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In earlier investigations, it has been demonstrated that Pseudocercosporella herpotrichoides (Fron) Deighton is capable of producing pectolytic and cellulolytic enzymes as well as hemicellulases in vitro. The investigation of enzyme activity in extracts from wheat plants infected with P. herpotrichoides (isolates 21e and R6) and from non-infected plants revealed the activity of the following enzymes: pectin methylesterase (PME), polymethylgalacturonase (PMG), pectin lyase (PL), carboxymethylcellulase (CMCase), xylanase and arabanase. Compared to non-infected plants, the enzyme activity in infected plants was considerably higher; in some experiments, only traces of enzyme activity could be found in control plants. The difference in the enzyme activity in infected as compared to non-infected plants was, in most cases, statistically significant, especially beginning at the end of the second week after inoculation. The enzyme activity depended on the temperature during plant cultivation; with the exception of pectin methylesterase (PME), the activity of all investigated enzymes increased with temperature and the highest activity was found in plants grown at 20°C. The highest PME activity was measured in plants grown at 10°C; the activity of this enzyme was generally lower at 15 and 20°C.

Antagonistic activity of 69 Myrothecium isolates belonging to M. carmichaelu, M. cinctum, M. roridum, M. tongaense and M. verrucaria against six soil-borne plant pathogenic fungi was investigated by using the streak method. Results clearly showed that M. carmichaelu is a strong antibiont having a very high degree of antifungal efficacy. M. cinctum and M. tongaense isolates were found to have an antagonistic activity either through antibiosis or mycoparasitism or both against the test fungi. M. roridum and M. verrucaria isolates also possessed both kinds of activities. After this first screening (of all Myrothecium isolates), one isolate from each species exhibiting the highest degree of antagonistic activity was selected for further studies. Inhibitory effects of culture filtrates of these representative isolates on the mycelial growth of the test fungi were investigated by incorporating them into PDA at a dilution of 1:8. M. carmichaelu was the most and M. cinctum the least effective species under assay. Moreover, culture filtrates and mycelium extracts of the selected isolates were found to have both antifungal and antibacterial properties using the agar-well method. Among the test fungi, Sclerotinia sclerotiorum proved to be generally the most, and Pythium debaryanum the least sensitive to the antibiotic effects. M. cinctum showed the widest antibacterial spectrum inhibiting five bacterial species except for Pseudomonas syringae Pv. Phaseolicola. Additionally, the observations using light and scanning electron microscopy clearly demonstrated that all of the five Myrothecium species were able to parasitize all of the tested fungi.

Ultrastructural observations showed massive accumulation of electron dense deposits adjacent to plasmalemma and mitochondria and mitochondrial degeneration, which probably leads to cell death, in some hyphae and haustoria of Phytophthora infestans in infected tomato leaves treated with the systemic fungicide oxadixyl (8 μg/ml). However, no changes in the endoplasmic reticulum and number of ribosomes were observed. The cell walls of some hyphae were markedly thickened after oxadixyl treatment. Degenerated haustoria were partly present in intact host cells. Evidently, fungal cell damage by treatment with oxadixyl is not correlated with host cell damage.

In field experiments, winter wheat was grown under different crop rotation regimes (monoculture; rotation with field beans) and differentiated intensity (cv.‘Jubilar’ with 120 kg N/ha and 1l CCC/ha; cv.‘Okapi’ with 180 kg N/ha and l CCC/ha). Plant, protection measures were carried out at three levels (no treatment; specific treatments under consideration of damage thresholds; routine spraying program). The occurrence of aerobic bacteria, fluorescent pseudomonads and strong siderophore-producers as well as the effect of the different cropping systems on the two groups of bacteria mentioned last were determined during the vegetation period at the beginning of shooting, at full bloom and after harvesting on the surface of the roots of wheat plants. In comparison to the total population of aerobic bacteria, the populations of fluorescent pseudomonads and of the strong siderophore-producing bacteria changed in a characteristic way: whereas at the beginning of shooting the highest and at full bloom the, lowest numbers were determined, a slight increase could be observed after harvest. On roots of wheat plants in monoculture, higher numbers of fluorescent pseudomonads and strong siderophore-producers were detected at the begining of shooting and at full bloom, than on those grown in rotation with field beans. The roots of cv. ‘Okapi’ (higher cropping intensity) were colonized to a higher degree by both groups of bacteria as compared to those of cv. ‘Jubilar’. After application of herbicides, a stimulation of these micro-organisms was observed at the beginning of shooting. The influences of different crop rotation schemes, intensities of cropping and plant protection measures on the occurrence of fluorescent pseudomonads were altogether less pronounced than the natural fluctuations of the population during the growth of the wheat. On the basis of morphological, physiological and biochemical properties, it could be shown that different biovars of the species Pseudomonas fluorescens dominated in the experimental field.

An isolate of Neocosmospora vasinfecta var. africana (F-2) was assayed for its antagonistic activity against 15 soil-borne fungi; 14 of them were important plant pathogens. The fungus exhibited a strong antibiotic effect against most of the fungi under test. While Pythium debaryanum, Macrophomina phaseolina, Phytophthora capsici, Sclerotinia sclerotiorum, Cochliobolus sativus and Alternaria alternata showed a very high degree of sensitivity as evidenced by the respectivezones of inhibition caused by the antagonist, Phoma betae, Rhizoctonia solani and Verticillium dahliae proved to be the most resistant. A mutual antibiosis existed between N. vasinfecta var. africana and five of the test fungi. The culture filtrate of the antagonist, diluted ten times with PDA, suppressed the mycelial growth of P. debaryanum and P. capsici completely. Whereas in this test R. solani proved to be the least sensitive, the remaining test fungi showed some differences in their susceptibility, but in any case their growth was inhibited significantly as compared to the controls.

By means of a modified agar-ring method, the antibiotic efficacy of 300 isolates of actinomycetes, obtained from soil samples from Turkey, against six different test fungi was investigated. A wide range in their degree of sensitivity was evident. Whereas Sclerotinia sclerotiorum was completely inhibited by more than 90 % of the tested isolates, Rhizoctonia solani and Alternaria alternata were suppressed by only 17 and 14 %, respectively; Pythium debaryanum, Cochliobulus sativ, us and Macrophomina phaseolina held an intermediate position. Isolates which completely prevented the growth of Rhizoctonia solani and Alternaria alternata, were usually also highly effective against the other test fungi. Possible conclusions which may be drawn from these results are discussed.

In studies conducted to gain information on the antagonistic potential of Acrophialophora levis, an isolate obtained from the rhizosphere of olive trees in Aegean Region (Turkey) was assayed in vitro for its antibiotic activity against 16 important soil-borne plant pathogenic fungi belonging to Mastigomycotina, Ascomycotina, Basidiomycotina and Deuteromycotina, and six bacteria by using the streak method. The results of this study clearly demonstrated that A levis exhibited an antagonistic activity against all of the test fungi and three of the test bacteria through antibiosis. As evidenced by the respective zones of inhibition, Botrytis cinerea and Sclerotinia sclerotiorum proved to be extremely susceptible; Pythium debaryanum, Rhizoctonia solani and Phytophthora capsici appeared to be the most resistant among the fungi tested. Among the test bacteria, Cory neb acterium michiganense pv. michiganense, Bacillus subtilis and Xanthomonas campestris pv. vesicatoria showed some sensitivity to the antibiotic effect of this antagonist. Zusammenfassung Antagonistische Wirksamkeit von Acrophialophora levis Samson and Tariq Mahmood In Untersuchungen, die Aufschlus uber das antagonistische Potential von Acrophialophora levis in vitro geben sollten, wurde ein Isolat, das aus der Rhizosphare von Olivenbaumen in der agaischen Region (Turkei) gewonnen worden war, auf seine antibiotische Wirkung gegenuber 16 bodenburtigen phytopathogenen Pilzen aus den Gruppen der Mastigomycotina, Ascomycotina, Basidiomycotina und Deuterornycotina sowie gegenuber sechs Bakterien-Arten gepruft. Dabei konnte nachgewiesen werden, das A. levis eine antagonistische Wirkung auf aile Testpilze und auf drei der Testbakterien ausubt, Gemessen an der Breite der Hemmzonen, erwiesen sich Botrytis cinerea und Sclerotinia sclerotiorum als besonders empfindlich; dagegen waren Pythium debaryanum, Rhizoctonia solani und Phytophthora capsici die widerstandsfahigsten unter den gepruften Pilzen. Von den Testbakterien liesen Corynebacterium michiganense pv. michiganense, Bacillus subtilis und Xanthomonas campestris pv. vesicatoria eine gewisse Sensitivitat gegenuber der antibiotischen Wirkung des Antagonisten erkennen.

Investigations on the production of extracellular hemicellulases by Pseudocercosporella herpotrichoides in vitro For all 15 isolates of Pseudocercosporella herpotrichoides investigated, xylanase as well as arabanase activity could be demonstrated. After cultivation of 3 weeks, the activity of the enzymes reached a peak. The activity of xylanase was considerably increased by addition of xylan in comparison to Maltzin as the sole source of carbohydrate. Also the arabanase activity could be increased significantly by addition of araban or xylan as compared to the Maltzin variant. The optimum temperature with regard to activity and stability of xylanase ranged at 50°C. The pH-optimum for xylanase activity was found to be at pH 5.0, and the enzyme was stable in ° range between pH4.0 and 8.0 (9.0). In case of arabanase, the temperature optimum varied between 40 and 50°C; up to this temperature, the enzyme was also stable. At pH 5.0, the arabanase activity reached its optimum; stability was observed in - pH range between 4.0 and 9.0. In extracts prepared from autoclaved wheat coleoptiles which were inoculated with Pseudocercosporella herpotrichoides, the presence of the enzymes xylanase, arabanase, cellulase and polymethylgalacturonase could be demonstrated. The enzyme activities of the inoculated samples were considerably higher than those of non-inoculated controls. The differences, in most cases, were statistically significant. Der Deutschen Forchungsgemeinschaft danken wir fur finanzielle Unterstutzung.

Incidence of yellow leaf blotch (Drechslera tritici-repentis) on winter wheat in dependence on crop rotation and under the influence of different spray programs On winter wheat grown on two experimental fields in different crop rotation programs, a severe incidence of Drechslera tritici-repentis on the leaves was observed. Monoculture of wheat resulted in a significantly higher attack than growing in rotation with other crops. A distinct relation between different spray programs and disease severity could be found only in isolated cases.