The efficiency of 13 phosphate-solubilizing bacteria (PSB; four Burkholderia sp., five Enterobacter sp., and four Bradyrhizobium sp.) was assessed in a soil plate assay by evaluating soil phosphorus (P) availability. A commercial argentine strain, Pseudomonas fluorescens, was used for comparing solubilizing activity. Burkholderia sp. PER2F, Enterobacter sp. PER3G, and Bradyrhizobium sp. PER2H strains solubilized the largest quantities of P in the soil plate assay after 60 days as compared with the other strains, including the commercial one. The effect of PSB inoculation on growth and nutrient uptake of soybean plants was also studied under greenhouse conditions. Plants inoculated with Burkholderia sp. PER2F had the highest aerial height and showed an appropriate N/P ratio. However, none of the PSB increased P uptake by plants. This suggests that PSB inoculation does not necessarily improve P nutrition in soybean, nor was there any relationship between P availability in the soil plate assay and P content in the soybean shoot in the greenhouse. We concluded that the selection of efficient PSB strains as possible inoculation tools for P-deficient soils should focus on the integral interpretation of soil assays, greenhouse experiments, and field trials.

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Asparagus is a highly perishable product owing to its high respiratory rate, a reason why modified atmosphere packaging (MAP) has been used in order to increase the shelf-life of fresh asparagus. Carotenoid and chlorophyll pigments are important compounds for the maintenance of both the nutritional and sensory quality of asparagus. In this study, green asparagus spears were stored under refrigeration at 2 • C for 14 days, under MAP at 2 • C for 26-33 days and under MAP at 10 • C for 20 days. Pigment profiles were determined using high-performance liquid chromatography (HPLC), with three classes of compounds being detected, namely oxygenated carotenoids (xanthophylls), hydrocarbonated carotenoids (carotenes) and chlorophylls. The xanthophylls identified were neoxanthin, violaxanthin, lutein and zeaxanthin. Only β-carotene was detected in the carotene fraction. In the chlorophyll pigments, three molecules were isolated, chlorophyll b, its epimer chlorophyll b and chlorophyll a. Also detected were the first degradation products of chlorophylls, pheophytins b and a respectively. Modified atmosphere packaging at 2 • C was found to be effective in extending the shelf-life for up to 4 weeks and in preserving the colour of fresh asparagus.

Two hundred and fifty strains, all of them representatives of native Bradyrhizobium sp., isolated from soils cultivated with soybean have been characterized by their denitrification activity. In addition, the denitrification potential of those soils was also measured by evaluating the most-probable-number (MPN) of denitrifying bacteria and the denitrification enzyme assay (DEA). Of the 250 isolates tested, 73 were scored as probable denitrifiers by a preliminary screening method. Only 41 were considered denitrifiers because they produced gas bubbles in Durham tubes, cultures reached an absorbance of more than 0.1 and NO 3-and NO 2-were not present. Ten of these 41 were selected to confirm denitrification and to study denitrification genes. According to N 2 O production and cell protein concentration with NO 3-, the isolates could be differentiated in three categories of denitrifiers. The presence of the napA, nirK, norC and nosZ genes was detected by production of a diagnostic PCR product using specific primers. RFLP from the 16S-23S rDNA spacer region (IGS) revealed that denitrifiers strains could be characterized as Bradyrhizobium japonicum and strains which were nonrespiratory denitrifiers as B. elkanii.

Bacterial populations were surveyed on phylloplane of field‐grown soybean every 20 days in south‐ern Buenos Aires, Argentina. The crop was disease‐free and no pesticides were applied. Out of 523 bacterial isolates (mainly Gram positive bacteria) from upper and lower leaves, 134 of them were Bacillus spp. Bacillus pumilus was the dominant species followed by Bacillus subtilis. The proportion of Bacillus spp. decreased from 80% of all bacterial isolates in early stages to 0% at harvest, whereas the diversity of Bacillus spp. decreased from nine species at day 45, to one species at day 133, shortly before harvest. Among the isolates, a significant increase in the percentage of nitrifiers with plant aging was observed on lower and upper trifoliates. In contrast, proteolytic bacteria were more abun‐dant on lower than on upper trifoliates at all sampling dates. The consistent recovery of B. pumilus from soybean phylloplane during most of the crop cycle indicated this species as an inter‐esting candidate for future plant microbial management and biocontrol studies.