Hematozoa from Mammals of South Vietnam*

SYNOPSIS. Blood smears from 519 mammals of South Vietnam were examined for hematozoa. Trypanosomes were found in Rattus norvegicus, R. exulans, R. nitidus, and Rattus sp. Hepatocystis vassali occurred in squirrels Callosciurus flavimanus; erythrocytic stages and liver merocysts were seen. Fruit bats Cynopterus brachyotis and one insectivorous bat Hipposideros larvatus, harbored closely related but as yet unidentified hemosporidia. Piroplasms were found only in carnivores: ferret-badgers Melogale personata, palm civets Paradoxurus hermaphroditus, and mongooses Herpestes javanicus.     

In situ bait plants as a method for detecting red core in strawberry fields

The spread of strawberry red core root disease (Phytophthora fragariae) from a heavily infested field with a history of 40 yr continuous strawberry growing, to and across an adjacent field where strawberries had never before been grown, was charted by growing bait plants of the highly susceptible alpine strawberry ‘Baron Solemacher’ at the intersections of an 8 m grid. Initially the fungus could not be detected by a soil sampling/glasshouse baiting test or in field grown baits, but after a very wet winter it was detected in the field grown bait plants. Most infections occurred in plants growing in a shallow depression running the length of the field, receiving drainage water from the higher infested site and where there had been standing water for much of the winter. The importance of topography was further demonstrated when baits were planted at commercial densities in two small areas of the field, one adjacent to and the other 18 m distant from the central depression. In the former many plants were infected within 2 months of planting whilst in the latter bait plants remained free of the disease for at least 18 months. The highly susceptible bait plants may be suitable for monitoring the health of commercial propagation stocks; they are easily propagated from seed and as they do not runner there is little hazard to stock purity.     

Cadmium in freshwaters: concentrations and chemistry

SUMMARY. 1. Concentrations of cadmium are reported for twenty largely unpolluted freshwaters in north-western England. They range from 15 to 117 ng l⁻¹ total Cd in the rivers and streams and from 18to51 ng l⁻¹ in the lakes, lying on the low side of values reported in the literature. The care required to obtain reliable data is stressed.
2. A comparison is made between the fraction of Cd found to be particulate (>0.2 μm) and that which is calculated to be adsorbed on particulate matter. This provides further insight into the speciation of Cd, as well as a test of the application of a simple adsorption model to the prediction of the observed speciation.
3.The adsorption model is found to be a poor predictor of the measured fraction of particulate Cd. Possible reasons for this are explored and the potentially important role of slow desorption kinetics is emphasized.     

A Comparison of Abscission of Rubber (Hevea brasiliensis) Leaves Infected with Microcyclus ulei with Leaf Abscission Induced by Ethylene Treatment, Deblading and Senescence

Studies on the histology and on effects of growth substancesand phenols as well as changes in activities of pectinmethylesterase indicated that the mechanism of abscission of Hevealeaflets infected with Microcyclus ulei differed from the mechanismof abscission of debladed, ethylene treated and senescent leaves.An abscission layer which was formed during abscission of debladed,ethylene-treated and senescent leaves was absent during abscissionof heavily diseased leaves. The ratio of pectinmethyl esteraseactivities in tissues distal to the abscission zone to activitiesin tissues proximal to the zone decreased in debladed and ethylenetreated leaves but such decreases were not detected during abscissionof Hevea leaves infected with M. ulei. Hevea brasiliensis Muell. Arg., rubber, leaf abscission, Microcyclus ulei, ethylene, indol-3-ylacetic acid, kinetin     

Changes in the Petiole of Leaves of Manihot esculenta (Crantz), on Rooting

The effects of age of leaf and of application of synthetic hormoneon the ability to produce roots, were investigated in leavesof Manihot esculenta. It was found that the age of the leafwas not critical to the process, but that the application ofhormone resulted in an early and prolific production of roots. The anatomy of the rooted petiole was investigated and was foundto differ from that of an unrooted petiole in three respects:in an increase in the amount of secondarily produced tissues;in the incomplete lignification of the secondary xylem and inthe production of adventitious roots from the interfascicularregions of the basal end.     

Indices of condition in tropical ruminants*

Bone marrow dry weight expressed as a percentage of its fresh weight was found to be a good indication of its fat content in wildebeest, kongoni, and buffalo. The calculated regression equations were similar enough to suggest a more general formula for the larger ruminants. Bone marrow fat is mobilized after the kidney fat and hence is a better measure of condition when an animal is under more extreme stresses. Fluctuations in kidney fat reflect physiological events related to reproduction. Visual estimates of bone marrow were found to reflect true differences in fat content, and the method is useful when marrow samples cannot be collected readily. It is pointed out that estimates of condition of naturally dying wild animals must be obtained before primary and secondary causes can be identified.     

A cytological analysis of the antimetabolite activity of 5-hydroxyuracil in Vicia faba roots

The effects of 5-hydroxyuracil (5-HU) (isobarbituric acid) upon cell elongation, mitosis, and DNA synthesis were studied in Vicia faba roots. 5-HU had no consistent effect upon root elongation. It blocked DNA synthesis (analyzed by photometric measurements of Feulgen dye in nuclei) during the first 6 hours of treatment; the block spontaneously disappeared by the 12th hour of treatment. Uracil and thymine had no effect upon this block of synthesis. Both thymidine and uridine reversed the block in 6 and 9 hours respectively. In all cases blockage of DNA synthesis was followed by inhibition of mitosis (determined by changes in the percentage of cells in mitosis) and resumption of DNA synthesis was followed by resumption of mitosis. Inhibition indices calculated from the mitotic data indicated a competitive relationship between 5-HU and thymidine and 5-HU and uridine. 5-HU is considered to block DNA synthesis by competing with thymidine for sites on enzymes involved in the synthesis. It is suggested that uridine reverses the block in synthesis by undergoing a conversion to thymidine.     

Changes in feeding habit as caterpillars grow

Abstract.

• 1 200 of 1137 species of British microlepidoptera make a single marked change in feeding habit as they grow.
• 2 Most numerous are species that change from leaf mining to one of case bearing, spinning, tying and rolling or concealed feeding, and species that change from concealed feeding to case bearing or spinning, tying and rolling.
• 3 Although in some instances numbers of closely related species make similar changes in behaviour, most changes observed are scattered among subfamilies.
• 4 Leaf miners have considerably smaller adults than concealed feeders, which themselves are smaller than external feeders and spinners, tiers and rollers. When case bearers are excluded from the analyses, species that remain as leaf miners or concealed feeders throughout larval development are on average smaller as adults than those that start out with these feeding habits but later change.
• 5 We suggest a number of reasons why larvae might make such fundamental switches.

     

Chloroplast DNA variability in old and recently introduced potato cultivars

Chloroplast DNA (cpDNA) variability has been examined in a range of tetraploid European potato cultivars. The potato genotypes studied included primitive cultivars such as Lumpers (1806), Yam (1836), Myatts Ashleaf (1847) and more recently bred cultivars such as Brodick (1990). Three cpDNA pheno-types were detected and these probably represent original introductions from South America into Europe. The most common cp phenotype was the T type cpDNA (Hosaka & Hanneman, 1988) characteristic of cultivars descended from cv. Rough Purple Chili. The presence of the T type cpDNA in the cultivar Yam indicates that this genotype which is of Andigena origin shares a common cytoplasm with other 5. tuberosum ssp. tuberosum clones which have a Chilean type cytoplasm. The implications of these results are discussed in relation to the origin of the T type cpDNA. Methods for increasing the cytoplasmic diversity of the cultivated potato gene pool are proposed.