Frequencies and spatial patterns of white hypovirulent and pigmented strains of Cryphonectria parasitica within blight-controlled cankers on grafted American chestnut trees 15–16 years after inoculation

The frequencies and spatial patterns of white and pigmented strains of Cryphonectria parasitica were investigated within cankers in a zone on grafted American chestnut trees inoculated with white (European) and pigmented hypovirulent strains (H-inoculated zone) 15–16 years earlier. Six 7 × 7 lattice plots (each 17.8 × 17.8 cm) were established on cankers in the H-inoculated zone of the grafts. Assays of 49 bark cores per lattice indicated that 35.3% of 306 C. parasitica isolates recovered from the six lattice plots were white. The white isolates had a random pattern, potentially favorable to biocontrol, within the highly superficial cankers, based on join-count statistics of the six lattice plots. Pigmented isolates dominated the C. parasitica population, and virulence trials on American chestnut sprouts indicated 36% of the pigmented isolates from the H-inoculated zone were hypovirulent and 27% were virulent. Most (84.3%) pigmented isolates in a bark core could not be converted to the white phenotype in vitro by white isolates in the same bark core. Five of six lattice plots had a random pattern of pigmented isolates, based on join-count statistics. The sixth lattice plot was composed of an aggregate of 36 lattice cells (area = 232 cm²) containing 12 pigmented vegetative compatability (vc) groups of C. parasitica, which were interwoven in the lattice as a mosaic of thread-like forms, blocks, or ‘islands’ 32 cm² or less in area for each vc group. Hypotheses are advanced to explain why virulent pigmented strains persist in blight-controlled cankers of the H-inoculated zone but do not kill the vascular cambium.     

Edwardsiella ictaluri infection in Pangasius catfish imported from West Bengal into the Southern Caribbean

In response to a mortality event, seven Pangasius catfish (Pangasianodon hypophthalmus) were submitted to the University of the West Indies, School of Veterinary Medicine, Trinidad and Tobago, for diagnostic evaluation. These fish were part of a consignment that arrived from Kolkata two weeks earlier. Fish presented with perianal haemorrhage and blister‐like swellings on the skin which ruptured to leave ulcers. Edwardsiella ictaluri was consistently recovered from the brain and skin. Repetitive sequence‐mediated PCR analysis revealed genetic fingerprints consistent with E. ictaluri isolates from farm‐raised channel catfish in Mississippi, USA. Plasmid analysis of the case isolates identified two unique plasmids that differ slightly in conformation and content from the pEI1 and pEI2 plasmids described for E. ictaluri from other fish hosts. The case isolates were also PCR negative for several E. ictaluri virulence factors. The biological implications of these genetic differences are unclear and warrant further study. This is the first report and documentation of E. ictaluri infection in Trinidad and Tobago, suggesting the pathogen may have been introduced concurrently with the importation of fish. This report emphasizes the importance of adequate health screenings of imported lots to minimize the threat of introducing E. ictaluri to non‐endemic areas.     

Degree of Milling Effects on Rice Pasting Properties

The effects of degree of milling on pasting properties of medium‐grain (cv. Bengal and Orion) and long‐grain rice (cv. Cypress and Kaybonnet) were quantified using a Brabender ViscoAmylograph and a Rapid Visco Analyser. For all the cultivars tested, surface and total lipid contents decreased as the degree of milling increased. The peak viscosities for all rice increased with the degree of milling and the rates of increase were higher for medium‐grain than long‐grain cultivars. Degree of milling did not have a consistent effect on final viscosity for all the cultivars tested.     

Effect of osmotic potential on streptomycete growth,antibiotic production and antagonism to fungi

The growth of eighteen isolates of Streptomyces spp. on agars, the osmotic potentials of which were controlled by the addition of various solutes, showed that nine isolates were able to grow at ?100 bars and two of these grew at ?150 bars. This suggests that the water requirements of soil streptomycetes are almost as diverse as those of soil fungi. In general, linear growth and sporulation declined with decreasing osmotic potential, but one isolate grew optimally at potentials between ?5 and ?10 bars. Another isolate formed maximum amounts of a water-diffusible antibiotic per unit colony area at potentials between ?20 and ?35 bars. This appears to be the first report of osmotic potential influencing the production of antibiotic by Streptomyces. The increased antibiotic production at moderate potentials was associated with inhibition of Pythium ultimum, Rhizoctonia solani and a Curvularia sp. by the streptomycete at these potentials on osmotic agar plates. The possible ecological significance of this phenomenon in soil is discussed.     

Bacterial movement at high matric potentials—I. In artificial and natural soils

The rate of active movement of five isolates from three genera of soil bacteria in an artificial and a natural soil at high matric potentials was studied. In nutrient-amended soils the order of motility at matric potentials of —50cm and —150cm of water was: Pseudomonus fluorescens > Bacillis subtilis (two isolates) >Azotobacter vinelandii >Azotobacter chroococcum. The rate of movement of all organisms was markedly greater at the same potential in the artificial soil than in the natural soil. The faster rate in the artificial soil was attributed to the lack of a component with a high surface charge density, onto which bacteria became adsorbed. Though the influence of soil physical factors on microbial activities may be more easily studied in artificial soil systems, the lack of such a component may limit its usefulness in interpreting activities involving adsorption phenomena. Thus, while A. vinelandii moved 26mm in 48 h in the artificial soil at —50cm matric potential, there was negligible movement (5 mm in 48 h) at the same potential in the natural soil. The results indicate that, in contrast to P. fluorescens, Bacillus subtilis and Azatobacter spp. are unlikely to move appreciably through natural soil at matric potentials of less than —150cm of water.