Changes in soil microflora associated with control of Sclerotium Rolfsii by Furfuraldehyde

The efficacy of 2‐furfuraldehyde for control of Sclerotium rolfsii was studied in laboratory and greenhouse experiments. Mycelial growth of the fungus was reduced proportionally with concentrations of 0.1–0.5 ml furfuraldehyde l^‐1 agar medium, and viability of sclerotia diminished on exposure to 2‐furfuraldehyde vapours. Detectable populations of bacteria and fungi, including Trichoderma spp., were reduced significantly (9=0.05) when furfuraldehyde was added to the agar used for soil dilution plates of untreated soil. Repeated treatments of natural soil with the fumigant significantly increased populations of Trichoderma spp. and bacteria, but diminished numbers of actinomycetes. Increasing dosages applied to soil artificially infested with S. rolfsii caused a reduction of disease on lentil, Lens culinaris. Results indicate that the compound, when applied to field soil, changes the composition of soil microflora and has potential for integrated control of S. rolfsii.     

A Comparison of the Efficacy of Nuclear Polyhedrosis and Granulosis Viruses in Spray and Bait Formulations for the Control of Agrotis segetum (Lepidoptera: Noctuidae) in Maize

Agrotis segetum nuclear polyhedrosis virus (AsNPV) and granulosis virus (AsGV), propagated in laboratory cultures of A. segetum in England and A. ipsilon in Spain, respectively, were applied to plots of maize plants at the one‐ to four‐leaf stage of growth. Plots were arranged in a 6 x 6 Latin square design and infested with second‐instar A. segetum larvae (the common cutworm). Each virus was applied in separate treatments by two application methods; as an aqueous spray containing 0.1% Agral as a wetting agent, and as a bran bait. The NPV was applied at a rate of 4 X 10¹² polyhedra/ha, and the GV at 4 X 10¹³ granules/ha. Soil and plants were sampled for larvae on three occasions following virus treatment: 24 h, 4 days and 11 days. The larvae were reared on diet in the laboratory, until death or pupation, to examine the rate and level of viral infection. Infection data showed 87.5% and 91% NPV infection and 12.5% and 55% GV infection in spray and bait treatments, respectively, in larvae sampled 24 h after treatment. In larvae sampled 4 days after treatment, the results were 78% and 100% NPV infection, and 13% and 6% GV infection. A total of only six larvae were retrieved on day 11. In both treatments larvae infected with AsNPV died significantly more rapidly and at an earlier instar than those infected with AsGV, indicating that AsNPV appears to have better potential as a control agent for A. segetum.     

The Influence of Carbon Dioxide and Daily Photon-flux Density on Optimal Leaf Nitrogen Concentration and Root: Shoot Ratio

Using a cost-benefit model, the leaf nitrogen concentrationand root : shoot ratio that maximize whole-plant relative growthrate are determined as a function of the above-ground environment(integrated daily photon flux density and the concentrationof carbon dioxide at the site of fixation within the leaf).The major advantage of this approach is that it determines theadaptive significance of leaf physiology by considering thefunctional integration of leaves and roots. The predicted responseto increasing daily photon flux densities is an increase inoptimal leaf N concentration (N_opt) and a concomitant increasein root: shoot ratio. Increased carbon dioxide concentrations,on the other hand, reduce N_opt and only slightly change root:shoot ratio. The observed increase in leaf nitrogen concentrationfound in plants growing at high altitudes (low CO₂ partial pressure)is also predicted. Since these responses to light and CO₂ maximizethe whole-plant relative growth rate, the observed adjustmentsthat plants make to light and carbon dioxide concentration appearto be adaptive. We show that the relationship between photosynthesis and leafnitrogen concentration is complex and depends on the light andCO₂ levels at which photosynthesis is measured. The shape ofthis function is important in determining N_opt and the oppositeresponse of leaf nitrogen to light and carbon dioxide is shownto be the result of the different effects of light and CO₂ onthe photosynthesis-leaf nitrogen curve. Plant growth, photosynthesis, leaf nitrogen, biomass allocation, optimization, carbon dioxide light     

Permeability to Water of the Fibre Cell Wall Material of Two Hardwoods

The permeability to water of the fibre cell wall of birch (Betulapubescens Ehrh.) and lime (Tilia x vulgaris Hayne) wood, wasmeasured in wood slices in which most of the void space wasfilled with paraffin wax or a polymerizing silicone elastomer.An osmotic technique was used with solutes of molecular weightgreat enough to prevent their molecules from penetrating thepores in the water-swollen cell wall. The solutes used weredextran and polyethylene glycol with molecular weights of 40000 and 6000 respectively. Values for permeability k x 10²¹, as defined by the Darcy equation,ranged between 3.6 m² for the tangential direction in birch,to 27 m² for the longitudinal direction in birch. These resultsare in good agreement with previously measured values but areat least ten times less than theoretical values. It is calculatedthat total emptying or filling of a wood cell through the wallmight be possible in as little as 5 min under a pressure differenceof 0.1 MPa if other flow pathways were blocked. Key words: Betula pubescens, Tilia x vulgaris, Water permeability, Fibre cell wall     

Experimental Histomoniasis in the Guinea Fowl,Numida meleagris*

Guinea fowl were inoculated rectally with Histomonas meleagridis to produce histomoniasis. The birds were infected readily by this unnatural route. Severe cecal involvement was frequent and long-lasting but liver lesions and death were rare. Turkeys given the same inoculum had high levels of liver involvement and mortality. Guinea fowl responded much less severely to infection with H. meleagridis when infected by a natural route (ingestion of a vector) rather than by rectal inoculation. Thus, naturally acquired infections with H. meleagridis appear to be of small consequence in the guinea fowl.     

Infectivity of Histomonas meleagridis of Cecal and Liver Origins Compared

SYNOPSIS. Turkey poults were inoculated rectally with 100, 1000, 10,000, or 100,000 Histomonas meleagridis from the ceca of a group of experimentally infected turkeys. Other poults were given the same numbers of histomonads from an infected liver from the same group of source birds, Comparisons of the incidence of infection, liver involvement, mortality, and average survival time following these inoculations showed that organisms of cecal origin were about 100 times more effective in producing histomoniasis than were organisms of liver origin. It is suggested that this difference in infectivity resulted from heavy losses of histomonads of liver origin that were due to various selective processes.     

A simple periphyton sampler for algal biomass estimates in streams

• 1 A simple periphyton sampler, which is cheap and easy to construct, is described. The key component is a disposable scouring disc which also serves to adsorb detached material.
• 2 Field trials show that the scouring sampler is significantly more efficient at removing and retaining periphyton from stones in streams for biomass estimation than other commonly used techniques.
• 3 The scouring sampler requires only one operator. Its small size and speed of use facilitate replication of samples. Samples can be collected from stones as small as 30mm diameter.