Reproductive fitness and pathogenicity of selected Radopholus populations on two banana cultivars

Ten populations of Radopholus similis from various locations and one population of Radopholus sp. from Indonesia were tested for their reproductive fitness and specific pathogenicity on Musa AAA, Cavendish cv. Poyo under controlled experimental conditions in a constant environment chamber. In addition, five of these populations were tested on Musa AAA, Ibota cv. Yangambi. Reproductive fitness of the populations tested on the two cultivars, measured as the ratio of the final number of nematodes per root system (P_f) to the number of nematodes inoculated (P_i), differed significantly. Greatest fitness was observed among R. similis populations collected from banana in different African countries (Cameroon, Uganda and the Ivory Coast) and one population from arecanut in Sri Lanka. In contrast, a population from tea in Sri Lanka and the population of Radopholus sp. from turmeric in Indonesia were the least fit. Specific pathogenicity was estimated at 8 weeks and 12 weeks after inoculation using three plant growth parameters: fresh root weight, fresh shoot weight and plant height, compared to uninfected control plants. Reduction in plant root weight was the best indicator of pathogenicity. While the R. similis populations from Uganda and the Ivory Coast were highly pathogenic, other populations with great reproductive fitness (i.e. isolates from Cameroon and Sri Lanka) did not significantly reduce root weight. In cv. Poyo, no linear correlation was found between final numbers of nematodes per gram of root (P_f) and the decrease of root weight.     

Predicting the competitive effects of weed and crop density on weed biomass, weed seed production and crop yield in wheat

Competition between winter-sown wheat and Viola arvensis Murray or Papaver rhoeas L. was studied in two experiments in two successive years. The effects of varying crop and weed density were modelled in terms of weed biomass over time, weed seed production and crop yield. Biomass model parameters, representing maximum weed biomass and intra- and interspecific competition, were obtained for different assessment dates, enabling biomass levels to be predicted during the two growing seasons. Weed biomass declined, and its maximum level was reached earlier, with increasing crop density. Intraspecific competition was higher in the absence than in the presence of crop, increasing with time and with weed density. Halving the wheat population increased June biomass of V. arvensis by 74% and of P. rhoeas by 63%. Crop yield losses with increasing weed density were greater with low than with medium and high crop populations. P. rhoeas was significantly more competitive than V. arvensis in both years. Weed biomass in 1989 responded more to reductions in crop density following the milder winter of 1988/89 than in the previous year; however crop yields were less affected in 1989 due to summer drought, restricting late weed growth and competition. Weed seed production was related to weed biomass; the progressive lowering of crop density increased seed production, and both species were very prolific in the absence of crop. By combining models, seed production could be derived for a given competitive effect on the crop. Threshold weed populations, based on low weed levels that are not economic to control, could then be equated with the accompanying weed seed production.     

The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), on insect emergence and benthic invertebrate abundance in experimental ponds

Abstract The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), predation on the production of insects emerging at the water surface and the autumn biomass of benthic macro-invertebrates were assessed in a series of experimental ponds. The study attempted to discover whether fish affect food availability for diving and dabbling ducks in freshwater habitats. Ten ponds (bisected by fine netting) were used for the study: one was left totally fish-free, whilst one half of each of three groups of three ponds was stocked with either perch, bream or perch plus bream. The relative abundance of emerging insects (mainly Chironomidae) was significantly reduced in two perch ponds, two perch + bream ponds and two bream ponds. The autumn standing crops of benthic macroinvertebrates were significantly reduced in one perch pond, three bream ponds and one perch plus bream pond. These results support findings of a contemporaneous large bio-manipulation experiment carried out in two adjacent lakes. During the biomanipulation studies, aquatic invertebrate standing stocks greatly increased after the removal of fish and decreased following restocking.     

Immunopathological aspects of canine renal disease

It is now becoming clear that the development of immunity against an infectious agent is not always beneficial to the host and may sometimes be instrumental in exacerbating the disease process. Thus, it is important to define the nature of the immunological processes which undoubtedly play an important role in some of the important renal diseases of the dog.
Deposition of immune complexes in the glomeruli stimulates a range of morphological types of glomerulonephritis. The persistence of leptospiral antigen, alone or complexed with locally produced antibody, in the renal interstitium appears to be responsible for the marked cellular response in acute leptospiral nephritis. In chronic forms of diffuse renal disease, glomerular immune complexes have been detected in chronic glomerulonephritis but not with certainty in chronic interstitial nephritis.