Pheno-genotypic and symbiotic characterization of isolated rhizobia of Desmanthus Virgatus (l.) Willd. In soils of the province of Jujuy (Argentina)

Las leguminosas forrajeras nativas presentan un gran potencial productivo y un ejemplo de ellas es Desmanthus virgatus de amplia distribución en el centro norte de Argentina. El objetivo del trabajo fue realizar una caracterización feno-genotípica y simbiótica de rizobios que forman nódulos en D. virgatus con vista hacia el uso sustentable integral de dicha leguminosa. Para ello, se estableció una colección de 17 aislamientos recuperados de suelos de Jujuy. La caracterización fenotípica permitió reconocer rizobios de crecimiento rápido que mostraron un desarrollo óptimo entre pH 5 y 8, temperaturas de 28 a 35°C, y en concentraciones de 1% (p/v) de NaCl. Se hallaron rizobios con capacidad de crecimiento en condiciones extremas de pH 9 y a 40°C. Los aislamientos se identificaron como pertenecientes a Ensifer spp. y los perfiles de amplificación de ADN genómico mostraron escasa diversidad genética. La inoculación de D. virgatus con la cepa 8L12.1 (Ensifer sp.) produjo incrementos de biomasa seca aérea de 73% en cámara de cultivo y 124% a campo respecto a las plantas sin inocular y sin fertilizar.Native forage legumes have great productive potential and an example of which is Desmanthus virgatus with a wide distribution in central and northern Argentina. The objective of the work was to carry out a pheno-genotypic and symbiotic characterization of rhizobia that form nodules in D. virgatus with a view to the integral sustainable use of said legume. For this, a collection of 17 isolates recovered from Jujuy soils was established. Phenotypic characterization allowed to recognize fast-growing rhizobia that showed an optimal development between pH 5 y 8, temperatures to 28 a 35°C, and in concentrations of 1% (w/v) of NaCl. Rhizobia with growth capacity were found under extreme conditions of pH 9 and at 40°C. The isolates were identified as belonging to Ensifer spp. and the genomic DNA amplification profiles showed little genetic diversity. The inoculation of D. virgatus with the strain 8L12.1 (Ensifer sp.) produced increases of 73% aerial dry biomass in the cultivation chamber and 124% in the field with respect to the uninoculated and unfertilized plants.Instituto de Biotecnologia y Biologia Molecula

FR 27. Milk production: responses to high temperature

Milk production, fat and protein contents during last summer are analyzed in the Units of Intensive Milk Production at Rafaela Experimental Station, in Santa Fe, Argentina. Milk production presented an inverse relationship with maximum temperature (P<.01) while percentage of protein decreased as a function of minimum temperature (P<.05). Fat contents also decreased with increasing temperature, the relationship not being statistically significant. When considering a heat wave during December, during which maximum temperature reached 37.9 ºC, these responses were even more significant. Daily milk production per cow after the heat wave was 3.0 L lower than it was before this highly stressing period. It is concluded that temperatures as high as those recorded during the heat wave would not allow for a recovery of milk production; and that protein contents would be more sensitive to the lack of night recovery of the lactating animals