The growth, yield and nutrient uptake of winter wheat following root-pruning

The effect of root-pruning on shoot growth was investigated in winter wheat growing in lysimeters. Removal of half of the root axes at the beginning of stem elongation reduced shoot dry matter, determined 1 month after pruning, by 13% and grain yield by 8%. Removal of either the seminal or nodal root system during tillering reduced shoot dry weight, measured during the growing season, by 7% and grain yield by 25%. Root-pruning had negligible, or only transient, effects on the concentration of nitrogen, phosphorus, potassium, magnesium and manganese in the shoots. The harvest index was not affected by root-pruning.     

草鱼血液的研究

本文报道了212尾池养草鱼Ctenopharyngodon idellus的血液中红细胞数、自细胞数、血红蛋白值、红细胞脆性值、比积及比重值、血细胞沉降率、白细胞分类计数和各型血细胞体的大小等正常数值和上述常数值在雌雄个体上的差异,以及鱼体年龄和繁殖季节产卵前后的差异等,为草鱼血液的常数值提供了较为系统的资料。     

Pseudomonas tolaasii in mushroom (Agaricus bisporus) crops: activity of formulations of 2-bromo-2-nitropropane-1,3-diol (bronopol) against the bacterium and the use of this compound to control blotch disease

The bactericidal activity of 2-bromo-2-nitropropane-1,3-diol (bronopol) against Pseudomonas tolaasii , the causative organism of mushroom bacterial blotch, is enhanced by the addition of Tween 80, EDTA and phenylethanol. Results of tests with this pseudomonad confirm that bronopol is more active in alkaline solutions and enhancement of the bactericidal activity of this compound can be obtained by adding calcium carbonate, or mushroom casing (limestone and peat). Quantitative observations show that sterility can be achieved with bronopol at 100 µg/ml in 24 h following artificial inoculation of casing with Ps. tolaasii in glass flasks. On miniature mushroom beds in controlled environments a single application of bronopol, in tap water during routine watering, controls bacterial blotch disease. Bronopol is a slow-acting bactericide, destroying Ps. tolaasii in mushroom casing and effecting control of bacterial blotch disease.     

Pathogenic variability of downy mildew (Sclerospora graminicola) on pearl millet. I. Host cultivar reactions to infection by different pathogen isolates

Cultivars of pearl millet were challenged by isolates of downy mildew collected from various locations in West Africa and India in order to ascertain whether variability in cultivar response was genetically or environmentally determined. Results of experiments, in Polythene tunnels which imitated tropical field conditions, were confirmed by more precise experiments in an isolation plant propagator. The most important conclusion was that variation is determined by host and pathogen genotypes. West African isolates of the pathogen were generally more pathogenic than Indian isolates. However, there were also substantial differences between two isolates collected from different host cultivars at the same location in Upper Volta. Cultivar ICH105 differentiated between West African and Indian isolates. Cultivars 700516 and MBH110 also showed differential responses between isolates. In contrast two distinct types of symptom expression were recorded and found to be characteristic of cultivar genotype, independent of pathogen isolate. The possibility that both race specific and race non-specific resistance may coexist in this little understood pathosystem is discussed and the practical implications are considered.     

Evidence for a Calcium/Calmodulin Involvement in Density-Dependent Melanogenesis in Murine B16 Melanoma Cells

Previous work from our laboratory has shown that both cyclic AMP and calcium/calmodulin appear to be involved in the regulation of melanogenesis in murine B16 melanoma cells. In these cells as in murine Cloudman S91 cells, melanogenic responsiveness to melanocyte-stimulating hormone (MSH) varies with cell density in culture. Our objective in this study was to learn more about the intracellular systems involved in the control of melanogenesis, particularly the role played by calcium. The melanogenic response to αMSH was compared to the response to drugs affecting intracellular free calcium and calmodulin over a range of cell densities in B16F1 cells. αMSH-stimulated melanin production was extremely density-dependent but αMSH-stimulated cyclic AMP production was independent of cell density. The melanogenic response to agents that increased intracellular calcium (A23187) or inhibited intracellular calmodulin varied with cell density. A drug (TMB8) that lowered intracellular free calcium, however, increased melanogenesis independently of cell density. At high cell density it was found that an elevation in calcium decreased melanogenesis, whereas agents that reduced calcium or inhibited calmodulin activity increased melanogenesis. At low cell density, however, the inhibitory response to A23187 was lost and in some experiments even stimulated melanogenesis. These data suggest that the calcium/calmodulin signalling system has an inhibitory influence on melanogenesis, and its expression, which depends upon cell density, may also modulate the response to stimulatory agents such as αMSH.     

Wintering site fidelity and movement patterns of Western Sandpipers Calidris mauri in the San Francisco Bay estuary

Western Sandpipers Calidris mauri are the most numerous shorebird species in the San Francisco Bay estuary during winter. A sample of 106 Western Sandpipers was captured in mist nets and radio-marked with 1-g transmitters to examine their wintering site fidelity and movements. Differences in distances moved, home range extent and core area size were examined by age, sex, season, site, time of day and tide. All birds remained in the south San Francisco Bay region during winter and exhibited strong site fidelity, with a mean home range of 22.0 km² or only 8% of the study area. First-year birds had larger home ranges (26.6 ± 3.6 km²) than adults (17.2 ± 2.5 km²) in winter, but home range sizes of males and females were not significantly different in any period. Home range sizes were similar between seasons, but core areas were smaller in spring (6.3 ± 1.2 km²) than in early (9.6 ± 4.0 km²) or late (11.6 ± 1.6 km²) winter. Movements and home range size were similar for radio-marked birds located during day and night. The high degree of regional and local site fidelity demonstrated that the mixture of natural mud fiats and artificial salt ponds in southern San Francisco Bay provided sufficient resources for large wintering populations of Western Sandpipers.     

Fine Structure of Oocyst Transformation and the Sporozoites of Leucocytozoon dubreuili*

SYNOPSIS. The sporogonic stages of Leucocytozoon dubreuili in the midgut and salivary glands of the simuliid vectors was studied by electron microscopy. Young uninucleate oocysts have a pellicle that initially resembles that of the ookinetc. Numerous electron-dense bodies and microtubules in the peripheral cytoplasm may be involved in the formation of the cyst wall. The dense bodies appear to give rise to the amorphous material of the wall. The tubules which run circumferentially beneath the oocyst's boundary probably serve as a skeletal support for the cell surface during deposition of the wall material. A subcapsular “space” which provides area for expansion of the developing sporozoites is formed in early multinucleate oocysts. The subcapsular “space” appears to be formed through a condensation of the peripheral cytoplasm, resulting in an osmotic gradient across the oocyst's limiting membrane. Consequently water diffuses out, creating a fluid-filled space. Sporozoite formation begins with localized thickenings on the oocyst's limiting membrane. Subsequent extension of the thickened regions into the subcapsular “space” marks the onset of sporozoite budding. The process is highly synchronized, and culminates with the production of up to 150 sporozoites about the sporoblastoid body. The structure of sporozoites from mature oocysts and of the salivary glands of the vector is basically similar, although salivary gland sporozoites are more elongate and have numerous electron-dense micronemes. The paired rhoptries in the latter sporozoites are more elongate and uniformly electron-dense than in oocyst sporozoites.     

Provisioning habitat with custom‐designed nest‐boxes increases reproductive success in an endangered finch

Manipulating resource availability to assess the strength and effects of resource limitation on an animal population is relatively straightforward, and thus, common in the scientific literature. Resource quality, however, is rarely manipulated, as this requires a priori knowledge of a relationship between some measurable variation in the resource and individual preference and/or fitness. Recent research on nest‐site selection was used to inform the design of custom‐built nest‐boxes for an endangered hollow‐nester, the Gouldian finch (Erythrura gouldiae). By provisioning breeding populations with these ‘high quality’ artificial nest sites over 3 years, we experimentally investigated the strength and effects of nest‐site limitation in this species. Breeding pairs using nest‐boxes initiated nesting earlier, produced larger clutches and fledged more offspring per season than those in natural hollows. Total and mean reproductive output also increased in nest‐box provisioned sites over the duration of the study. All of these effects were predominantly driven by pairs initiating clutches earlier, potentially because of the reduced intra‐ and interspecific competition for nest sites at optimal breeding times. Our findings suggest that reproduction in wild Gouldian finch populations may be limited by the availability of high quality nest sites in the landscape, and that nest‐boxes could be used as a tool for enhancing reproduction in recovering populations. Furthermore, we conclude that resource quality is equally, if not more important than quantity when supplementing resource‐limited habitats.     

不同生态型摩西球囊霉菌株对蜈蚣草砷吸收的影响

砷超富集植物——蜈蚣草无论是在野外或是在室内均能被丛枝菌根真菌(AM真菌)侵染,但其对蜈蚣草砷吸收及转运的机理尚不清晰.本研究将分离于湖南省郴州市金川塘某铅锌尾矿蜈蚣草根际土壤(Glomus mosseae BGC GD01,简称污染菌株)和云南省未污染土壤(G.mosseae BGC YN05,简称非污染菌株)的2种摩西球囊霉菌株分别接种于非污染生态型和污染生态型蜈蚣草根际,8周后利用菌根化蜈蚣草幼苗在浓度为100 μmol·L-1砷(Na2HAsO4·7H2O)营养液中进行为期24 h的水培试验.结果表明,2种生态型摩西球囊霉菌株分别与蜈蚣草形成中等程度侵染,侵染率为25.2％ ～31.3％.无论是接种污染菌株或是非污染菌株,均明显促进了蜈蚣草根部对磷的吸收.在24 h水培试验期间,接种非污染菌株显著促进了蜈蚣草根部砷的吸收,但接种污染菌株对蜈蚣草根部砷吸收的促进作用有限,说明AM真菌对蜈蚣草砷吸收存在种内差异.