μg/ml each, while a mixture of all the tested chemicals had a superior effect with all fungal growth completely inhibited with the use of the mixture at a concentration of 100 μg/ml. Similar results were recorded on citrus fruits which were coated with the suggested formula of chitosan or wax containing chemical compounds as a semi applicable technique using navel orange peel discs. Furthermore, the obtained results were confirmed using in vivo testing on navel orange and lime fruits, under artificial inoculation conditions of the pathogenic fungi within a storage period extended for four weeks. The proposed approach provides the treated agricultural products with long acting protection against microbial invasion and even association. This formula could be used as a fungicide alternative for protecting the agricultural products which have high moisture contents. The formula can be used against mould pathogens to prolong the healthy shelf life of the agricultural products. Such a treatment is safe, cheap, easily applied, and without residues which are harmful to people and the environment.
Carnation, caraway, thyme, peppermint and geranium essential oils have been found to have inhibitory effects against the mycelial growth of Fusarium solani, Rhizoctonia solani, Sclerotium rolfsii and Macrophomina phaseolina under in vitro conditions. Complete inhibition of fungal growth was observed with the use of 4% carnation and geranium oils. Mycelial growth of the tested fungi showed more sensitivity to high concentrations of thyme than to caraway and peppermint oils. Moreover, essential oils used to coat seeds resulted in a significant reduction of root rot incidence of bean, at both pre- and post-emergence stages under greenhouse conditions. Under field conditions seeds coated with essential oils at a concentration of 4% sown in soil treated with the bio-agent Trihoderma harzianum, gave pronounced protection to emerged bean seeds against the invasion of root rot pathogenic fungi. Compared to the control, the above treatment resulted in a reduction of disease incidence at the pre-emergence stage. This reduction was calculated to be between 47.3 and 55.4% compared with a 16.1% reduction with the use of the Rizolex-T treatment. At the post-emergence stage, all applied treatments were able to reduce the percentage of root-rot incidence. Reduction ranged between 41.4 and 47.1% over the untreated control. Reduction in disease incidence was reflected in a yield increase of 15.1-28.8% and 40.1-50%, in seeds coated with one of the different essential oils, or combined with T. harzianum soil treatments, in the respective order. Seeds coated with the fungicide Rhizolex-T caused a yield increase estimated as 11.3% over the check treatment. These results show that application of essential oils in integration with the bio-agent T. harzianum may be considered as an applicable, safe and cost-effective method for controlling such soilborne diseases.
The efficacy of applying biocontrol agents, chemical fungicide and nematicide as protective treatments against the soilborne parasites, Fusarium spp. (Fusaria) and citrus nematode Tylenchulus semipenetrans Cobb was evaluated. The experiment took place under field conditions in a citrus orchard cultivated with 16-year-old sweet orange (Citrus sinensis L.) osbech cv. Valencia trees grafted on sour orange (C. aurantium L.) rootstock during the growing season November 2006/ October 2007. This orchard is located at Bader district, Behera governorate, Egypt. The populations of soil fauna and flora under trees canopy were examined just before treatment, and 1, 3, 6, 9 and 12 months after the treatment application. A visual inspection for the appearance of symptoms related to Fusarium or nematode infection on treated and untreated citrus trees was carried out periodically every two weeks throughout the experimental period. The populations of Fusarium spp. were gradually decreased throughout the experimental period. However, the antagonistic bacterial isolates showed drastic effect for reducing the Fusaria population from 38.5% before treatments to a range of 1.2–4.0% after one month of such a bacterial application followed by the Kocide (fungicide) treatment which recorded 6.6%. Meanwhile, Fusaria populations of 18.4 and 16.3% were recorded as Fusaria population in treatments of the nematicide Carbofuran and entompathogenic nematode, respectively. Also, the population density of T. semipenetrans juveniles drastically decreased soon after all the treatment applications. Then after the nematode population build up during the growing season followed a natural distribution decline shape starting from the third month of application up to the ninth month, then it decreased. The citrus nematode increased steadily in the untreated check till September 2007 then its population level decreased. Treatments of Bacillus subtilis – B (20 ml) and Pseudomonas fluorescens (20 ml) gave the highest citrus yield followed by B. subtilis A (10 ml); B. subtilis B (10 ml) and Kocide (fungicide). Moreover, citrus trees treated with B. subtilis A (10 ml); P. fluorescens (10 ml) and Carbofuran (nematicide) had a higher yield production than trees treated with entomopathogenic nematodes Heterorhabditis egyptii (Abd-Elgawad and Ameen 2005). Yet, visual monitoring for disease incidence throughout the citrus orchard during the whole period of the study revealed no disease symptoms of any fusaria or nematode infection in treated trees. Untreated trees had a 1.9 and 3.1% fusaria and nematode infection, respectively. The importance of the present work, therefore, is based on the proposed bioagents as protective applications that are able to inhibit the citrus pathogens and prevent them from causing citrus damage.
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