Powdery mildew of tabacco (Erysiphe cichoracearum DC.)

The natural spread of Erysiphe cichoracearum was assessed weekly on alternate leaves of irrigated and non-irrigated tobacco plants of Kutsaga 51 variety, grown in field plots in 1962-63. Leaf area, air temperature and humidity within the plots, relative turgidity of the leaves and soil moisture were also measured. Leaves emerged over a period of 37 days. A minimum of 29 days elapsed between leaf emergence and infection; irrigation lengthened this period by 2–6 days for leaves 2–6 and shortened it by 2–10 days for leaves 10–18. The duration of the initial resistant phase, in leaves at comparable stalk positions, appeared to be directly proportional to the eventual size of the leaves at reaping. Leaves were not infected until they were almost fully expanded. The longest dry period, when most irrigation water was applied, occurred when most lower leaves (2–8) were fully expanded and already infected; upper leaves (10–18)w ere then still expanding and not yet infected. Irrigation increased infection in all leaves; it increased the growth of the pathogen during dry weather and the subsequent susceptibility of leaves that were still actively expanding but not yet infected. Irrigation increased the percentage of susceptible leaf area infected, of intact plants, threefold and that of topped plants ninefold. Topped plants had less infection than intact ones.     

Changes in the resistance of tobacco leaf to Erysiphe cichoracearum DC. induced by topping,cytokinins and antibiotics*

Treatments that produced different rates of growth in attached tobacco leaves and leaf discs, also affected the growth of powdery mildew on them. Topping (removal of flower head) increased the resistance of upper leaves, and attached leaves of topped and intact plants were more susceptible than leaf discs from them incubated on water. Hyphal growth increased on leaf discs incubated on water at increasing light intensities, as did dry and fresh mass of healthy discs. On kinetin, dry and fresh mass also increased with light intensity but hyphal growth decreased slightly. Discs incubated at all light intensities on kinetin had less hyphal growth than those on water at the lowest intensity (< 50 lx). Floating leaf discs on chloramphenicol at 500 μ/ml restricted fungal growth but not quite as much as kinetin (10 μ/ml); kinetin inhibited the fungus in the presence of chloramphenicol. Actinomycin D (2.μ5 μ/ml) and puromycin (5.0 μml) had little effect on the fungus.     

Enzyme polymorphisms in the House Sparrow, Passer domesticus

Methods are described for the visualization of 20 enzymes from the house sparrow, Passer domesticus, in starch gels and by iso-electric focussing. Many of the methods are applicable to other avian species. Two samples of sparrows from the east midlands of England have been analysed. The patterns that are manifest in the gels can be ascribed to between 33 and 35 loci, of which the same nine are polymorphic in both samples. The level of heterozygosity in these birds is about 15%, which at first sight is higher than an introduced population in Australia. However, this difference disappears when homologous loci are compared.     

Using a logical model to predict the growth of yeast

Background  

A logical model of the known metabolic processes in S. cerevisiae was constructed from iFF708, an existing Flux Balance Analysis (FBA) model, and augmented with information from the KEGG online pathway database. The use of predicate logic as the knowledge representation for modelling enables an explicit representation of the structure of the metabolic network, and enables logical inference techniques to be used for model identification/improvement.