The effect of introducing the aphid-pathogenic fungus Erynia neoaphidis into populations of cereal aphids

The aphid-pathogenic fungus Erynia neoaphidis, as dried fungus-infected aphids, was applied to caged plots of winter wheat infested with cereal aphids at two sites, one in Hertfordshire and the other in Hampshire, in 1983. In each trial, the fungus became established in the aphid populations in the treated plots even though conditions were drier than average and therefore sub-optimal for fungus spread. Treatment applied in the third week of June increased the proportion of infected aphids more than that applied two weeks later at one site, and the early application was the only treatment to have an obvious effect at the other. In spite of the observed effect of treatments on the proportion of infected aphids, the fungus failed to reduce the numbers of aphids relative to those in untreated plots, chiefly because in these plots many aphids were killed by fungi of the same species as that introduced and other related species from natural sources. Artificial introduction of E. neoaphidis acts too slowly and unpredictably to be likely to form a practical alternative to conventional insecticides for cereal aphid control.     

Stomatal Responses to Applied ABA and CO2 in Epidermis Detached from Well-Watered and Water-Stressed Plants of Commelina communis L.

Epidermal strips from either well-watered or water-stressedplants of Commelina communis L. were subjected to a range ofABA concentrations (10^–6–10^–3 mol m^–3)in the presence (330 parts 10^–6 in air) or virtual absence(3 parts 10–6 in air) of CO₂. The stomatal response toCO₂ was greater in epidermis from water-stressed plants, althoughthere was a distinct CO₂ response in epidermis from well-wateredplants. Additions of ABA via the incubation medium had littleeffect on the relative CO₂ response. Stomata responded to ABAboth in the presence and virtual absence of CO₂, but the relativeresponse to ABA was greatest in the high CO₂ treatment. Whenwell-watered plants were sprayed with a 10^–1 mol m^–3ABA solution 1 d prior to use, the stomatal response of detachedepidermis to both CO₂ and ABA was very similar to that of epidermisdetached from water-stressed leaves. It is hypothesized thata prolonged exposure to ABA is necessary before there is anymodification of the CO₂ response of stomata.     

Ultrastructural and Cytochemical Studies of 'Air Blisters' in Pilea cadierei Gagnep. and Guillaumin

Cells from the sub-epidermal layer of Pilea cadierei preparedfor electron microscopy using standard fixation and embeddingprocedures appear extremely osmiophilic, with the organellesstanding out in negative relief. However, when tissues werefixed in glutaraldehyde supplemented with either procaine orcaffeine (substances known to complex with phenols) the osmiophilicmaterial was generally limited to the vacuole. After procaineor caffeine fixation the surrounding cytoplasm appeared as inadjacent, nonphenolic cells. Some small aggregates of phenolicmaterial appear in the cisternae of the endoplasmic reticular,indicating these organelles may be involved in either the synthesisor transport of phenolics in Pilea. Since one of the major functionsof phenolics is in light-screening, air blisters may serve toscreen out damaging radiation from the underlying tissue. Thepresence of typical shade-type plastids in Pilea air blistersis a further indication of this light-screening role. Pilea cadierei, aluminium plant, air blister, cytochemistry, ultrastructure, light screening, phenolics     

Identification of immature aphids by chromatography

• 1 Immature apterae of five species of cereal aphid were distinguished by ultraviolet examination of chromatograms of their fluorescent pigments.
• 2 Non-expert examiners could identify Metopolophium dirhodum, Sitobion fragariae and Rhopalosiphumpadi with a mean reliability of 98, 83 and 71% respectively; Metopolophium festucae and Sitobion avenae could be separated from the rest but not from each other.
• 3 All species gave consistent chromatograms whether reared on oats or on wheat: some species produced atypical traces if reared on certain grasses.

     

Effects of carbon dioxide concentration on the interactive effects of temperature and water vapour on stomatal conductance in soybean

Soybeans were grown at three CO₂ concentrations in outdoor growth chambers and at two concentrations in controlled-environment growth chambers to investigate the interactive effects of CO₂, temperature and leaf-to-air vapour pressure difference (LAVPD) on stomatal conductance. The decline in stomatal conductance with CO₂ was a function of both leaf temperature and LAVPD. In the field measurements, stomatal conductance was more sensitive to LAVPD at low CO₂ at 30 °C but not at 35 °C. There was also a direct increase in conductance with temperature, which was greater at the two elevated carbon dioxide concentrations. Environmental growth chamber results showed that the relative stomatal sensitivity to LAVPD decreased with both leaf temperature and CO₂. Measurements in the environmental growth chamber were also performed at the opposing CO₂, and these experiments indicate that the stomatal sensitivity to LAVPD was determined more by growth CO₂ than by measurement CO₂. Two models that describe stomatal responses to LAVPD were compared with the outdoor data to evaluate whether these models described adequately the interactive effects of CO₂, LAVPD and temperature.     

The effect of pH on host plant 'preference' for strains of Rhizobium trifolii using fluorescent ELIS A for strain identification

The effect of pH on host plant ‘preference’ for strains of R. trifolii was studied using the fluorescent ELISA technique. Four white clover cultivars were compared growing at pH 5, 6 and 7 inoculated with 1:1 mixtures of two strains of R. trifolii, CP3B and R4. The growth of these two bacterial strains was also studied at the same pH levels in pure culture. At pH 5, in pure culture, CP3B grew very well but R4 failed to reach the log phase. CP3B also produced the majority of nodules at this pH (86%). At pH 7, in pure culture, R4 grew better than CP3B and also produced 66% of the nodules in the nodulation experiment. However, there was good evidence of host cultivar ‘preference’ with cv. Milkanova having no nodules inhabited by CP3B at pH 7 but cv. S100 having 32%. The results are discussed from the point of view of the establishment of white clover in acid soils and the usefulness of the fluorescent ELISA technique for Rhizobium strain identification is also emphasised.     

The Effect of Cotyledon Excision on Reproductive Development in Pea (Pisum sativum L.)

The excision of cotyledons from two cultivars of peas soon aftergermination resulted in a lowering of the node of first floweringas well as a delay in both flower initiation and flowering,especially in the late cultivar Greenfeast. This is contraryto the usual view that, when cotyledon excision reduces nodeof first flowering, flower initiation and flowering are hastened,and it seems irreconcilable with the colysanthin theory of Barber(1959). An alternative explanation is proposed.