Inoculation of lactating ewes by the intramammary route with Mycoplasma agalactiae: comparative pathogenicity of six field strains

Contagious agalactia affects goats and sheep. In most infected sheep, the causal agent, Mycoplasma agalactiae, induces mastitis and/or agalactia, keratoconjunctivitis and arthritis. However, a few strains of M. agalactiae were isolated from tank milk from flocks without any clinical signs. The present study was undertaken to compare these apparently "asymptomatic" strains to classical virulent strains in order to assess the pathogenicity of four "asymptomatic" strains. Six groups of lactating ewes were inoculated by the intramammary route with 10(8) viable mycoplasmas of each strain. The clinical signs were regularly evaluated; the excretion of bacteria in milk and the serological response were measured. Ewes were necropsied 7 weeks after inoculation and the level of infection in retromammary lymph nodes was determined. Among the 4 apparently "asymptomatic" strains, 2 were fully virulent as were the strains isolated from discased animals, and the other 2 induced somewhat less severe clinical symptoms. The other parameters, in particular the level of excretion in milk and the level of infection of regional lymph nodes following necropsy were similar for all strains. Mean antibody response was also comparable between the apparently "asymptomatic" and virulent strains, in spite of great individual variability. This observation shows that flocks without any clinical sign from which M. agalactiae is isolated in bulk milk, must be kept under strict control since mycoplasmas may induce severe outbreaks later with changing conditions of breeding.     

Transmission ofPhytophthora infestans in cut potato seed

One or two cycles of late blight transmission may occur in cut potato seed between cutting and emergence. If seed are not planted immediately, mycelium from diseased pieces can infect across adjoining cut surfaces within 8 hr. Sporangia production begins on freshly cut diseased tubers in 1–2 days, on mycelium-infected seed pieces within 4–5 days, and on spore-infected seed pieces in about 1 wk. These spores are further dispersed during handling and planting, and may infect contaminated seed in the ground, regardless of suberization. Sporangia can be transferred to healthy tubers on cutting knives, although this appears infrequent. The risk and degree of secondary spread increase with the length of time cut seed are held before planting. Such secondarily infected seed are more likely to survive and produce infected stems than the original infected tubers. Treatment of seed with appropriate fungicides immediately after cutting substantially reduces or prevents transmission of late blight to healthy seed. Certain seed treatments withoutPhytophthora-specific components may increase the risk of tuber blight.     

Enrichment of logging gaps with moabi (Baillonella toxisperma Pierre) in a Central African rain forest

Studies of regeneration in African rain forests suggest that without silvicultural treatments, natural succession in logging gaps may not result in the establishment of timber species. In this paper we present the results of an experimental enrichment planting with moabi (Baillonella toxisperma Pierre), a valuable and important timber species harvested in Central Africa. Although forest gaps are generally considered as favourable for the regeneration of this species, a survey conducted in a forest concession in south-eastern Cameroon provided an estimate of only 12.7 seedlings ha⁻¹, suggesting that the species was, in fact, poorly represented in logging gaps within the study area. To further investigate the dynamics of the moabi in logging gaps, 795 seeds were sown in 15 logging gaps and 410 nursery-raised seedlings were planted in 15 other gaps. A biannual monitoring program over a 30-month period showed a lower survival rate for seedlings from sowing (75.9%) compared to that of nursery-raised seedlings (95.3%). Planted seedlings reached an average of 229.3 cm tall whereas seedlings from sowing were 167.5 cm tall, with the observed difference roughly corresponding to the average height of the nursery-raised seedlings at the time they were introduced to the logging gaps. After 30 months, the diameters of planted seedlings (16.8 mm) were also greater than those of the directly sown individuals (12.5 mm). Forest gap characteristics significantly influenced the growth of the plants. Factors accounting for the differences were total solar radiation, the soil content of coarse sand, the topographic position of the gap, the vegetation cover and the density of Macaranga spp. Whilst total solar radiation had a positive influence on growth, the remaining factors had impacted growth negatively. A streamlined technique was tested by planting 7 seedlings in 250 gaps. Without additional site maintenance, 29.3% of the moabi seedlings emerged naturally from the competing vegetation after 24 months. With biannual maintenance some 89.4% of seedlings became successfully established. Clearance operations had no significant influence on the height of plants whilst plant diameter was greater in cleared gaps. The total cost of the enrichment technique was 5.5 EUR per gap without maintenance and 7.5 EUR per gap with a single maintenance measure. Whilst long-term monitoring is needed, this study suggests a high survival rate of moabi introduced in logging gaps, and a growth rate 10 times higher than previously reported under canopy cover. These findings, combined with the low costs of the enrichment technique, support the use of silvicultural measures in logging gaps to restore the forest.     

Long-term agroecosystem experiments: assessing agricultural sustainability and global change

Long-term agroecosystem experiments can be defined as large-scale field experiments more than 20 years old that study crop production, nutrient cycling, and environmental impacts of agriculture. They provide a resource for evaluating biological, biogeochemical, and environmental dimensions of agricultural sustainability; for predicting future global changes; and for validating model competence and performance. A systematic assessment is needed to determine the merits of all known experiments and to identify any that may exist in tropical and subtropical environments. The establishment of an international network to coordinate data collection and link sites would facilitate more precise prediction of agroecosystem sustainability and future global change.     

Quaggy Joe: A high-yielding, round, white potato variety for fresh market

The Quaggy Joe potato variety is high-yielding and medium to medium-late maturing with attractive, round-oval, white-skinned, white-fleshed tubers with medium-shallow pink eyes. Its major use is expected to be as a maincrop tablestock variety. Quaggy Joe is resistant to the potato leafroll virus, and is also moderately resistant to early blight (Alternaria solani), dry rot (Fusarium sambucinum), and soft rot (Erwinia carotovora subsp.carotovora). Quaggy Joe tubers have shown very little shatter or blackspot bruising, but sprout earlier than Atlantic. Young plants have shown sensitivity to the herbicide metribuzin.     

THE POSITION IN THE PLANT AND THE DATE OF ORIGIN OF TILLERS WHICH PRODUCE INFLORESCENCES

The dates of their first appearance and the dates of flowering were recorded monthly over three years from time of sowing for all tillers produced by S215 meadow fescue plants growing in simulated sward conditions in large concrete pots outdoors. The results are expressed and discussed in terms of the percentage contribution of inflorescences by tillers in relation to their chronological and ontogenetic age. The latter appeared the more important. The major contribution of inflorescences was made by primary tillers in the first harvest year, by secondary and tertiary tillers in the second year and by tertiary and quaternary tillers in the third year. The chronological age at which tillers could flower ranged from 3 to 33 mouths.     

Digestive retention times for Allen's swamp monkey and L'Hoest's monkey: data with implications for the evolution of cercopithecine digestive strategy

Primates access energy from plant fiber via bacterial fermentation in either a modified forestomach ('foregut'), a caecocolic ('hindgut') chamber of the large intestine, or both. Longer digestive retention times allow for more complete fermentation; as such, primates that consume an herbivorous diet high in fiber are expected to have both relatively and absolutely longer retention times than those mammals that rely on more readily digestible plant foods, such as fruit. We used particulate markers to measure the digestive retention times of captive Allen's swamp monkeys [Allenopithecus nigroviridis (Pocock, 1907)] (n= 3) and L'Hoest's monkey (Cercopithecus lhoesti P. Sclater, 1899) (n= 2). Results indicate mean retention times of 23.2-29.4 h and 23.2-24.0 h for C. lhoesti and A. nigroviridus, respectively. Results from this study, in combination with previously published data on digestive retention times in other primate species, indicate that cercopithecines differ from other primate taxa by having lengthier retention times that can be predicted by body mass alone. These data are consistent with the hypothesis that relatively lengthy retention times are a primitive trait for Cercopithecinae.     

A gene expression map of the Arabidopsis root

A global map of gene expression within an organ can identify genes with coordinated expression in localized domains, thereby relating gene activity to cell fate and tissue specialization. Here, we present localization of expression of more than 22,000 genes in the Arabidopsis root. Gene expression was mapped to 15 different zones of the root that correspond to cell types and tissues at progressive developmental stages. Patterns of gene expression traverse traditional anatomical boundaries and show cassettes of hormonal response. Chromosomal clustering defined some coregulated genes. This expression map correlates groups of genes to specific cell fates and should serve to guide reverse genetics.