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Methods for identifying and following microorganisms in the environment such as soils, water and plant association have been highly developed in recent years. In this study, we used rep-PCR for the characterization of Rhizobium bacteria isolated from legume trees native of Uruguay which permitted to follow them in plant inoculation assays. Among the primers used, ERIC and BOX1AR, the latter allowed the differentiation of isolates from different legumes and the finding of a high level of homology among rhizobia that nodulate the same legume species. Besides, it demonstrated that the profiles of the isolates recovered from nodules of Acacia caven, were identical to the ones used as inoculants; this confirmed the efficiency of these methods to follow these diazotrophs in the environment.

The objective of this work was to establish the experimental conditions for the production of yogurt extended with chickpea (Cicer arietinum), inoculated with St. thermophilus and L. bulgaricus and compare its chemical, microbiological and sensorial characteristics versus a yogurt made of skimmed milk. Results indicated that 70:30 and 80:20 (skimmed milk and chickpea extract) mixtures obtained by chemical score fulfilled with the proposed objectives. Yogurt made with 70:30 mixture added with modified starch (ULTRA SPERCE M and COL-FLO), did not remove syneresis present in these products and did not improve its sensory characteristics neither. Nevertheless, yogurt made with 80:20 mixture and modified starch (ULTRA SPERCE M) removed syneresis and present flavor and texture characteristics alike yogurt made of milk, this "extended" yogurt was accepted by the 80% of the judge and fulfill with yogurt specification established in the mexican regulations for this products.

The effect of specific lectin addition on Rhizobium leguminosarum-Phaseolus vulgaris symbiosis characteristics was studied. Two alternatives were selected for comparison: a) P. vulgaris seedling roots treated with lectin were inoculated with R. leguminosarum and b) P. vulgaris seedling roots were inoculated with R. leguminosarum incubated with lectin for 3 h and 72 h. The following parameters were evaluated: number and dry weight of nodules and dry matter and nitrogen content of shoot. In lectin treatments, the weight of nodules (from 13% to 35%), dry matter (from 6% to 18%) and nitrogen content (from 5% to 28%) increased significantly. The results suggest a stimulation in the formation of functional-nodules, specially in root (a) and Rhizobium (b) 72 h treatments. That is consistent with a model in which the lectin functions as an extracellular matrix component of the root interacting with roots and Rhizobium s.p. receptors.

Native strains of Rhizobium were selected from a chickpea growing area with the purpose of producing inoculants tolerant to environmental conditions of the province of Córdoba. The strains were selected for nitrogen fixing capacity and specificity with four plant genotypes using the following parameters: number of nodules, plant biomass and nitrogen content. Native population of Rhizobium spp in the province of Córdoba showed better competition ability than foreign strains with similar response to different plant genotypes.

Low productivity soils can be improved by incorporation of adapted legumes species able to increase the nitrogen fixation when associated to Rhizobium strains. Two fast-growing Rhizobium strains were isolated from nodules of Prosopis alba. Infectivity and effectivity of the strains were assessed under controlled conditions, measuring the following parameters: nodule number, dry weight, nitrogen percentage and fixed nitrogen. P. flexuosa strains showed high infective capacity (144 nodules/plant) but low effectivity (21.4 mg fixed nitrogen in 75 days). Although nodule number in P. alba was lower (23 nodules/plant) nitrogen fixation was higher (119.5 mg fixed nitrogen in 75 days) as compared with P. flexuosa. The isolated strains might be used as nitrogen donors in aride soils; they might be helpful to forestation of these ecosystems.

Nitrite production by nodules and roots of pea plants (Pisum sativum L., cultivar Alaska) inoculated with Rhizobium leguminosarum strain 3855 has been studied. Nitrate reductase (NR) activity and nitrite reductase (NiR) activity of the bacteroidal and cytosolic fractions of the nodules were also determined, as well as the nitrite content of the nodules cytosol. Nitrite production by nodules and roots from plants treated with 5 mM KNO3 was higher than that of nodules and roots from plants not treated with nitrate, and regardless of the nitrate treatment, nitrite production increased with the incubation period. The presence of nitrate, propanol or both compounds in the incubation mixtures significantly increased the nitrite production by nodules and roots. Nitrite reductase activity was detected in fresh by isolated bacteroids of R. leguminosarum strain 3855, although the presence of nitrate reductase activity could not be detected both in bacteroids of nodules isolated from plants treated or not with 5 mM KNO3. After isolation, when bacteroids were incubated in a mixture with nitrate, nitrate reductase activity developed after incubation for 12 h. Consequently, there was an increase in nitrite reductase activity, which resulted in the disappearance of the nitrite previously accumulated in the incubation medium. Nitrate utilization by bacteroids was not detected until 5 h from the beginning of the incubation period. Since the presence of chloramphenicol or rifampicin in the incubation medium prevented the development of the nitrate reductase activity, such activity was induced in bacteroids. Nitrite content and nitrate reductase and nitrite reductase activities of the cytosol from nodules of pea plants treated or not with 5 mM KNO3 varied with the buffer used for nodules homogenization. However, no nitrite was found when nodules were homogenized with ethanol, what indicates that nitrite accumulation in the cytosol occurs during the homogenization process of the nodules.

The nitrogenase activity, nitrate reductase activity and oxygen uptake as well as the hydrogen incorporation and ATP content were examined in the root nodules and bacteroids, respectively, formed by Rhizobium leguminosarum strains 128C53 (hydrogenase positive) and 300 (hydrogenase negative) in symbiosis with Pisum sativum plants grown in the presence of 2 mM KNO3. The strain 128C53 showed the greatest values for all parameters analyzed, except for the nitrate reductase activity, which was higher for the strain 300. Similarly, nodule nitrate reductase activity in strain 300 was greater than that in strain 128C53 when plants grew in the absence of combined nitrogen. In general, the highest values were obtained when determinations were made after 7 hours of plant illumination. However, the hydrogenase activity of strain 128C53 and the nitrate reductase activities of both strains increased with the light period, reaching a maximum after 14 hours of illumination. These results suggest that the benefits derived from the superior symbiotic properties and from the presence of hydrogenase activity in strain 128C53 could be counteracted by the higher rates of the nodule nitrate reductase activity in strain 300.

There is no reliable information concerning the cultivation practices of winged bean cultivars in the area; therefore, it was considered of interest to participate in the First International Winged Bean Trial, which was peformed according to a standardized procedure. The planting site was located at 90 degrees longitude and 15 degrees latitude, and 250 meters above sea level, in a hot-humid environment. Sowing was performed in the middle of November, under continuous irrigation until April. During the growth period no diseases or major pests were observed. At the initiation of harvesting in February, there were differences among varieties regarding time to reach maturity. The most promising varieties were Thailand, TPT 1, UPS 121 and Indonesia 1 with respect to seed yield. The highest protein value, 36.5%, corresponded to TPT 1, and the lowest value, 31.7% to UPS 62. Oil content in seeds of all varieties ranged from 14.0% to 19.2%. The five higher protein content varieties were analyzed for their amino acid content, and all varieties for their trypsin inhibitor activity. Leaves, roots and threshed mature pods were also analyzed for their protein content.