v | ok | Kirjasto Aj-K | Maan pieneliöstön merkityksestä apilan Sclerotinia Trifoliorum erikss. infektiota rajoittavana tekijänä vuoden eri aikoina

In the petri dish trials the mycelia of Sclerotinia trifoliorum in sterilized soil samples generally infected clover quite readily. In unsterilized samples the infection was less severe and showed marked variations in different years and at different times of the year. In the outdoor trials clover became less infected in the middle of the summer than in the spring and autumn. On the other hand, in the thermostat trials, where the temperature was constantly 7—10°C, the temperature at the time of taking the soil samples did not have a pronounced effect on the extent of clover infection. Liming of the soil caused a marked decrease in the severity of clover rot infection. In some autumns clover plants growing in soil samples taken from fallow were more seriously infected than those growing in soil from a clover field. As a rule, however, there were only slight variations in the extent of infection in the soil samples taken at the same time from the various areas of the field cultivated in different ways. In general, the highest numbers of microorganisms in the soil were found in the autumn and the lowest in the spring. In clover fields there were often more microorganisms – particularly in the autumn – than in fallow. Liming caused an increase in the numbers of soil microbes. S. trifoliorum infected clover very severely at temperatures of 0—5°C; in the range 5—21°C the infection grew generally milder the more the temperature was found to be rising. At temperatures of 5– 10°C an increase in the numbers of soil microbes resulted in a decrease in the infection of the clover. Still higher temperatures, which did not increase the numbers of soil microorganisms, nevertheless enhanced the antagonistic power of the soil.

The positional and fatty acid specificities of lipases from several different microorganisms have been examined by gas–liquid chromatographic analysis of the free fatty acids following action on mixed triglycerides of known composition. Three types of lipases were found. Lipases of the first type, obtained from several microorganisms, attacked primarily the 1-position of the triglyceride in a manner similar to that of pancreatic lipase. Some fatty acid preference was also observed. The ability of the lipolytic enzymes from Staphylococcus aureus and Aspergillus flavus to attack the 2-position as well as the 1-position suggested another type of activity. The lack of any appreciable effect of diisopropylfluorophosphate in 10−4m concentrations on this hydrolysis indicated it was not an esterase. The third type of lipase was from Geotrichum candidum and it preferentially hydrolyzed the oleate ester from the triglyceride regardless of its position. Possible applications of these lipases are discussed.

In the petri dish trials the mycelia of Sclerotinia trifoliorum in sterilized soil samples generally infected clover quite readily. In unsterilized samples the infection was less severe and showed marked variations in different years and at different times of the year. In the outdoor trials clover became less infected in the middle of the summer than in the spring and autumn. On the other hand, in the thermostat trials, where the temperature was constantly 7—10°C, the temperature at the time of taking the soil samples did not have a pronounced effect on the extent of clover infection. Liming of the soil caused a marked decrease in the severity of clover rot infection. In some autumns clover plants growing in soil samples taken from fallow were more seriously infected than those growing in soil from a clover field. As a rule, however, there were only slight variations in the extent of infection in the soil samples taken at the same time from the various areas of the field cultivated in different ways. In general, the highest numbers of microorganisms in the soil were found in the autumn and the lowest in the spring. In clover fields there were often more microorganisms – particularly in the autumn – than in fallow. Liming caused an increase in the numbers of soil microbes. S. trifoliorum infected clover very severely at temperatures of 0—5°C; in the range 5—21°C the infection grew generally milder the more the temperature was found to be rising. At temperatures of 5– 10°C an increase in the numbers of soil microbes resulted in a decrease in the infection of the clover. Still higher temperatures, which did not increase the numbers of soil microorganisms, nevertheless enhanced the antagonistic power of the soil. | Petrinmaljakokeissa Sclerotinia trifoliorumin rihmasto saastutti steriloiduissa maanäytteissä apilaa yleensä verraten hyvin. Steriloimattomissa maanäytteissä sen saastutuskyky oli pienempi ja eri vuosina sekä eri vuodenaikoina varsin vaihteleva. Ulkona suoritetuissa kokeissa apila saastui lievemmin keskikesällä kuin keväällä ja syksyllä. Sen sijaan termostaattikokeissa, joissa lämpötila oli jatkuvasti 7–10°C, ei maanäytteen ottamisajankohdanlämpötilalla ollut selvää vaikutusta apilan saastumiseen. Kalkitus heikensi apilamätäsienen saastutuskykyä huomattavasti. Eräinä syksyinä apilamätäsieni saastutti ankarammin kesannosta kuin apilapellosta otetussa mullassa kasvanutta apilaa. Yleensä ei apilamätäsienen saastutuskyky kuitenkaan kovin paljon vaihdellut saman peltolohkon eri tavoin viljellyistä osista keskenään samaan aikaan otetuissa maanäytteissä. Mikrobeja oli maassa yleensä eniten syksyllä ja vähiten keväällä. Apilapellossa oli mikrobeja usein, etenkin syksyisin, enemmän kuin kesantomaassa. Kalkitus lisäsi mikrobien määrää. S. trifoliorum saastutti apilaa hyvin ankarasti 0—5 °C:n lämpötiloissa ja 5—21°C:n lämpötiloissa yleensä sitä lievemmin mitä korkeampi lämpötila oli. 5—10°C:n lämpötiloissa apilan saastuminen heikkeni maan mikrobiluvun noustessa. Korkeammat lämpötilat, jotka eivät suurentaneet mikrobien lukua maassa, lisäsivät kuitenkin maan antagonistista voimaa.

A method has been described for the isolation of protamine from the milt (testes) of fish, employing direct extraction of the organ with dilute sulfuric acid, followed by stepwise precipitation with ethanol. The growth inhibitory effect of different protamine preparations on Saccharomyces carlsbergensis have been studied. 0, 7-0,8 µg clupeine sulphate per ml medium gave complete growth inhibition. It has been pointed out that the type (origin) of the protamine should be given in studies on these substances. The growth inhibition of clupein sulphate on some microorganisms employed in vitamin assays have been tried. For L. plantarum and L. leichmannii growth inhibition was observed at about 5 µg per ml medium, for L. casei at 10 µg, for S. fæcalis at about 150 µg, and for Neurospora crassa at about 50 µg per ml medium Aspergillus niger showed growth promotion, probably caused by enzymatic breakdown of the polypeptide and utilization of the free amino acids.

Microbial mechanisms of soil aggregate stabilization were investigated as a function of microbiological and water-stability changes of incubated artificial aggregates, 2 to 4.76 mm. in size composed of soil particles < 0.5 mm., prepared from Waupun silt loam. Aggregate water-stability was determined by wet-sieving and expressed as the percentage of soil material bound into water-stable aggregates 0.5 to 1 mm., 1 to 2 mm. and > 2 mm. in size. Microbial development was investigated by dilution plate and microscopic methods. Aggregate stabilization was a function more of microbial synthesis of soil-binding substances than of numbers of microorganisms. Extensive production of mycelium and spores in soil aggregates by a fungus known to be capable of aggregate stabilization, did not, necessarily, result in an increase in the stability of the aggregates. Stabilization of aggregates by Mucor silvaticus involved the binding of soil particles into > 2 mm. water-stable aggregates at all stages of incubation. Aggregates stabilized under anaerobic conditions exhibited a high percentage contribution of 0.5- to 1-mm. and 1- to 2-mm. aggregates to total stability in the early stages of incubation. A relatively high proportion of the total water-stability of sucrose-amended aggregates possessing the indigenous mixed microflora was attributable to stable 0.5- to 2-mm. aggregates in the early stages of aerobic incubation, an indication that bacteria were more important than fungi in the initial stabilization of these aggregates.