Size distribution and chemical composition of marine aerosols: A compilation and review

Some 30 years of physical and chemical marine aerosol data are reviewed to derive global-size distribution parameters and inorganic particle composition on a coarse 15°×15° grid. There are large gaps in geographical and seasonal coverage and chemical and physical aerosol characterisation. About 28% of the grid cells contain physical data while there are compositional data in some 60% of the cells. The size distribution data were parametrized in terms of 2 submicrometer log-normal distributions. The sparseness of the data did not allow zonal differentiation of the distributions. By segregating the chemical data according to the major aerosol sources, sea salt, dimethylsulfide, crustal material, combustion processes and other anthropogenic sources, much information on mass concentrations and contribution of natural and anthropogenic sources to the marine aerosol can be gleaned from the data base. There are significant meridional differences in the contributions of the different sources to the marine aerosol. Very clearly, we see though that the global marine surface atmosphere is polluted by anthropogenic sulfur. Only in the case of sulfur components did the coverage allow the presentation of very coarse seasonal distributions which reflect the spring blooms in the appropriate parts of the oceans. As an example of the potential value in comparing the marine aerosol data base to chemical transport models, global seasonal meridional MSA distributions were compared to modelled MSA distributions. The general good agreement in mass concentrations is encouraging while some latitudinal discrepancies warrant further investigations covering other aerosol components such as black carbon and metals

Influence of growth factors on the plant pathogens by select suppression of Pseudomonads

Non-Peer ReviewedRhizobacteria were evaluated for their ability to inhibit the growth of damping-off pathogens such as Pythium ultimum, Rhizoctonia solani and common root rot pathogen, Cochliobolus sativus. The level of antagonism by Pseudomonads 63-28, U-14 and Ral-3 was examined on solid growth media under varying conditions of temperature, pH, and sources of C, N, and amino acids. In vitro antibiosis of the pathogens was greatly influenced by environmental and nutritional conditions. Generally, antagonism was greatest at 25-300C and decreased at 400 C. The influence of pH appears to be rhizobacteria and pathogen dependent. For example, optimum inhibition of P. ultimum growth by 63-28 was between pH 4.6-6.0, whereas, optimum inhibition of R. solani growth by U-14 was at 7.6-9.1. Growth inhibition of C. sativus by Ral-3 was pH independent. Mannitol or trehalose strongly enhanced the antifungal activity of 63-28, whereas lactose had a negative effect. Antagonism of 63-28, U-14 and Ral-3 was enhanced by nitrogen sources tested except NaNO2 on U-14. The influence of the amino acids did not effect Ral-3, but, antibiosis by 63-28 was increased by amino acids phenylalanine, arginine, or histidine. U-14's activity was increased with the addition of proline, serine, or arginine. The results from this study clearly show that growth factors have a significant impact on microbial antagonism

Rhizobacterial influence on healthy stand establishment of canola grown in Rhizoctonia solani infested fields of Saskatchewan

Non-Peer ReviewedPre-emergence seedling damping-off, seedling blight, and brown girdling root rot caused by R. solani are important diseases of canola/rape seed in western Canada. Annual yield losses in excess of 20-30% have been reported in several infected fields. Cultural control methods or resistant cultivars are currently unavailable for these diseases. Chemical fungicides have been developed for use to control the disease, but the success rate has been varied. However, the use of chemicals is becoming less acceptable from an environmental point of view. Several studies indicated that biological control using plant growth promoting rhizobacteria may also be effective in controlling R. solani. Field plots were established in Saskatoon, Regina and Melfort, SK, in 1990, 1991 and 1992 to evaluate the potential of rhizobacterial strains as seed treatments to increase the healthy stand of canola CV. Westar grown in R. solani infested field. The bacteria were formulated either in sterile peat or in a liquid carrier and applied to seed just before planting. Bacterized seed were mechanically planted in replicated field plots artificially infested with R. solani. Final healthy stand was measured 30 days after planting. Grain yields were determined by harvesting the plots. Seed bacterization significantly increased the final healthy stand compared to non-bacterized controls. Strains which increased stand showed in vitro antagonistic activity to not only R. solani but also other pathogens such as Pythium ultimum, Fusarium solani and F. oxysporum. Some of these strains induced root elongation of canola under laboratory conditions. Rhizosphere colonization, chemical compatibility and shelf-life of the important bacteria will be discussed

Influence of storage conditions on the shelf-life of microbial inoculants and their biocontrol activity towards damping-off pathogens

Non-Peer ReviewedSelect microbial inoculants (Ral-3, 64-3, 63-28, and G8-32) were produced in proprietary liquid formulation, placed into commercial packages and stored at different temperature regimes. Shelflife of bacteria and level of antagonism were evaluated against the damping-off pathogens Pythium paracondrium, Rhizoctonia solani, Fusarium solani, and Cylindrocarpon destructans when retreived from the commercial packages after storage. Although differing in their antibiosis mechanisms, strains Ral-3 and 63-28 were significantly consistent in their antagonistic activity towards the fungi tested, irrespective of their storage conditions. Strains 64-3 and G8-32 did differ in their activity against the fungi. The storage temperature of 40°C affected the shelf-life of 64-3 by reducing it to Log 4.3 cfu/ml and the antagonistic activity of G8-32 was low against R. solani at all temperatures. However, the storage temperature of -20°C did not affect the activity or shelf-life of the strains