The effects of post-inoculation wet and dry periods, and inoculum concentration, on lesion numbers of Septoria nodorum in spring wheat seedlings

Lesion numbers in seedlings of spring wheat cvs Kolibri and Maris Butler, inoculated with Septoria nodorum in a growth cabinet, varied with the length of wet or dry period following inoculation. Increasing the length of dry period led to a curvilinear decrease in lesion numbers at 15° C (60% r.h.) and 20° C (40% r.h.), but some infection still occurred with a dry period of 72 h. Increasing the length of wet period gave a linear increase in lesion numbers in cv. Maris Butler, but lesion numbers levelled off at 12 h at 15° C (60% r.h.) in cv. Kolibri. Increasing the inoculum concentration gave an increase in lesion numbers in both cultivars irrespective of whether wet or dry periods followed inoculation. On occasion, Kolibri and Maris Butler differed significantly in lesion numbers, but differences were not consistent between experiments, and there were interactions with the length of wet period.     

Predicted impact of climate change on European bats in relation to their biogeographic patterns

There has been considerable recent interest concerning the impact of climate change on a wide range of taxa. However, little is known about how the biogeographic affinities of taxa may affect their responses to these impacts. Our main aim was to study how predicted climate change will affect the distribution of 28 European bat species grouped by their biogeographic patterns as determined by a spatial Principal Component Analysis. Using presence‐only modelling techniques and climatic data (minimum temperature, average temperature, precipitation, humidity and daily temperature range) for four different climate change scenarios (IPCC scenarios ranging from the most extreme A1FI, A2, B2 to the least severe, B1), we predict the potential geographic distribution of bat species in Europe grouped according to their biogeographic patterns for the years 2020–2030, 2050–2060 and 2090–2100. Biogeographic patterns exert a great influence on a species' response to climate change. Bat species more associated with colder climates, hence northern latitudes, could be more severely affected with some extinctions predicted by the end of the century. The Mediterranean and Temperate groups seem to be more tolerant of temperature increases, however, their projections varied considerably under different climate change scenarios. Scenario A1FI was clearly the most detrimental for European bat diversity, with several extinctions and declines in occupied area predicted for several species. The B scenarios were less damaging and even predicted that some species could increase their geographical ranges. However, all models only took into account climatic envelopes whereas available habitat and species interactions will also probably play an important role in delimiting future distribution patterns. The models may therefore generate ‘best case’ predictions about future changes in the distribution of European bats.     

Growth in vitro and Metabolism of Plasmodium vinckei chabaudi*

SYNOPSIS. An in vitro system, based on the rocker dilution technic, has been developed that supports intraerythrocytic growth of a rat-adapted strain of Plasmodium vinckei chabaudi from ring to schizont stages; some reinvasion was obtained, although invariably, this was associated with a decrease in parasite numbers. Pertinent features were the very high buffer content of the medium and the low oxygen tension of the gaseous phase. Lactate production, glucose utilization, and ³H-leucine and ³H-adenosine incorporations were investigated for their suitability to monitor parasite growth. Throughout an 18-hr incubation there was a continuous and increasing production of lactate and utilization of glucose, which correlated well with the development of the parasites from ring to schizont stages. During the same period, there was a low but continuous and increasing incorporation of ³H-leucine into parasite protein. However, ³H-adenosine was incorporated only for the 1st hr of incubation, after which time no net incorporation occurred. Parasites grew normally from ring to schizont stages even in the absence of adenosine from the dilution medium.     

The competitive ability and symbiotic effectiveness of doubly labelled antibiotic resistant mutants of Rhizobium trifolii

Doubly labelled mutants of Rhizobium trifolii , resistant to streptomycin and spectinomycin, were studied in respect of nodulating competitiveness and symbiotic effectiveness relative to the 'wild-type' parent strains using Trifolium repens cv. S184 as the host plant.
A combination of antibiotic resistance, differential absorption of congo-red and the fluorescent antibody technique permitted the rapid differentiation of all Rhizobium strains used, either from mixed inocula or from nodules. The doubly labelled antibiotic resistant mutants were inferior in terms of competitive ability for nodulation with an ineffective strain compared with the 'wild-type' parent strains. A rapid method for evaluating effective antibiotic resistant strains for nodulating competitiveness is suggested. All the mutants examined were also found to be less symbiotically effective than the respective 'wild-type' strains although these differences generally did not reach statistical significance. The reduced symbiotic effectiveness of the antibiotic resistant mutants was associated with an increase in magnitude of the variances for shoot dry weights, relative to that shown by the parent strains. A possible explanation for this phenomenon is presented.     

Analysis of intraspecific and interspecific variation in the genus Alternaria by the use of RAPD-PCR

The RAPD-PCR profiles of 13 phytopathogenic Alternaria species and two closely related outgroups were examined using six different primers. Each species produced a distinct pattern of DNA fragments which were used as a measure of the degree of relatedness between species. A. brassicae isolates of diverse origin showed high levels of similarity but little similarity was noted between other species. The closest interspecific genetic distances were recorded between A. citri, A. alternata and A. longipes. The outgroup genera Embellisia and Stemphylium, which are recognised as distinct, could not be clearly separated using RAPD banding criteria, suggesting a high level of genetic diversity amongst these groups of fungi.     

Gamete Release at Low Tide in Fucoid Algae: Maladaptive or Advantageous?

This review discusses three questions pertaining to gamete releaseby fucoid algae at low tide: 1) Are gametes viable and doesfertilization occur at low tide?, 2) How many gametes are releasedat low tide versus at high tide? and 3) Is gamete release atlow tide maladaptive or is it selectively advantageous? Gameterelease at low tide (LT) in fucoid algae is observed commonlyin monoecious species from the lower and mid-intertidal zones(e.g., Fucus distichus, F. evanescens, F. gardneri, Pelvetiacompressa); in dioecious species, intact antheridia (containingsperm) are commonly released at low tide (e.g., in Ascophyllumnodosum, F. vesiculosus). Fertilization at low tide can be determinedwith a calcofluor white assay and occurs in at least three species(F. distichus, F. gardneri, P. compressa). In general, fucoidalgae have high levels of fertilization success, but substantialmortality occurs during early embryogenesis in some intertidalzones due to physical stresses. The agarose bead assay is usefulto assess desiccation on an egg-sized scale. Constitutive dehydrin-likeproteins are present in sperm, eggs, and embryos. The releaseof gametes at low tide appears to be a consequence of a mechanismselected to permit gamete release under calm conditions in seawater;this mechanism is described. The timing of adhesion by zygotesat low and high tide is unknown. Such information and additionaldata on the relative proportions of zygotes produced by moneciousspecies at low tide versus high tide are required in order toassess effects of gamete release at low tide upon dispersaland population structure.     

Short‐term temperature change may impact freshwater carbon flux: a microbial perspective

Small freshwater bodies are abundant and economically and ecologically important on a global scale. Within these, protozoa play an important role in structuring planktonic food webs and sequestering CO₂. We hypothesized that short‐term (～20 days) fluctuations, of 2–10 °C, will significantly alter carbon flux associated with predator–prey interactions within the microbial planktonic food web. We examined the model ciliate, Urotricha farcta, which is abundant and common; it was fed the autotrophic flagellate Cryptomonas sp., which is also common. Laboratory experiments were conducted over relevant ranges: 8–24 °C; 0–2 × 10⁵ prey mL^?1. Mechanistic‐phenomenological multiple regressions were developed and fit to the data to obtain relationships for (1) growth rate and volume changes of the flagellate vs. temperature and (2) growth rates, grazing, and cell volume change of the ciliate vs. temperature and prey concentration. Responses revealed interaction between temperature and prey levels on all ciliate parameters, indicating it is inappropriate to apply simple temperature corrections (e.g. Q₁₀) to such functions. The potential impact of such temperature changes on carbon flux was illustrated using a simple ciliate–flagellate predator–prey model, with and without the top grazer, Daphnia, added. The model indicated that predator–prey pulses occurred over 20 days, with the ciliate controlling the prey population. For ciliates and prey, carbon production peaked at 20 °C and rapidly decreased above and below this maximum; differences between minimum and maximum were approximately fourfold, for both prey and ciliate, with low levels at 25–30 °C and 10–15 °C. Including literature data to parameterize, the influence of the grazer Daphnia did not alter the prediction that the ciliate may control short‐term flagellate pulses and temperature will influence these in a nonintuitive fashion.     

Disease spread of non-specialised fungal pathogens from inoculated point sources in intraspecific mixed stands of cereal cultivars

Spread of Septoria nodorum from inoculated point sources was examined in pure stands and mixtures of two spring wheat cultivars Kolibri and Maris Butler. Gradients in disease were observed soon after inoculation; the presence of the more resistant cultivar (Maris Butler) in the mixtures retarded the outward spread of disease compared with the susceptible pure stand (Kolibri). Regression analysis suggested that gradients in incidence were influenced by nearness to the source whereas gradients in severity were not. Spread of disease was also examined in pure stands and mixtures for the host/pathogen combinations, winter wheat (cvs Maris Huntsman and Maris Ranger)/S. nodorum and winter barley (cvs Maris Otter and Hoppel)/Rhynchosporium secalis. In contrast to the spring wheat experiment, no gradients were observed; explanations for the uniform distribution of disease were (a) extensive spread prior to the period of assessment, (b) no physical barrier to dispersal due to the juvenile growth stage of the crop and (c) exhaustion of the point-source.