Generation Time and Growth Rate of the Human Intestinal Parasite Blastocystis hominis

ABSTRACT. Blastocystis hominis , an anaerobic intestinal protozoan parasite of man, has a generation time (GT) in axenic culture of 8.5–19.4 h, depending on the strain tested. Average GT of the eight strains was 11.7 h. Zero growth time cell counts of 5.0 × 10⁵/ml to 2.0 × 10⁶/ml rose in 3–5 days to 1 × 10⁷ or 1 × 10⁸ cells/ml. The GT was determined for the 24-h period during which the most rapid growth occurred; about 2% of the B. hominis cells were in division during this time. Division under the culture conditions provided was by binary fission, the usual mode for B. hominis in vitro as well as in vivo. Division times were determined also by direct observation of individual dividing cells in slide cultures. These were usually ca. 40–60 min but sometimes as low as 20 min.     

The Effects of Light Intensity and External Potassium Level on Root/Shoot Ratio and Rates of Potassium Uptake in Perennial Ryegrass (Lolium perenne L.)

Loliun perenne L. (cv.S. 23) was grown on vermiculite in winterin a heated greenhouse for 8 weeks under factorial combinationsof two potassium regimes (nominally 6 parts/10⁶ and 156 parts/10⁶in Hewitt's solution) and three densities of artificially supplementedvisible radiation flux (36.1, 7.3, and 2.2 W m^–2). Growthand potassium uptake were studied through the calculation ofvarious growth functions from fitted curves. There was little effect of potassium treatment but the experimentalmaterial responded markedly to light. Leaf-area ratio in thethree treatments showed extreme plasticity in increasing from2–3 x 10^–2 through 6 x 10^–2 to 8–9 x10^–2 m² g^–1 as light intensity decreased. Correspondingdecreases in unit leaf rate, however, caused over-all reductionsin relative growth rate. Specific absorption rates for potassium (A_K, dry-weight basis)were strongly reduced at the lower light intensities but alsodisplayed complex ontogenetic drifts. Values of the allometricconstant, k (the ratio of root and shoot relative growth rates),decreased from c. 0.7 at 36.1 W m^–2 through c. 0.3 at7.3 W m^–2 to a value not significantly different fromzero (P < 0.05) at 2.2 W m^–2. In material grown under the two higher light intensities a constantinverse relationship was found between the mass ratio of rootand shoot and the corresponding activity ratio. The resultsconform to this model: Mass ratio = –0.001+45.0 (1/activityratio) where activity ratio is expressed as specific absorptionrate for potassium (in µg g root^–1 h^–1)/unitshoot rate (rate of increase of whole-plant dry weight per unitshoot dry weight, in mg g shoot^–1 h^–1). The implicationsof this relationship are discussed.     

Grain yield and incidence of take-all (Ophiobolus graminis Sacc.) in wheat grown in different crop sequences

The yield of wheat and the incidence of take-all were measured in crops grown in six different 4-year sequences, repeated in 3 successive years. The first crop of winter wheat grown after oats or beans yielded 13–23 cwt/acre (1632–2887 kg/ha) more grain than wheat after wheat or barley. Spring wheat after oats yielded 2–5 cwt/acre (250–625 kg/ha) more than spring wheat after wheat. The smaller yields of wheat after wheat or barley were caused mostly by greater prevalence of take-all. Regression analysis indicates that each 1 % increase in straws with take-all decreased yield of winter wheat by 0·6%. Take-all was more prevalent in the second and third successive wheat crops after oats than in the fourth crop.     

Influence of crop background on natural enemies of aphids on Brussels sprouts

The most abundant natural enemies of aphids on Brussels sprout crops were Syrphidae, different species being attracted differentially to weedy or weed-free plots according to whether they were more host-plant-orientated (e.g. Melanostoma spp., Platycheirus spp.) and thus affected directly by the background, or more aphid-orientated (e.g. Syrphus balteatus) and so less affected by background than by aphid numbers. Oviposition by Melanostoma spp. was usually much greater in weedy sprout crops than on sprouts in bare soil, and their eggs were also very abundant on weeds. Eggs of other syrphid species were scarcer on weeds. In contrast to Melanostoma, Platycheirus spp. usually oviposted preferentially on sprouts growing in bare soil. Oviposition by S. balteatus was in response to aphid abundance and thus tended to become greater on sprouts in bare soil. Notably more adults of non-aphido-phagous Syrphidae were caught over weedy than over non-weedy Brussels sprout plants. Anthocoris nemorum nymphs and adults were very common on sprout plants and weeds in the weedy crop but were scarce on sprouts in bare soil; A. nemorum oviposited on white and yellow charlock (Raphanus raphanistrum and Sinapis arvensis) occasionally. Parasitism of Brevicoryne brassicae by Diaeretiella rapae appeared to be related to aphid numbers and was only indirectly influenced by the crop background. Field experiments with green and brown cloth backgrounds showed that some syrphids were attracted to green; A. nemorum was relatively scarce over both artificial backgrounds. It is concluded that decreased natural enemy action is partly responsible for the initially greater abundance of B. brassicae in a weed-free crop of Brussels sprouts than in a weedy crop.     

Seed structure and the taxonomy of the Cruciferae

The external morphology and anatomy of the seeds of some 90 genera and some 200 species of the Cruciferae have been investigated. Emphasis has been laid on the relationships of seed structure to taxonomy. As regards seed anatomy, the testa is probably of greatest value in determining taxonomic relationships. Seed structure supports the Cruciferae as a natural taxon. In the present investigation, few genera and species show seed characters which are either exclusive or very distinct. Of the remainder, most genera are distinguishable from each other on a permutation of their macroscopic and microscopic seed characters. However it is difficult or impossible to distinguish between some genera on seed characters. The present investigation provides no support for tribal divisions within the Cruciferae.     

Pyridoxine Kinase in Plasmodium lophurae and Duckling Erythrocytes*

SYNOPSIS. Pyridoxine kinase enzyme activity was greatly increased in duckling erythrocytes infected with Plasmodium lophurae. Pyridoxine kinase activity in parasites freed from erythrocytes was much greater than that of uninfected erythrocytes. The apparent K_m for pyridoxine of the parasite enzyme was 6.6 × 10^-5 M whereas the host red cell enzyme K_m was 1.9 × 10^-6 M. Deoxypyridoxine inhibited host and parasite pyridoxine kinase activity with an apparent K_i of 1.5 × 10^-6 and 8.6 × 10^-6 M, respectively. These results suggest that the vitamin B₆ metabolism of the malaria parasites is distinct and separate from that of the host erythrocytes.     

THE EFFECT OF CERTAIN SOIL TREATMENTS ON DIDYMELLA STEM ROT OF TOMATOES PART I. GLASSHOUSE EXPERIMENTS

When tomatoes were planted in steamed soil inoculated with spores of Didymella lycopersici Kleb., a large proportion became infected, but very few became infected in unsteamed soil similarly inoculated. In soil treated with formalin and subsequently inoculated the number of diseased plants was about half that in steamed soil. Reinfecting steamed soil with soil micro-organisms before inoculation with D. lycopersici reduced the amount of disease. Covering steamed soil with a layer of maiden loam filtered out a large proportion of D. lycopersici spores applied in water suspension and reduced the amount of disease. Addition of stable manure either before or after steaming did not affect the number of diseased plants. Steamed soil remained susceptible to infection by D. lycopersici for 4 months. D. lycopersici survived in a glasshouse soil over the winter, but the number of diseased plants was small. Cultivation may lessen the amount of disease by burying most of the infected surface layers of the soil. The peak of infection under glass occurred in May. The amount of disease and the yield were correlated, but with severe infection the yield varied with the time of infection and the distribution of diseased plants.     

Influences of two life‐history stages of the weevil,Larinus minutus,on its host plant Centaurea diffusa

1. We hypothesised that, for weed biological control, using species that feed as both adults and larvae would be advantageous. Here, we test the impacts of adult and larval feeding of Larinus minutus (Col.: Curculionidae), a successful biological control agent of diffuse knapweed, Centaurea diffusa (Asteraceae), in British Columbia, Canada. 2. At one site, the observations of the present study showed that the intensity of adult weevil feeding did not predict the level of larval attack. Experiments found no evidence for plant‐mediated competition between the life‐history stages. 3. At two sites and in two years, experimental manipulations of adult and/or larval feeding damage were conducted and plant performance measured. Neither antagonistic nor synergistic interactions occurred, but at each of the two sites a different life‐history stage was responsible for reduction in the number of seeds produced by the plants. 4. Although one of the two different feeding modes was redundant at each site, the ability of adults and larvae to reduce plant performance in different areas makes the species effective in a wider range of environments.     

Ophryocystis elektroscirrha sp. n., a Neogregarine Pathogen of the Monarch Butterfly Danaus plexippus (L.) and the Florida Queen Butterfly D. gilippus berenice Cramer1

SYNOPSIS. Naturally occurring populations of the monarch butterfly, Danaus plexippus (L.) and the Florida queen butterfly D. gilippus berenice Cramer were found infected with Ophryocystis elektroscirrha sp. n. This neogregarine pathogen infects the hypodermal tissue, remains in micronclear schizogony until after pupation of the host, and then rapidly completes morphogenesis in the tissue that becomes the scales of the adult butterfly. The adult thus carries the spores externally; no internal infection was detected. The pathogen is unique in the genus Ophryocystis because: other species have all been reported from the Malphigian tubules of Coleoptera; no pseudopodial attachments of schizonts to host tissue were seen; the merozoites were motile; the cystic membrane surrounding the zygote was tenuous, and the sporont developed with no apparent membrane other than the spore wall: and the spore wall appeared amber in transmitted light when morphogenesis was completed.