A bioassay for predicting the resistance of wheat leaves to Septoria nodorum

Plants of the winter wheat cv. Bounty were inoculated with Septoria nodorum and then assayed for ergosterol. A detached leaf technique was used in which leaf segments were incubated on agar containing benzimidazole. Four levels of a conidial suspension inoculum were applied using a measured droplet technique. Ergosterol in plant extracts was measured using HPLC and its identity confirmed by co-injection with pure ergosterol as an internal standard. The extracts were also assayed by silica-gel thin layer chromatography with the sterol being visualised with rhodamine; the presence of ergosterol in the material from the two higher disease level treatments was confirmed by analysing the eluted spots in a spectrophotometer. Additional confirmation of ergosterol was obtained using gas-liquid chromatography comparing a mixture of known plant sterols with a sample from the diseased leaf tissue. The ergosterol assay was found to be very sensitive and offers a high level of reproducibility. It would therefore appear that such assays could be of value in breeding programmes when it is necessary to screen wheat cultivars for their reaction to S. nodorum or other fungal pathogens.     

Studies on Acid Tolerance of Rhizobium trifolii in Culture and Soil

Several experiments were carried out in an attempt to isolate and adapt strains of Rhizobium trifolii to growth at low pH on citrate-phosphate buffered yeast-extract mannitol agar (CPYEM). In another experiment, two streptomycin resistant strains (7A str^r and 16 str^r ) with contrasting tolerances to acidity in culture were evaluated for survival in acid upland soils.
No acid tolerant clones were isolated from three strains on CPYEM suggesting that there were no cells with greater tolerance of low pH present. The stepwise subculture of several strains on media of decreasing pH also failed to increase their acid tolerance. Growth initiation on CPYEM at pH 4–4 was a function of the number of viable cells in the inoculum and was accompanied by a rise in pH.
In three acid soils, strain 7A str^r was more persistant than 16 str^r , whereas in culture the converse was true. Survival of these strains in the acid soils was inversely related to acid production on the medium of Norris (1965) in agreement with Norris's hypothesis. Ameliorating soil pH with lime improved the persistency of both strains. Prior exposure of 7A str^r and 16 str^r to the acid soils failed to improve subsequent survival in these soils.     

C-4 Pathway in <Emphasis Type="Italic">Pennisetum purpureum</Emphasis>

HIGH rates of photosynthesis and low rates of photorespiration are found in several plant species in which the photosynthetic carbon reduction (PCR) cycle is augmented by a second carboxylation system, the C-4 pathway^1,2. This pathway does not result in a net fixation or reduction of carbon, but seems to operate as a mechanism for concentrating CO₂ at the site of reductive assimilation. It has been widely accepted that the carboxylation reaction of the C-4 pathway is associated with the chloroplasts of mesophyll -cells, while PCR cycle activity is restricted to the bundle sheath chloroplasts. Investigations^3–5 indicate, however that mesophyll chloroplasts do contain PCR cycle activity, arni that the C-4 pathway is located in the cytoplasm of non-green and mesophyll cells.     

Components of partial resistance to Septoria nodorum in winter wheat

Components of partial resistance to Septoria nodorum were investigated in 10 cultivars of winter wheat having similar field resistances. The components measured were infection frequency, latent period, size, shape and rate of growth of lesions, spore production and its rate of increase. Latent period was found to be lognormally distributed. Some of the components of resistance were found to be significantly different between cultivars. Cluster analysis also showed that cultivars could be distinguished on the basis of their components of resistance. Principal components analysis indicated that resistance could be broken down into four underlying factors, three of which could be readily interpreted. The measurements of the components of resistance were combined in a model, the r-index, based on Van der Plank's r. The amount of variation between cultivars cast some doubt on the predictive value of the index but all the cultivar values were well within the range bounded by two ‘synthetic’ cultivars made up of combinations of either the most resistant or the most susceptible components. It is considered that the r-index has potential in screening for field resistance. The possibility of incorporating the most resistant-type components into one cultivar is discussed. The use of cultivar mixtures containing cultivars having similar field resistances is also discussed in the light of the variability found in this study.     

Immunoglobulin Determinants on Lymphocytes of Adult,Neonatal and Foetal Pigs

THE initiation of antibody response is thought to depend on the binding of antigen to receptors on the membrane of lymphoid cells. There is evidence that receptors are antibody-like and composed of immunoglobulin light and heavy chains, which can be demonstrated using reactions with antiglobulin sera.