Antagonistic Pythium against pathogenic Pythium on cucumber roots1

Antagonistic microorganisms introduced into the growing medium, the seed or the root, have been shown to reduce the attack of many soil-borne plant pathogenic fungi. In 1983, three experiments with Pythium oligandrum were carried out using cucumber seedlings artificially inoculated with Pythium splendens. The seedlings cv. Ideal Nova were grown in shallow boxes containing granulated rockwool fibre (Grodania). The plants were grown at a minimum temperature of 20°C in a glasshouse. Plants were treated with the antagonist either by coating the seeds, or by applying a disc of a PDA-culture to 9-day old seedlings. The pathogen was introduced 9 or 5 days later, respectively, by adding PDA culture discs to the rockwool; 15 and 38 days later, the area with attacked roots was calculated as a percentage of the box-bottom area. The experiments showed that it is possible to control P. splendens by either method of application. P. oligandrum was able to colonize the seed and rhizosphere and suppress P. splendens for at least 38 days. If future experiments are similarly positive, the methods for use in commercial horticulture should be worked out as soon as possible.     

THE KINETICS OF HETEROGENEOUS ISOTOPIC EXCHANGE

Isotopic exchange of phosphate ions between soil and solution was examined with particular emphasis on the slower reaction involving the incorporation of the tracer in the solid phase that follows the very fast exchange reaction between the solution and the surface of solid. Experimental data fitted both an equation composed of a sum of exponentials and a much simpler two-constant equation. The goodness of fit was similar in each case but it was concluded that the exponential type of equation was not useful as a means of elucidating the mechanisms involved. The two-constant equation may be derived from the kinetics of crystallization and recrystallization processes, and therefore provides an interpretation which is amenable to experimental verification.     

Comparison of chemical, electrophoretic and in vitro digestion methods for predicting fish meal nutritive quality

Chemical, electrophoretic and in vitro digestion methods were compared with respect to predictions given regarding fish meal (FM) quality. FMs were manufactured by mixing a press-cake, with spray dried stickwater concentrate from the identical raw material, thereby providing samples containing different quantities of water-soluble protein (wsp). A low-temperature-dried FM was employed as a reference. Acquired chemical data for each of the FMs included amino acid analysis and proximal composition (protein, fat, ash, ammonia, titration, salt, moisture). Biological methods in rat (net protein utilization, NPU, biological value, BV, and true digestibility, TD), capillary electrophoresis (sodium dodecyl sulphate-capillary gel electrophoresis, SDS-CGE)) and an in vitro enzymatic assay (trinitrobenzene sulphonic acid-based closed system with rainbow trout enzyme extract) were used for further comparisons with FM wsp content. A high correlation ( R  = 0.97; P  < 0.001) between FM wsp content and titration volume was observed. In contrast to BV and NPU ( R  = 0.98; P  < 0.001), TD ( R  = 0.2; P  = 0.63) did not correlate with FM wsp. The peak area of a 50 kDa signal derived from SDS-CGE showed significant correlation ( R  = 0.98; P  < 0.001) with wsp content. The fish-based in vitro system provided correlations with wsp content with respect to predigestion ( R  = 0.97; P  < 0.0001) and post digestion ( R  = 0.77; P  < 0.03) and for enzymatic liberation of amino groups as post digestion minus predigestion ( R  = 0.97; P  < 0.0001) from the FM examined.     

AGEING OF PHOSPHATE ADDED TO SOIL

The ageing of phosphate added to suspensions of a calcareous soil was measured in terms of the solubility of the phosphate and the amount of isotopically exchangeable phosphate (E value). These both showed a decrease in reactivity of the added phosphate during a period of 5 months. A constant ratio of E values after 24 and 500 hours showed that no redistribution within different fractions of labile phosphate occurred.     

Vibrio anguillarum serovars associated with vibriosis in fish

Abstract. A total of 517 Vibrio anguillarum strains isolated from discased fish together with 14 V. anguillarum serogroup O2 and V. ordalii type strains were serotyped using the European scrotyping system. Marked species differences were recorded. In isolates from salmonids serovar O1 (70.2%) and O2 (20.2%) were dominantwhilst a minor proportion belonged to other serogroups or were non-typeable. Figures for turbot were similar to those from salmonids. In 32 isolates from sea bass, sea bream and mullet, most strains belonged to serogroup O1. while one was O2a. one O7, and the rest non-typeable In cod serovar O2 was dominant while only a minor proportion belonged to other serogroups or were non-typeable. The ecl isolates belonged equally to serovars O2 and O3. All O2 strain were subtyped with absorbed O2a and O2b antisera. O2a was dominant in all fish species. but in cod. the relative number of O2b isolates was considerably higher than in other fish species. The applicability of the European serotyping system is discussed and compared with other serotyping systems.