Direct effect of biocontrol agents on wilt and root-rot diseases of sesame

In Egypt, sesame cultivation is subject to attack by wilt and root-rot diseases caused by Fusarium oxysporum f.sp. sesami (Zap) Cast. and Macrophomina phaseolina (Maubl) Ashby causing losses in quality and quantity of sesame seed yield. Bacillus subtilis and Trichoderma viride isolates which were isolated from sesame rhizosphere were the most effective to antagonise fungal pathogens, causing high reduction of hyphal fungal growth. Trichoderma viride was found to be mycoparasitic on Fusarium oxysporum f.sp. sesami and M. phaseolina causing morphological atternation of fungal cells and sclerotial formation. In general, Bacillus subtilis, T. viride, avirulent Fusarium oxysporum isolate and Glomus spp. (Amycorrhizae) significantly reduced wilt and root-rot incidence of sesame plants at artificially infested potted soil by each one or two pathogens. Data obtained indicate that Glomus spp significantly reduced wilt and disease severity development on sesame plants followed by T. viride. Meanwhile, avirulent Fusarium oxysporum isolate followed by Glomus spp. were effective against root-rot disease incidence caused by M. phaseolina. Glomus spp. followed by B. subtilis significantly reduced wilt and root-rot disease of sesame plants. All biotic agents significantly reduced F. oxysporum f.sp. sesami and M. phaseolina counts in sesame rhizosphere at the lowest level. Glomus spp. and the avirulent isolate of F. oxysporum eliminated M. phaseolina in sesame rhizosphere. Meanwhile T. viride was the best agent at reducing F. oxysporum at a lower level than other treatments. Application of VA mycorrhizae (Glomus spp.) in fields naturally infested by pathogens significantly reduced wilt and root-rot incidence and it significantly colonised sesame root systems and rhizospheres compared to untreated sesame transplantings.     

Changes in sensitivity of Amaranthus retrof/exus L. seeds to ethylene during preincubation. I. Constant temperatures

Abstract. Germination responses of redroot pigweed ( Amaranthus retroflexus L.) seeds to ethylene were determined at 25, 30, 35, or 40° C after preincubation at various temperatures (15–35° C) for different periods (0.5–32 d). After 7 d preincubation, seeds showed a log-linear germination response to ethylene concentration in most of the temperature treatments. Sensitivity to ethylene increased with longer preincubation; response thresholds of 0.03−0.09 cm³ m⁻³ were observed after 32 d, compared to 0.18−1.6 cm³ m⁻³ after 7 d of preincubation. Preincubation at 15 or 20° C generally enhanced germinability, whereas 25 or 30° C produced secondary dormancy, which was readily broken with ethylene. Temperature during preincubation also significantly influenced the slope of the dose-response curve. The responses of preincubated redroot pigweed seeds to ethylene suggested that, in the field, seeds would probably not lose their sensitivity to this gas during prolonged burial in soil.     

Disease development of Pythium root rot in bulbous Iris and Crocus

Iris bulbs and Crocus corms were planted at two planting dates in sandy soil infested with Pythium spp. At monthly intervals during the growing season root rot infection was assessed over 3 consecutive years and disease development curves were predicted for both crops. The disease development was remarkably different for Iris and Crocus and the curve shape was determined by the crop rather than by the Pythium species. Planting date had a significant effect on disease development in both crops. No correlation was found between disease development and soil temperature.     

The First Record and Characterization of Powdery Mildew (Erysiphe pachypodiae sp. nov.) on Pachypodium lamerei (Apocynaceae)

During the summer and autumn of 1999, symptoms of powdery mildew disease were first observed on Pachypodium lamerei in the Czech Republic. White lesions of irregular shape appeared on leaf margins and spread towards the central vein of the leaf, often followed by necrosis of leaf tissue. In the spring of 2000, the sexual stage (cleistothecia) also appeared on infected leaves. Based on the observations of the morphology of its anamorph and teleomorph stage as well as on results from inoculation experiments, the identity and origin of this powdery mildew species are discussed. Based on the pseudoidium anamorph, this fungus may be clearly assigned to Erysiphe emendation, probably to section Uncinula, since the cleistothecial appendages are non‐mycelioid and occassionally circinate at the apex. The fungus is described as a new species Erysiphe pachypodiae sp. nov.     

Ethanol-induced death in yeast exhibits features of apoptosis mediated by mitochondrial fission pathway

Cell death in yeast (Saccharomyces cerevisiae) involves several apoptotic processes. Here, we report the first evidence of the following processes, which are also characteristic of apoptosis, in ethanol-induced cell death in yeast: chromatin condensation and fragmentation, DNA cleavage, and a requirement for de novo protein synthesis. Mitochondrial fission protein, Fis1, appears to mediate ethanol-induced apoptosis and ethanol-induced mitochondrial fragmentation. However, mitochondrial fragmentation in response to elevated ethanol levels was not correlated with cell death. Further, in the presence of ethanol, generation of reactive oxygen species was elevated in mutant fis1Delta cells. Our characterization of ethanol-induced cell death in yeast as being Fis1-mediated apoptosis is likely to pave the way to overcoming limitations in large-scale fermentation processes, such as those employed in the production of alcoholic beverages and ethanol-based biofuels.