Ismail R. Abdel-Rahim

Bio: Ismail R. Abdel-Rahim is an academic researcher from Assiut University. The author has contributed to research in topics: Botrytis cinerea & Mycelium. The author has an hindex of 8, co-authored 16 publications receiving 232 citations.

Isolation of Trichoderma and Evaluation of their Antagonistic Potential against Alternaria porri

Abstract: Nine isolates of Trichoderma were collected from Assiut Governorate,Egypt, as leaf surface and endophytic fungi associated with onion florastalks. Four isolates were identified as Trichoderma harzianum, while fiveisolates were belonging to Trichoderma longibrachiatum. The antagonisticactivity of these isolates against onion purple blotch pathogen Alternariaporri was studied in vitro using dual culture assay. All tested Trichodermaisolates showed mycoparasitic activity and competitive capability againstthe mycelial growth of A. porri. Mycoparastic activity of Trichoderma wasmanifested morphologically by the overgrowth upon the mycelial growthof the pathogen and microscopically by production of coiling hyphaearound pathogen hyphae. Isolates of T. harzianum exhibited high abilityto compete on potato dextrose agar (PDA) medium causing the maximumrate of pathogen inhibition (73.12%), while isolates of T. longibrachiatumshowed inhibition rate equalling 70.3%. Chitinase activity of Trichodermawas assayed, and T. harzianum Th-3013 showed the maximum value con-tributing 2.69 U/min. Application of T. harzianum Th-3013 to control pur-ple blotch disease in vivo under greenhouse conditions caused diseasereduction up to 52.3 and 79.9% before and after 48 h of pathogen inocu-lation, respectively, while the fungicide Ridomil Gold Plus caused diseasereduction comprising 56.5 and 71.7%, respectively. This study proved thatT. harzianum Th-3013 as a biocontrol agent showed significant reductionin onion purple blotch disease compared with the tested fungicide.IntroductionPurple blotch disease, caused by Alternaria porri (Ellis)Cif., is one of the most serious diseases that wide-spread in many parts of the world, restricted to Alliumspp. and more prevalent in warm and humid environ-ments (Cramer 2000; Suheri and Price 2000). Purpleblotch disease caused significant reduction in bulband seed yield of the onion crop (Gupta and Pathak1988). The disease is more severe on seed crop ascompared to bulb crop causing sometimes 100% loos-ing of the seed production (Singh et al. 1992;Schwartz 2004). Although chemical control of onionblotch had been practised and its success depends lar-gely on high frequency of spraying, but today, thereare strict regulations on chemical fungicide use due tocarcinogenic effects, residual toxicity problems, envi-ronmental pollution and development of fungicide-resistant strains (Benitez et al. 2004; Rial-Otero et al.2005). Therefore, there are a large number of studiesthat have been devoted to apply a biological control asnature-friendly alternative method (Siameto et al.2010; Soria et al. 2012). The potential of Trichodermaspecies as biocontrol agents of plant diseases was firstrecognized in the early 1930s (Weindling 1932), andsince then, there have been extensive efforts in thecommercial production of them for disease control ina number of crops (Harman 1996; Gardener and Frav-el 2002). Recently, several investigation proved thatTrichoderma have been used to control many foliar

Assessment of protein silver nanoparticles toxicity against pathogenic Alternaria solani.

Abstract: Mycogenic synthesis of silver nanoparticles (AgNPs) was carried out in the present investigation using an aqueous extract of endophytic non-pathogenic Alternaria solani F10 (KT721914). The mycosynthesized AgNPs were characterized by means of spectroscopic and microscopic techniques. The surface plasmon resonance found at 430 nm confirmed the formation of stable AgNPs for several weeks at room temperature. Also, the results revealed the formation of spherical and monodispersed AgNPs with an average size of 14.8 ± 1.2 nm. The FT-IR spectrum suggested that the fungal extracellular proteins and secondary metabolites had the role in Ag reduction and AgNPs capping of which protein Ag nanoconjugates were formed. Furthermore, the mycosynthesized AgNPs exhibited potent antifungal activity against different pathogenic isolates of the same Alternaria solani fungus, the causal pathogen of tomato early blight disease. The antifungal efficiency of the AgNPs at 1, 5 and 10 ppm were evaluated for 8 days after incubation by measuring the inhibition rate of fungal radial growth. The results were further supported by investigating fungal hyphae morphology alteration by scanning and transmission electron microscopy. Treated fungal hyphae showed formation of pits and pores. Also, the mycosynthesized AgNPs were able to pass and distribute throughout the fungal cell area and interact with the cell components.

Leaf surface and endophytic fungi associated with onion leaves and their antagonistic activity against Alternaria porri.

Abstract: Sixty-eight fungal species belonging to 29 genera were isolated as leaf surface and endophytic fungi from healthy and purple blotch diseased onion leaves. The fungal populations associated with diseased onion leaves (1.360 × 10 CFU/g leaf in the phyllosphere, 2.614 CFU/leaf segment in the phylloplane and 1.324 CFU/leaf segment in the surface-sterilised diseased leaves) were higher than those in healthy samples (0.804 × 10 CFU in the phyllosphere, 1.184 CFU in the phylloplane, and 0.35 CFU as endophytes). Endophytic fungi of healthy leaves were represented by 12 genera and 15 species, while fungi of surface-sterilised diseased leaves included 17 species from 13 genera. The mycobiota associated with surface-sterilised diseased leaves were different from the endophytic fungi of healthy samples, whereas the disease may stimulate colonisation of opportunistic fungi causing secondary infections such as Botrytis cinerea, Penicillium aurantiogriseum, Alternaria alternata and Cladosporium spp. In contrast, healthy leaves were a source of antagonistic endophytic fungi such as Trichoderma harzianum and T. koningii. Testing the antagonistic effect of 91 fungal isolates against Alternaria porri showed that nine isolates of Trichoderma produced the highest suppressive potential (73.1%) depending on competition and mycoparasitism. Epicoccum nigrum and Penicillium oxalicum exhibited antibiosis against A. porri producing a 12 mm broad inhibition zone. In conclusion, the quantitative and qualitative compositions of fungi associated with onion leaves were distinctly influenced by A. porri infection. Mycobiota associated with asymptomatic onion leaves such as Epicoccum nigrum, Penicillium oxalicum and Trichoderma harzianum are a natural source of eco-friendly bioagents. They showed an effective antagonistic potential against A. porri, and may thus be applied as an alternative to fungicides.

Fungicidal activity of extracellular products of cyanobacteria against Alternaria porri

Abstract: Although cyanobacteria are recognized as renewable sources of biomass for bioactive compounds, they have received little attention as potential biocontrol agents of foliar plant diseases. The purpose of this study was to evaluate the fungicidal efficacy of cyanobacterial extracellular products against Alternaria porri, which causes onion purple blotch disease, in vitro and under greenhouse conditions. Among the tested cyanobacteria (Anabaena oryzae, Arthrospira sp., Nostoc minutum, N. muscorum and Oscillatoria sp.), extracellular metabolites of N. muscorum and Oscillatoria sp. reduced the linear growth of A. porri by 20.37 and 36.34%, respectively. Culture filtrates of both Oscillatoria sp. and N. muscorum contained high concentrations of phenolic compounds (104.33 and 145.0 mg l−1, respectively), and alkaloids (473.31 and 378.12 mg l−1, respectively). GC-Mass analysis revealed that the most prevalent component in culture filtrates of N. muscorum and Oscillatoria sp. was beta ionone (7.21 and 7.17...

Quantification of biofilm in microtiter plates: overview oftesting conditions and practical recommendations for assessmentof biofilm production by staphylococci.

Abstract: The details of all steps involved in the quantification of biofilm formation in microtiter plates are described. The presented protocol incorporates information on assessment of biofilm production by staphylococci, gained both by direct experience as well as by analysis of methods for assaying biofilm production. The obtained results should simplify quantification of biofilm formation in microtiter plates, and make it more reliable and comparable among different laboratories.

The Estimation of the Bactericidal Power of the Blood. With a Note by J. O. IRWIN.

Abstract: The survival rate, p , of a measured inoculum of Staph. aureus in a standard volume of denbrinated blood, is a reliable quantitative measure of the bactericidal power of blood. The number of viable organisms in the inoculum and in the blood-bacterium mixture may be estimated with the necessary accuracy by counts of colonies developing from measured volumes of the fluids let fall on to the surface of solid media. Fildes' agar was the most suitable medium for this surface-viable count, and was selected on the basis of four criteria; of the media tested it yielded the highest counts, and the counts conformed most closely to a Poisson series; and on it the mean colony size was maximum, and the coefficient of variation of colony size was minimum. On this medium, the close conformity of the separate count values to a Poisson series enabled the standard error of the survival rate to be determined from a simplification of the general expression for the standard error of a ratio. The number of colonies growing from a sample of a blood-bacterium mixture may be reduced, not by killing of the individual cocci, but as a result of their aggregation either by agglutinins in the blood, or in the cytoplasm of leucocytes that are phagocytic but not bactericidal. It appears that these mechanisms are unlikely to operate in blood-bacterium mixture containing relatively few organisms; in such mixtures the survival rate is a reflexion of the killing power only. The immunological significance of p has not been investigated, but the range of values for healthy human adults differs significantly from that for sufferers from chronic staphylococcal infection. Moreover, by the technique employed differences may be detected between individual values of p that cannot reasonably be attributed to technical or sampling errors.

Characterization of Novel Trichoderma asperellum Isolates to Select Effective Biocontrol Agents Against Tomato Fusarium Wilt.

Abstract: The use of novel isolates of Trichoderma with efficient antagonistic capacity against Fusarium oxysporum f. sp. lycopersici (FOL) is a promising alternative strategy to pesticides for tomato wilt management. We evaluated the antagonistic activity of 30 isolates of T. asperellum against 4 different isolates of FOL. The production of extracellular cell wall degrading enzymes of the antagonistic isolates was also measured. The random amplified polymorphic DNA (RAPD) method was applied to assess the genetic variability among the T. asperellum isolates. All of the T. asperellum isolates significantly reduced the mycelial growth of FOL isolates but the amount of growth reduction varied significantly as well. There was a correlation between the antagonistic capacity of T. asperellum isolates towards FOL and their lytic enzyme production. Isolates showing high levels of chitinase and β-1,3-glucanase activities strongly inhibited the growth of FOL isolates. RAPD analysis showed a high level of genetic variation among T. asperellum isolates. The UPGMA dendrogram revealed that T. asperellum isolates could not be grouped by their anta- gonistic behavior or lytic enzymes production. Six isolates of T. asperellum were highly antagonistic towards FOL and potentially could be used in commercial agriculture to control tomato wilt. Our results are consistent with the conclusion that understanding the genetic variation within Trichoderma isolates and their biochemical capabilities are required for the selection of effective indigenous fungal strains for the use as biocontrol agents.