Simulation study of the competitive ability of erect, semi-erect and prostrate cowpea (Vigna unguiculata) genotypes

Ecophysiological simulation models provide a quantitative method to predict the effects of management practices, plant characteristics and environmental factors on crop and weed growth and competition. The INTERCOM interplant competition model was parameterised, calibrated by monoculture data for three cowpea (Vigna unguiculata) genotypes that differed in growth habit, common sunflower (Helianthus annuus) and common purslane (Portulaca oleracea), and used to simulate competition of cowpea cover crops with sunflower or purslane. The simulation results were compared with observations from field competition experiments in 2003 and 2004. INTERCOM more accurately simulated actual field data for the competition of cowpea genotypes and sunflower than companion field experiments for the competition of cowpea and purslane. The validated simulation model of cowpea and sunflower at two densities was used to study the effects of cowpea growth habit on final biomass production of cowpea and sunflower. The model suggested that erect growth habit was more competitive than semi‐erect and prostrate growth habit, when cowpea genotypes were grown with sunflower. Cowpea leaf area distribution was important to higher cowpea biomass production, while cowpea height growth was important to reduce sunflower biomass. Our simulation approach is suggested as a method for crop breeders to gauge the likely success of selection for competitive crops before undertaking expensive long‐term breeding experiments.     

Age at death from natural scrapie in a flock of Suffolk sheep

This study deals with natural scrapie in a flock of Suffolk sheep being bred to maximise the incidence of the disease and shows that with succeeding generations the incubation period of the disease became progressively shorter until the flock died out. The most likely explanation for this phenomenon is considered to be an increase in the load of infection.     

The relative importance of traits reported in the first three gosford random sample tests

An analysis was performed on the published results of the first, second and third Gosford Random Sample Tests to determine which of the various biological traits reported had the greatest influence upon the overall ranking. Ten traits were considered. It was found that regression on survivors’ average egg production and laying house mortality removed 88.1 per cent of the variation in financial return. The addition of average egg weight and daily food consumption increased this figure to 93.3 per cent. The remaining traits, number of unsaleable birds at 500 days, body weight at 500 days, age at 50 per cent production, blood spots, meat spots and shell thickness, did not produce significant reductions except in so far as they were correlated with those previously mentioned.

The financial returns expected from improvements in the four important traits were:

• Per bird

• + 12 in survivors egg production 2S. 4¼d. ± 1¼d.

• —5 in percentage laying mortality is. 5d.± 1d.

• + 1 g. in average egg weight 10½d. + 1 ½d.

• —5 g. in food consumed per day 43/4d.± 1¼d.

Laying house mortality was found to be positively correlated among the entries with survivors’ average egg production and with average egg weight.     

GU-PCM2型控温式相变蓄冷冷藏车设计与空载性能试验

现有蓄冷冷藏车蓄冷装置多位于车厢顶部,存在重心偏高、不可控温等问题,基于此,该文设计了一款集相变蓄冷单元、车载制冷系统、隔热车厢、送风系统等于一体的GU-PCM2型蓄冷冷藏车。该蓄冷车将蓄冷装置独立设置于车厢前端并保温,系统利用夜间低谷电进行充冷,可在-25～10℃之间根据需要调控车厢温度。对蓄冷冷藏车厢设定温度为0和-18℃的2种工况进行空载温度场仿真与测试。结果表明,车厢内各测温点的模拟温度与实测温度均方根误差分别为0.7和0.8℃,最大绝对误差分别为1.1和1.2℃。冷藏车可有效控温10 h以上,车厢平均温度分别在1.1～2.9℃和-14.8～-16.9℃之间,波动范围为1.8和2.1℃,温度不均匀度系数在1.0以内。控温式蓄冷冷藏车与传统蓄冷车的对比试验结果表明,其平均温度波动值降低48.7%,温度绝对不均匀度系数降低50%以上,车厢质心较顶置式蓄冷车下降25.9%。研究结果可为蓄冷冷藏车的进一步优化设计与应用提供参考。     

Studies on the Motility and Cryopreservation of Rainbow Trout (Salmo Gairdneri) Spermatozoa

The very short duration of vigorous movement (1 1/2 to 7 min) in fresh water and physiological solutions make trout spermatozoa difficult subjects for cryopreservation studies. Solutions consisting of 250 to 280 mmol sucrose and 5 to 12% dimethyl sulphoxide (DMSO) (4 parts) did not activate trout spermatozoa (1 part), but after dilution with fresh water vigorous motility could be fully restored. These sucrose-DMSO solutions were employed in cryopreservation studies. Using straws and a fast freezing — fast thawing procedure, post-thaw dilution with fresh water resulted in 25%-60% of spermatozoa becoming motile, all with vigorous forward progression. Some existing methods for the cryopreservation of other freshwater fish spermatozoa were repeated on trout without success.     

A classification and evaluation of Irish water beetle assemblages

1. Modern records of 165 species of wetland beetle (Haliplidae, Hygrobiidae, Noteridae, Dytiscidae, Gyrinidae, Georissidae, Hydrochidae, Helophoridae, Hydrophilidae, Hydraenidae, Scirtidae, Dryopidae, Elmidae, Chrysomelidae, Curculionidae) were assembled for analysis. 2. Two hundred and eighty nine modern lists of seven or more species of water beetle from sites in Ireland were subjected to multivariate analysis. 3. Ten assemblage types were identified using TWINSPAN. Habitats typical of these assemblages are: A. deep rivers; B. rivers with riffles; C. puddles; D. canals and lakes with rich vegetation; E. ponds and ditches; F. turloughs; G. natural, minerotrophic fens; H. base-flushed cutover bogs; I. peat bogs; J. montane flushes. The distribution of these types is discussed. 4. Ordination of site data by DECORANA indicated that the important environmental variables dictating water beetle assemblage type in Ireland were: flow; water permanence; exposure; type of substratum. Acidity could not be isolated as a determinant, except within the analysis of assemblage types conducted using TWINSPAN. DECORANA isolated one brackish site as an outlier but salinity was not otherwise a major factor, probably because few brackish sites were included in the analysis. 5. The number of modern records for each species was used to provide a provisional set of species-quality scores. A simple rationale was devised to weight these scores in favour of relict species and against elusive species, species with short-lived adults and species primarily associated with man-made habitats. 6. The average species-quality score per site and the number of species recorded were used to rank sites within each TWINSPAN end-group. The most diverse sites with the highest quality were some turloughs, rich fens and base-flushed peat cutting complexes. Some montane lakes and flushes with relatively few species had high species-quality scores.     

The effect of fertility control on the transmission of bovine tuberculosis in wild brushtail possums

AIM: To determine the effect of fertility control on the rate of transmission of bovine tuberculosis (Tb), caused by Mycobacterium bovis, in brushtail possums (Trichosurus vulpecula).

METHODS: At two study sites with a history of Tb infection in the resident possum population, a sample of adult male and female possums (n=50), determined by palpation to be Tb-free, was surgically sterilised by gonadectomy. A sample of untreated Tb-free male and female possums (n=54) served as controls. Each study site was trapped every 2 months over a 3-year period, and the Tb status of the individuals in the trial assessed. At the conclusion of the trial, all remaining experimental individuals were killed, necropsied and examined for characteristic lesions typical of Tb. The rate of transmission of Tb infection was estimated using the incidence of tuberculous cases in the experimental animals and comparing it between sites, sex and sterilisation treatment.

RESULTS: Sterilisation by gonadectomy resulted in a reduction in the rate of transmission of Tb in male possums by 53%, but a corresponding increase in sterilised females for reasons that are still unclear. However, this interaction was statistically weak (p=0.10). When the sexes were combined, there was no overall effect of sterilisation on the rate of transmission of Tb (p=0.43). Sterility treatment notwithstanding, there was a highly significant difference in the rate of transmission between the sexes (p=0.01), being almost one order of magnitude higher in untreated males compared with untreated females.

CONCLUSIONS: Although lacking strong statistical support, these results suggest that fertility control that targets endocrine control of fertility may provide some additional benefits for disease control over that achieved by reductions in population density, by reducing the rate of transmission of M. bovis in male possums. However, additional studies are needed to confirm the validity of these results. The large difference in the rate of transmission of M. bovis in untreated males compared with untreated females suggests that transmission of Tb among males may be an important driver of the dynamics of Tb infection in possums.