Interfertility of Two Mating Populations in the Gibberella Fujikuroi Species Complex

Gibberella fujikuroi and Gibberella intermedia(mating populations ‘C’ and ‘D’ of the G. fujikuroi species complex) can be distinguished by differences in the spectrum of mycotoxins produced, the lack of sexual cross-fertility and diagnostic differences in their DNA sequences. Some isolates from these two biological species, however, can interbreed and complete meiosis to produce viable progeny. Analysis of marker segregation amongst such hybrid progeny can be used to estimate the degree of genomic rearrangement and genetic incompatibility that has accumulated since these sibling species diverged. Recombinant progeny were isolated from crosses of the standard tester strains for these two species and from crosses between these standard testers and a field isolate (KSU X-10626) that was cross-fertile with tester strains of both species. Progeny in all of the crosses segregated for amplified fragment length polymorphisms (AFLPs). Segregation of AFLP loci deviated from 1:1 for two thirds of the loci amongst the progeny of the cross between the ‘C’ and ‘D’ mating population tester strains, but <20% of the polymorphic loci in the cross of either tester with KSU X-10626 showed such distortion. It was concluded that G. intermedia and G. fujikuroi are sufficiently interfertile to belong to the same biological species, but that changing the nomenclature to reflect this interfertility requires more evidence for the natural occurrence of a continuum in fertility than is presently available.     

On farm observations to increase genetic gain in breeding schemes for village poultry production – A simulation study

To improve genetic gain of breeding programs for village poultry production, breeding schemes with observations obtained in village production systems using individual (VIO) and group recording (VGO) were examined under different levels of genotype-by-environment-interactions (GxE). GxE was modeled by varying the correlation between traits measured in the breeding station and village environments for bodyweight (r_{g_BW}) and egg production (r_{g_EP}). Relative and absolute genetic gains obtained from VIO and VGO were used for comparison between the schemes. Results showed that village observations significantly improved genetic gains compared to the scheme without birds tested in the village. The improvement was only slightly larger with individual observations than with group observations. Higher r_{g_BW} and r_{g_EP} led to lower relative genetic gain, but a higher absolute gain of VIO and VGO. It is recommended to apply a breeding scheme using group recording of village performance when strong GxE in breeding for village poultry is expected.     

La Sota vaccination may not protect against virus shedding and the lesions of velogenic Newcastle disease in commercial turkeys

The aim of this project is to study the clinical signs and lesion of velogenic Newcastle disease (vND) in commercial turkeys, and also to find out if La Sota vaccination offered protection against these signs and lesions. The cockerels were included as positive controls. One hundred and twenty turkey poults and cockerels were divided into eight groups as follows: unvaccinated unchallenged turkeys (UUT), unvaccinated challenged turkeys (UCT), vaccinated unchallenged turkeys (VUT), vaccinated challenged turkeys (VCT), and along the same lines, the cockerel groups were UUC, UCC, VUC and vaccinated challenged cockerels (VCC). Vaccination was at 3 weeks of age while challenge was at 6 weeks of age. The unvaccinated turkeys and cockerels (UCT and UCC) showed different degrees of depression, diarrhoea and later paralysis at challenge. Total mortality was 100% in cockerels within 6 days, but 60% in turkeys. Similar but milder clinical signs were found in the VCC with a total mortality of 13.3%. The VCT showed mild drop in feed and water consumption, and no mortality. All the challenged groups had significant (p < 0.05) loss of weight when compared with their controls. Necropsy showed that while the UCC had severe proventricular haemorrhages, intestinal and caecal tonsil ulcers, the UCT had no digestive tract lesion. There was severe atrophy of the lymphoid organs in all the challenged groups. Histopathological sections of the bursa, spleen and thymus in all the challenged groups with special emphasis on the vaccinated and unvaccinated turkeys with mortalities of 0 and 60%, respectively, had very severe necrosis and depletion of the lymphoid tissue. Virus was isolated from the cloacal swabs. The haemagglutination inhibition antibodies were significantly higher (p < 0.05) in the challenged groups than the unchallenged. The above observations in the intestinal tracts of UCT are of diagnostic significance while the gross and microscopic lesions in the UCT and VCT show that La Sota vaccination may not protect turkeys against the destruction of the lymphoid organs by vND as earlier reported in chickens. This may lead to immunosuppression and production problems in areas where vND is enzootic.     

Evaluation of host and bacterial gene modulation during Lawsonia intracellularis infection in immunocompetent C57BL/6 mouse model

BackgroundProliferative enteritis caused by Lawsonia intracellularis undermines the economic stability of the swine industry worldwide. The development of cost-effective animal models to study the pathophysiology of the disease will help develop strategies to counter this bacterium.ObjectivesThis study focused on establishing a model of gastrointestinal (GI) infection of L. intracellularis in C57BL/6 mice to evaluate the disease progression and lesions of proliferative enteropathy (PE) in murine GI tissue.MethodsWe assessed the murine mucosal and cell-mediated immune responses generated in response to inoculation with L. intracellularis.ResultsThe mice developed characteristic lesions of the disease and shed L. intracellularis in the feces following oral inoculation with 5 × l0⁷ bacteria. An increase in L. intracellularis 16s rRNA and groEL copies in the intestine of infected mice indicated intestinal dissemination of the bacteria. The C57BL/6 mice appeared capable of modulating humoral and cell-mediated immune responses to L. intracellularis infection. Notably, the expression of genes for the vitamin B12 receptor and for secreted and membrane-bound mucins were downregulated in L. intracellularis -infected mice. Furthermore, L. intracellularis colonization of the mouse intestine was confirmed by the immunohistochemistry and western blot analyses.ConclusionsThis is the first study demonstrating the contributions of bacterial chaperonin and host nutrient genes to PE using an immunocompetent mouse model. This mouse infection model may serve as a platform from which to study L. intracellularis infection and develop potential vaccination and therapeutic strategies to treat PE.     

The utilisation of poison hoppers designed for grey squirrel (Sciurus carolinensis Gmelin) control

The grey squirrel is recognised as a pest species of economic importance but the justification of the view appears to be founded on local areas of severe damage. Despite evidence that damage may not be alleviated by squirrel population destruction, Warfarin poisoning was introduced as an alternative to trapping.The utilisation by wildlife of a poison hopper designed for grey squirrel control was investigated by automatic photography. Results confirmed that a number of species may feed from the grain presented via the hopper. However, the majority of the bait was removed during the hours of darkness when grey squirrels were not active. It is a conservative estimate that between 55 and 65% of the grain entered the environment via animals other than squirrels.In addition, the removalof bait by night visitors resulted in the accumulation of large quantities of bait at and around the entrance to the hopper tunnel. This increased accessibility to the potentially poisoned bait by animals other than squirrels.Until such time as evidence is produced to show these results as exceptional, it can only be concluded that fears expressed over the lack of specificity of this method of control are justified.     

Management of the Northern Chesapeake Bay American shad fishery

The Shad fisheries of the Chesapeake Bay in Maryland have been declining since an 1897 peak of 7860 × 10³kg. No periods of stability have been recorded. Data are presented to trace the decline not only as a function of specific areas within the Northern Chesapeake Bay but also in terms of environmental problems and recruitment overfishing.The problem is related to improving the commercial fishing yield. An estimation of a maximum effort of 200,000 man-hours is suggested if a stable yield is to be approached. Methods for obtaining this goal include alternating of closed fishing areas, adoption of rest days, enforcement of fisheries regulations and reduction of the number of metres of gill net used per fisherman.     

Europium chelate and fluorescent brightener staining of soil propagules and their photomicrographic counting—I. Methods

A method tor direct visual or photomicrographic enumeration of soil propagules in soil-agar films and soil smears, stained with a mixture ofeuropium(III) ttienoyltrifluoroacetonate and the disodium salt of 4,4¹-bis(4-anilino-6-bis(2-hydroxyethyl)amino-S-triazin-2-ylamino)2,2¹-stilbene disulphonic acid, abbreviated to Eu(TTA)₃ and fluorescent brightener (FB), respectively, is described.Soil-agar suspensions at 55–60°C were introduced into haemocytometer sample chambers of 100 μm and 20 μm depth which gave soil-agar film thicknesses of 25 μm and 12 μm, respectively, after air-drying. Soil smears air-dried on 1.25 cm² and 1.0 cm² areas of glass slide were 5.2–6.0 μm and 6.0–8.0 μm thick, respectively.The Eu(TTA)₃ is best formulated in 50% (v/v) ethanol. The best concentrations of Eu(TTA)3 and FB for staining soil propagules were 2 mM and 25 μM. respectively. A staining period of 18 h for soil-agar films and 90–120 min for soil smears was found to be optimal. The optimum volumes of 50% ethanol for rinsing soil-agar films and soil smears were found to be 12.5 and 5.0 ml. respectively.Lack of in-depth focusing on agar films 25 μm thick resulted in 15–17 per cent error in enumerations. The 12 μm agar films and soil smears required little in-depth focusing and were acceptable for photomicrographic recording of numbers of soil propagules. It is concluded that incident u.v. photomicrographic recording of soil propagule numbers in thin agar films or soil smears is a practical solution to operator fatigue likely to occur during direct microscopy.     

Fine-scale vegetation patches decline in size and cover with increasing rainfall in Australian savannas

Fine-scale vegetation patches (<5 m in width) are critically important in many landscapes because they function to obstruct surface flows of water and wind. These obstructions increase the infiltration of runoff and the capture of nutrients in runoff sediments and in wind-blown soil and litter. The importance of redistribution of runoff into runon patches from spaces between patches (fetches) is likely to be greater in drier than in wetter environments. In this paper we examine the hypothesis that the ratio of fetch to patch decreases as rainfall increases, and that this trend will be most evident on intermediate-textured soils because these soils are more prone to runoff. We measured fine-scale patches on 38 sites with sand, loam or clay soils. Sites were located along a 1000-mm rainfall gradient in the savannas of northern Australia. The width and intercept length of patches and the fetch between patches was measuring along line transects of 100–120 m oriented down slope. We found that the ratio of fetch to patch area did not decrease with decreasing rainfall, but increased on both sand and loam soils. This result was because with increasing rainfall mean spacing between patches disproportionally increased while mean patch size and cover declined. The cover of patches was negatively correlated with tree canopy cover, which significantly increased with rainfall. This negative correlation suggests that in higher rainfall savannas the size and spacing of ground-layer patches is controlled by the tree layer, and that as rainfall decreases this control decreases and runoff-runon processes increasingly structure the landscape. For savannas on clay soils these trends were not significant except that on the highest rainfall sites the cover of ground-layer patches was nearly 100% while trees were absent.