Tolerance ofRhizobium leguminosarum bv.phaseoli to acidity and drought

Ten strains ofRhizobium leguminosarum bv.phaseoli isolated from soils of Morocco were more tolerant than three culture collection strains to acid conditions in culture media or in sterile soil. The survival rate of a tolerant strain in a sandy acid soil was greater than a sensitive strain at different humidity levels. These properties should give locally selected strains an advantage in nodulatingPhaseolus vulgaris roots in soils similar to those used here.     

Use of a novel plasmid to monitor the fate of a genetically engineered Pseudomonas putida strain

Plasmid pSI30 was constructed to increase the sensitivity of detection of a genetically engineered micro-organism (GEM) and its recombinant DNA in environmental samples. This broad host-range, mobilizable plasmid contained chlorocatechol (clc) degradative genes, antibiotic resistance genes (ampicillin and kanamycin) and a fragment of eukaryotic DNA. The clc genes encode enzymes that convert 3-chlorocatechol to maleylacetic acid permitting the host, Pseudomonas putida RC-4, to grow on 3-chlorobenzoate. This catabolic phenotype was exploited using enrichment procedures to detect RC-4(pSI30) cells, free-living in the water column or when irreversibly bound to surfaces. The eukaryotic DNA sequence provided a unique target allowing positive identification by DNA:DNA hybridization. Using the eukaryotic DNA sequence as a probe, no transfer of the plasmid to indigenous bacteria was detected. Persistence of RC-4(pSI30) and its ability to multiply upon addition of 3-chlorobenzoate were demonstrated 78 days after its addition to natural freshwater. In flow-through microcosms RC-4(pSI30), undetectable as free-living cells, was found by enrichment as irreversibly bound sessile forms. These experiments revealed the stability of pSI30 and its utility in a 'combination' detection system for tracking the survival of a GEM and its DNA in environmental samples.     

Survival and development of Pieris brassicae larvae upon application of sublethal doses of chlordimeform

Larvae of the large cabbage white butterfly, Pieris brassicae L. are important pests of cruciferous crops. Third and fifth instars were treated topically with sublethal doses of the formamidine pesticide chlordimeform. A number of excitable actions were induced but they did not persist beyond 24 hours. Following the initial period, however, subsequent development was delayed and mortality increased, particularly when third instars were treated. Dosing fifth-instar larvae caused few further deaths. A link is suggested between these results and the nutritional status of the insects, and they are discussed in terms of how they might contribute towards control.

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Résumé Les chenilles de troisième et cinquième stades de P. brassicae L. ont reçu une application superficielle de chlordiméforme, insecticide à la formamidine. Les doses inférieures à 335 g/g ont été sublétales, provoquant plusieurs formes d'excitation. Bien que leur comportement soit redevenu normal en 24 heures, les troisièmes stades traités ont eu leur développement retardé et une mortalité accrue. Le traitement des chenilles plus âgées a eu moins d'effets. Une relation est suggérée entre ces observations et le régime alimentaire de cet insecte; une réduction de l'alimentation, plus importante chez les chenilles de troisième que de cinquième stade de P. brassicae, accompagne le début des altérations du comportement provoquées par le chlordiméforme. La discussion porte sur le mécanisme de contrôle sublétal du chlordiméforme, impliquant des effects immédiats et retardés.

     

Growth,maturation and survival in a laboratory-reared Rhabdocoelid Turbellarian,Macrostomum orthostylum (BRAUN 1885)

Growth, maturation and survival of a free living turbellarian Macrostomum orthostylum (BRAUN), from a brackish water fish-farm, were studied in the laboratory under a constant temperature of 24 °C. The worms tolerated a wide range of salinity (1 to 30‰). Maximum growth (total length) of 1000 μm was attained in 56 days with a mean growth rate of 15.7 μm d^-1. Minimum maturation time (7 days) and highest longevity (112 days) were recorded in 9%. salinity. Survival period was considerably longer at lower salinities (1 to 10‰) and showed negative relationship with higher salinities (11 to 30‰).     

Effects of gravel size and peat material concentrations on embryo survival and alevin emergence of brown trout,Salmo trutta L.

Embryo survival and alevin emergence pattern of brown trout were studied in simulated redds with different homogeneous gravel sizes and different concentrations of peat material. Optimal survival (95%) occurred in 18 mm gravel and survival decreased with decreasing gravel size. High concentrations (40%) of peat material resulted in low survival (65%). The proportion of premature emerging alevins increased in finer gravels and at high peat concentrations. Premature alevins had a large yolk sac and are probably very vulnerable to predators.     

Factors affecting the survival of E. coli in a river

The relationships between physical, chemical and microbial characteristics of an aquatic ecosystem and the survival of E. coli have been studied. Two conditions of the ecosystem (warm and cold) are considered. T₉₀ (time necessary for 90% of a bacterial population to die) in the warm situation shows an inverse exponential relationship with water temperature. Besides the direct relationship temperature-T₉₀, there is an indirect effect of temperature upon T₉₀ through the natural microflora of the water. The relationships between temperature and the heterotrophic population, and between the heterotrophic population and the bacterial consumers (P.F.U.), are exponential and linear, respectively.     

Experimental observations on the transmission of Schistosoma margrebowiei miracidia

Evans N. A. 1985. Experimental observations on the transmission of Schistosoma margrebowiei miracidia. International Journal for Parasitology15: 361–364. The survival and infectivity characteristics of Schistosoma margrebowiei miracidia at a temperature of 26°C are described. The maximum survival time and the time to 50% survival were approx. 13 and 9.5 h respectively. Miracidial infectivity toward Bulinus natalensis was relatively constant for the first 4 h of life but it then declined steadily to zero after 11–12 h. Snails exhibited age-dependent differences in their susceptibility to infection, individuals being most susceptible when 4 days old. Increases in snail age beyond 1 week were generally accompanied by an increased level of resistance to infection. Exposure of neonate (< 2 days old) snails produced high levels of mortality and a very low proportion of the survivors were infected at the time of parasitological examination.     

Influence of Meloidogyne hapla on Alfalfa Yield and Host Population Dynamics

Self-thinning in alfalfa, a dynamic process involving the progressive elimination of the weakest plants, was enhanced by Meloidogyne hapla. Alfalfa stand densities decreased exponentially with time and were reduced 62% (P = 0.05) in the presence of M. hapla. As stand densities decreased over time, mean plant weights increased at a rate 2.59 times faster in the absence of M. hapla. In a stepwise multiple regression analysis, 65% of the total variation in yield could be explained by changes in stand density and 85% by average weight of individual stems. Alfalfa yields were suppressed (P = 0.05) by M. hapla, with suppression generally increasing with time and as the nematode population density increased. Yield suppression was attributable primarily to the decline in plant numbers and to suppression in individual plant weights.     

Distribution,biology and hybridization of Scaphirhynchus albus and S. platorynchus in the Missouri and Mississippi rivers

Synopsis Scaphirhynchus albus and S. platorynchus were studied in Missouri during 1978–1979 to assess their distribution and abundance, to obtain information on their life histories, and to identify existing or potential threats to their survival. S. platorynchus was collected in substantial numbers (4355 specimens) at all 12 sampling stations in the Missouri and Mississippi rivers, while only 11 S. albus were captured from 6 stations. Twelve specimens identified in the field as hybrids between the two species were captured from 4 stations. Morphometric and meristic comparisons of presumed hybrids with the parent species, using cluster and principal components analyses, demonstrated intermediacy of most specimens identified in the field as hybrids. Aquatic insects comprised most of the diet of S. platorynchus and S. albus, but S. albus and the hybrids had consumed considerable quantities of fish. S. albus grew more rapidly than S. platorynchus, while the growth of hybrids was intermediate. Hybridization appears to be a recent phenomenon, resulting from man-caused changes in the big-river environment. Hybridization may be a threat to survival of S. albus in the study streams.     

Temperature control of germination and its possible role in the survival of a non-dormant population of Avena fatua

Germination of freshly harvested seeds of a non-dormant (ND) line (Stonehouse 319) of wild oats ( Avena fatua L.) was inhibited by incubation of the seeds at relatively high temperatures of 25 and 30°C. The germination inhibition in these seeds appeared to be a case of thermo-inhibition which was the direct effect of hightemperature treatment (HIT), since it did not persist after transferring the seeds to an optimum germination temperature of 20°C. Even a prolonged HTT of 30°C for over 5 weeks did not prevent germination of about 80% of the seeds transferred to 20°C. However, in a significant proportion of the seeds, thermo-dormancy was induced by 10 days of HTT at 30°C if the seeds were then incubated at sub-optimal temperatures of 5 to 15°C. This thermo-dormancy would appear to be 'restrictive' in form, since its expression was restricted to very specific conditions. Relatively low inclubation temperaturs of 5 and 10°C markedly slowed germination whether HTT was applied or not. The results suggest that thermo-inhibition and thermo-dormancy, induced during seasonal temperature fluctuations, may provide a survival mechanism for seeds of such ND lines as Stonehouse 319.