Intraspecific metabolic diversity among strains ofBurkholderia cepacia isolated from decayed onions,soils, and the clinical environment

A collection of 218 strains ofBurkholderia cepacia (including 18% strain replicates) was assembled from organic soils, decayed onions, and clinical sources. Each strain was characterized for virulence to onion, catabolic ability using the Biolog GN microtiter plate, and several other behaviors. Overall test reproducibility was estimated at 98%. The results obtained using the Biolog GN system corresponded well to those obtained using standard methods. Three coefficients of resemblance (Gower similarity, pattern difference, and Jaccard similarity) were calculated and clustered by the group-average method. The sorted matrices and phenograms, while giving evidence of an underlying phenetic structure to theB. cepacia nomenspecies, gave little evidence of sorting by broad source of isolation. Strains isolated from within fields or samples were frequently found to be similar, however, strains isolated from fields with similar cropping histories were not. The Gower-transformed centroids of ordained clusters were projected in a principal coordinate system and estimates of disjunction were calculated. Strains ofB. cepacia were shown to be non-uniformly distributed in taxonomic space. Strains isolated by serial dilution on onion slices formed a tight phenetic cluster which includes the type strain of the nomenspecies and that of a synonymous group (Pseudomonas multivorans); the strains in this phenon were generally virulent to onion and were partially differentiated from others by pectolytic behavior and by the production of diffusible pigment on King's medium A. Further characterization should better resolve the taxonomy of the nomenspecies.     

Interactions between mycorrhiza and powdery mildew of cucumber

Interactions between the arbuscular mycorrhizal fungus Glomus intraradices and the powdery mildew fungus Podosphaera xanthii were examined with cucumber as the host plant in pot experiments under greenhouse conditions. Plants were inoculated with mildew two weeks after seedling emergence. Plants were mycorrhizal or not, prior to mildew infection and were harvested two weeks after mildew inoculation. We found no influence of the cucumber — G. intraradices symbiosis on development of cucumber mildew in terms of numbers of colonies per unit area. Similarly, biomass and amount of energy reserves of G. intraradices as examined with signature fatty acids were unaffected by mildew. Both biotrophs caused growth depressions of the host plant. Plant carbon allocation is discussed in relation to biotrophs as sinks.     

Commentary: Moving From Practice to Research,and Back

It is a widely accepted idea that knowledge from research needs to be better integrated into practice. Considerable energy is dedicated to strengthening the flow of research to practice. Less attention, however, has been paid to strengthening the ways researchers can learn from practice to improve their work. In this commentary, we draw on our work over the past decade to offer reflections on the nature and pace of practice, the gaps between practitioners’ needs and available research, and the importance of trust and relationships. Although there are no easy responses to these challenges, we can create a dialogue about them and begin to work collectively toward overcoming them.