Epilithic biofilm as a key factor for small‐scale river fisheries on Caribbean islands

Abstract Numerous freshwater species are consumed or exploited through artisanal fisheries in the rivers of the islands of Guadeloupe, French West Indies. Autochthonous production of organic matter is limited in these flowing rivers and is mainly represented by scarce filamentous green algae and an abundant epilithic biofilm growing on wet stones in the river bed. Stable isotope analysis was used to quantify the relative importance of biofilm and other riverine allochthonous and autochthonous food sources in the diet of tropical shrimps (Palaemonidae, Atyidae and Xiphocarididae) and fishes (Gobiidae and Eleotridae) consumed by the local people. The epilithic biofilm was exploited by most species, constituted an important source of autochthonous carbon and was an important source of organic matter production at the base of freshwater food webs in Caribbean rivers. Biofilm percentages in the diet reached 32% for molluscs, 85% for atyid shrimps, 29% for xiphocaridid shrimps, 14% for palaemonid shrimps and 13% for fish. Assessment of biofilm in nine rivers showed that blue and red cyanobacteria were quantitatively dominant with a moderately rich diatom flora. These results address the interactions between river biofilm and Caribbean freshwater fauna where trophic links between consumers and their potential resources have poorly been documented.     

新《兽药管理条例》实施过程中存在的难点

介绍了新<兽药管理条例>在当前兽药管理实践中存在的难点和问题,提出了解决这些问题的建议和措施.     

Effect of stale seedbed preparations and subsequent weed control in lettuce (cv. Iceboll) on weed densities

The effects of stale seedbed preparations and several weed control methods on the emergence of weeds in lettuce were studied. The specific goal was to evaluate the use of a stale seedbed in combination with chemical or mechanical weed control methods in the field. Depending on location and year, stale seedbed preparations followed by weed control prior to planting reduced the amount of weeds during crop growth by 43–83%. Control of the emerged seedlings after a stale seedbed preparation was more effective with glyphosate than with a rotary harrow. Covering the rotary harrow during control to prevent light reaching the soil improved its effect on the weed density during crop growth in two of 3 years. Radiation with far red light (FR) did not reduce the number of emerging weeds in this study. Mechanical control by finger weeder, torsion weeder and hoe was applied without stale seedbed preparations. These measures reduced the weed densities by 88–99%, compared with the untreated control and were more effective than chemical weed control with carbetamide and chlorpropham. The results show that the stale seedbed technique in combination with mechanical control of emerging weeds can reduce the weed population during crop growth as effectively as chemical control. The technique may therefore help reduce the use of herbicides in lettuce crops in the future.     

匈牙利半湿润气候地区田间尺度下土壤侵蚀引起的土壤有机碳再分布

Soil organic carbon(SOC) has primary importance in terms of soil physics, soil fertility and even of climate change control. One hundred soil samples were taken from an intensively cultivated Cambisol to quantify SOC redistribution triggered by soil erosion under a subhumid climate, by the simultaneous application of diffuse reflectance(240–1 900 nm) and traditional physico-chemical methods.The representative sample points were collected from the solum along the slopes at the depth of 20–300 cm with a mean SOC content of 12 g kg~(-1). Hierarchical cluster analyses were performed based on the determined SOC results. The spatial pattern of the groups created were similar, and even though the classifications were not the same, diffuse reflectance had proven to be a suitable method for soil/sediment classification even within a given arable field. Both organic and inorganic carbon distributions were found to be a proper tool for estimations of past soil erosion processes. The SOC enrichment was found on two sedimentary spots with different geomorphological positions. Soil organic matter composition also differed between the two spots due to selective deposition of the delivered organic matter. The components with low-molecular-weight reached the bottom of the slope where they could leach into the profile, while the more polymerised organic matter compositions were delivered and deposited even before on a higher segment of the slope in an aggregated form. This spatial difference appeared below the uppermost tilled soil layer as well, referring the lower efficiency of conventional ploughing tillage in soil spatial homogenisation.     

Assessment of partial resistance of potato to, and pathotype and virulence differences in, potato cyst nematodes

Results are reported for several international collaborative experiments which examined methods of assessing degrees of partial resistance in potato and virulence in potato cyst nematode (PCN, Globodera pallida). It was demonstrated that absolute rates of multiplication can be extremely variable on both susceptible and partially resistant clones, even when the same population and test procedures are employed. It was therefore concluded that, on clones with quantitatively inherited resistance (i.e. partially resistant), absolute rates of multiplication cannot be used to separate pathotypes. Expression of these rates as percentages of those on the susceptible controls reduced the absolute differences between tests, but the values obtained were still too variable for statutory use. However, whatever the environment or nematode population used, it was observed that the resistance of the test clones and virulence of the nematode populations were generally ranked in a similar order. The main exceptions to this were: (1) a Petri-dish test where cv. Vantage was less resistant than in canisters or pots and (2) a pot test where cv. Darwina tended to be more interactive with environmental factors than the other test clones. It was also observed that with some populations of PCN in pots the susceptible cv. Bintje was a less good host than cv. Désirée. On the basis of these results it is suggested that certain partially resistant clones should be used as internal references in statutory, recommended list and breeders' assessment tests against which the resistance of the test clones are compared. For international comparability it is necessary that the different centres conducting such tests use the same reference clones and nematode populations, and similar test methods.     

Birth weight,birth type and pre-weaning survivability of West African Dwarf goats raised in the Dangme West District of the Greater Accra Region of Ghana

A study was conducted on 441 West African Dwarf goat (WADG) kids born from September 1999 to August 2002 at three locations in the Dangme West District of the Greater Accra Region in Ghana to determine the effect of environmental factors on birth weight, birth type and pre-weaning survivability. The overall mean birth weight was 1.32 ± 0.01 kg. Birth weights were similar (p >0.05) between single births (1.43 ± 0.04 kg) and twins (1.34 ± 0.03 kg), but singles were significantly heavier (p < 0.05) than triplets (1.24 ± 0.05 kg). Kids born in the major wet season recorded the best mean birth weight (1.37 ± 0.04 kg). Sex, parity of does, and year of birth of kids had no significant (p > 0.05) effect on birth weight. Mean litter size was 1.93 ± 0.03. Does that kidded in the dry season had a significantly (p < 0.05) higher litter size (2.05 ± 0.06) than those that kidded in the minor wet season (1.80 ± 0.10). Litter size of first-parity kids was significantly smaller (p < 0.05) than in subsequent parities. Litter size dropped significantly (p < 0.05) from year 2 (2.03 ± 0.07) to year 3 (1.83 ± 0.07). Pre-weaning survivability was 79.1% and season of kidding had a significant (p < 0.05) effect on survivability. Survivability of quadruplets (61.8%) was significantly (p < 0.05) lower than in the other birth types.     

Résistance des solanacées àGlobodera et influence de certains facteurs sur les résultats des tests de résistance1

La résistance àGlobodera rostochiensis et àG. pallida chez la quasi-totalité des clones de pommes de terre connus s'exprime essentiellement par un blocage du développement des larves L2 et, pour les individus qui parviennent a se développer, par une orientation préférentielle vers le phénotype mâle. Tout effet défavorable sur les nématodes accentue ces deux phénomènes. Certains effets, tels que la compétition intraspécifique, le vieillissement des larves et les interactions avec la population choisie comme inoculum standard, sont analysés. Il en ressort que, quel que soil le type de test pratiqué, en pots ou en boîtes de Pétri, il faut porter la plus grande attention à l'origine de l'inoculum et l'idéal est d'utiliser une population se développant bien dans les clones sans résistance. Ce choix fait, il convient de limiter les niveaux de compétition intraspécifique: en boîtes de Pétri, un effectif de cinq larves par racine est un optimum; en pots, une densité de 0,25 larves par g de sol est souhaitable. Pour les tests exécutés en boîtes de Pétri, il faut veiller á ne pas utiliser des larves conservées trop longtemps á basse température, condition classique de conservation qui diminue leur potentiel infectieux.