Production of cytochalasin B by Helminthosporium solani under different culture conditions and its effect on the mitosis of onion root cells

The optimum temperature for maximum production of cytochalasin B [CB] by Helminthosporium solani was 30°C. The optimum pH value was 5.5 - 6.0, and the maximum CB production was attained after nine days of incubation. Glucose and sodium nitrate were the best carbon and nitrogen sources for CB production. CB at the concentration of 30 microg/ml decreased the mitotic index [MI%] of Allium cepa L. [onion, Giza, 20] roots from 8.42 to 4.83%. The spindle constituents [microtubules] were affected in a way that gave rise to a number of chromosomal abnormalities, namely; stickiness, un-oriented, bridges, free and distributed spindles without multinucleated cells production. CB at this concentration decreased onion seed production by 5.7% compared with the control. CB also induced morphological changes to roots and decreased the root length

Use of the RAPD-PCR technique to fingerprint of Ralstonia solanacearum and its phages

Brown Rot disease of potato is an important plant disease. It leads to significant decreases in potato yield in Egypt and other parts of the world. Therefore, the focus of this work aimed an analysis of the causal agent of this disease [Ralstonia solanacearum] and its phages [from the rhizosphere of potato plants in Egypt] that infect an avirulent strain of this bacterium. The approach taken was to use random amplified polymorphic DNAs [RAPD] by the polymerase chain reaction [PCR] technology. Five decamer oligonucleotide primers OP-Al3; OP-BO2, OP-Bo3, OP-Bo8 and OP-B09 were used in this study to differentiate between the two bacterial isolates virulent [WRCI] and avirulent [DRI] isolataes of R. solanacearum and three lytic phages growing on avirulent strains of this pathogen [RSP1, RSP2 and RSP3]. Statistical analysis of RAPD-PCR polymorphisms results revealed a degree of similarity with ratio of 92.7% between these bacterial isolates. In the case of phages, the statistical analysis of RAPD-PCR polymorphisms revealed a degree of similarities with ratio from 85.7% to 94.7. Therefore, the study paid an attention for the use of RAPD-PCR technology as a new molecular tool for identification and classification of the bacteria as well as the phages

Biocontrol of peanut southern blight [sclerotium rolfsii] by bacillus subtilis

The effective strains of Bacillus subtilis for antagonism against Sclerotium rolfsii in dual cultures were selected. The effects of substrates and cultural conditions on the antagonism of B. subtilis were also studied. S. rolfsii Sacc. caused southern blight disease of a wide range of hosts including leguminosae. The tested peanut plants showed different pre-emergence and post-emergence infection responses towards the four tested S. rolfsii isolates. S. rolfsii isolate number 1 was the most virulent one. Sixteen out of 30 isolates of Bacillus species showed antagonistic activity against S. rolfsii isolate number 1. Richard's medium gave the maximum antagonistic activity. The optimum environmental conditions needed for B. subtilis to give maximum antagonistic activity were 72 hr incubation period, 35C incubation temperature and pH 6. Sucrose and potassium nitrate proved to be the best carbon and nitrogen sources, respectively. MnSO4 [0.01 g/l] was needed to give the maximum antagonistic activity

Application of Trichoderma hamatum as a biocontroller against tomato wilt disease caused by Fusarium oxysparum F. lycopersici

The local isolate of Trichoderma hamatum had an antagonistic potential against Fusarium oxysporum f. lycopersici, the cause of tomato wilt disease. A maximum antagonism was obtained on Richard's medium at 30C and pH 6.0 in the presence of sucrose and ammonium nitrate as carbon and nitrogen sources, respectively. Scanning electron microscopy revealed that the mycoparasite [biocide, T. hamatum] grew directly towards the hyphae of the phytopathogen, followed by the formation of a contact between their hyphae, followed by the disintegration of F. oxysporum f. Lycopersici hyphae in the region of contact. T. hamatum had an extracellular chitinolytic activity in the presence of the phytopathogen as evaluated by agar plate assay. The fungicide Bavistin, the herbicide Ronstar and the insecticide malathion had an inhibitory influence on the radial growth of the phytopathogen and the antagonistic potential of T. Hamatum against the phytopathogen

Nutritional requirements for gelatinase biosynthesis by Streptomyces spheroides

effect of some nutritional factors on gelatinase biosyn-thesis by Streptomyces spheroides was studied. The experimental organism was cultivated at static conditions at 30° and pH 7.0 for 8 days. Starch-nitrate medium was used throughout this work. 0.3% gelatin gave the maximum gelatinase activity among the tested organic and inorganic nitrogen sourced, whereas 2.5% glucose and potassium dibasic phosphate [0.15%] were the most suitable carbon and phosphorus sources, respectively; for gelatinase biosynthesis. The effect of different calcium carbonate concentrations was also tested, 0.1% was the best concentration for gelatinase biosynthesis by Streptomyces spheroides

Aflatoxins production by Aspergillus flavus on whey

Karesh cheese whey was used to investigate its suitability for aflatoxins production by local Aspergillus flavus isolate. The maximum amounts of mycelial dry weights of A. flavus and aflatoxins were produced on sodium chloride free whey [control] and whey plus sodium chloride after incubation for 6 and 9 days, respectively. Clear increases in the amounts of the mycelia of Aspergillus flavus were obtained on whey containing sodium chloride after all incubation periods, while aflatoxins amounts decreased after 3, 6 and 15 days. The lowest and highest amounts of aflatoxins were produced on galaclose and glucose after 3 and 12 days, respectively. In general, all tested carbon sources induced notable decreases in the mycelial dry weights of A. flavus after 3-9 days, compared with the respective values obtained on whey plus sodium chloride, while clear increases in the values of dry weights of A. flavus on all tested carbon sources, except glucose plus mannose, after incubation for 12 and 15 days

Influence of sodium bisulfite as an antimicrobial additive compound on growth and nitrogen metabolism of Aspergillus flavus link

The effect of sodium bisulfite on growth and nitrogen metabolism of Aspergilus flavus link was investigated. The concentrations of 0.015, 0.030 and 0.045% were found to inhibit growth of the fungus by 22.1, 51 .3 and 73.4%, respectively. Toal nitrogen was inhibited by 33.1, 43.2 and 75.5% respectively. Protein was also decreased, the percentage of decrease was a factor of sodium bisulfite concentration. Nucleic acids [RNA and DNA] and its related enzymes [nuclease and ribonuclease T1] were inhibited at all experimental sodium bisulfite concentrations, except ribonuclease T1 which showed a significant increase at 0.015%. Total free amino acids were increased at all sodium bisulfite concenrations. The percentage of increases were 285. 7, 359.8 and 94.4% at 0.015,0.03 and 0.045% sodium bisulfite, respectively Methionine appeared at 0.03%, while praline, valine, isoleucine, leucine, tyrosine and phenyl alanine disappeared at 0.045%

Effect of different concentrations of sodium chloride on the growth and the biochemical activities of aspergillus flavus link

The effect of different sodium chloride concentrations on the growth and aflatoxin B 1 production, as well as protein, total nitrogen, nucleic acids, free amino acids and elemental composition of Aspergillus flavus link isolate was studied. The following is a brief summary of the results: Aflatoxin B 1, protein and nucleic acids production decreased with increasing sodium chloride medium concentration. The free amino acids proline, valine, phenylalanine and arginine showed a notable increase at the concentration of 5% compared with control values, while the amounts of all detectable amino acids at 25% showed very marked increases compared with the values of control or 5%. Methionine, histidine and lycine appeared only at 25%. Sodium chloride induced proline synthesis, its amount increased as sodium chloride increased until it reached maximum at 20%. The amount of total nitrogen showed remarkable decrease at 5%, it reached 19. 05% less than its respective control value, while its value very markedly increased at 25% and reached 43. 68% more than its control value. Also, the amount of total amino acids decreased at 5%, it reached 10. 75% less than its control value, while its value showed remarkable increase at 25% and reached 1270.05% more than its control value. Sodium ion concentration increased at all sodium chloride concentrations, while potassium, iron and magnesium concentration decreased at all sodium chloride concentrations