The practice of inoculating forage legumes with rhizobia strains is widespread. It is assumed that the inoculated strain determines the performance of the symbiosis and nitrogen fixation rates. ...However, native-naturalized strains can be competitive, and actual nodule occupancy is often scarcely investigated. In consequence, failures in establishment, and low productivity attributed to poor performance of the inoculant may merely reflect the absence of the inoculated strain in the nodules. This study lays out a strategy followed for selecting a
sv. trifolii strain for white clover (
) with competitive nodule occupancy. First, the competitiveness of native-naturalized rhizobia strains selected for their efficiency to fix N
in clover and tagged with
A was evaluated in controlled conditions with different soils. Second, three of these experimental strains with superior nodule occupancy plus the currently recommended commercial inoculant, an introduced strain, were tested in the field in 2 years and at two sites. Plant establishment, herbage productivity, fixation of atmospheric N
(
N natural abundance), and nodule occupancy (ERIC-PCR genomic fingerprinting) were measured. In both years and sites, nodule occupancy of the native-naturalized experimental strains was either higher or similar to that of the commercial inoculant in both primary and secondary roots. The difference was even greater in stolon roots nodules, where nodule occupancy of the native-naturalized experimental strains was at least five times greater. The amount of N fixed per unit plant mass was consistently higher with native-naturalized experimental strains, although the proportion of N derived from atmospheric fixation was similar for all strains. Plant establishment and herbage production, as well as clover contribution in oversown native grasslands, were either similar or higher in white clover inoculated with the native-naturalized experimental strains. These results support the use of our implemented strategy for developing a competitive inoculant from native-naturalized strains.
Ergot disease (Claviceps paspali) and sterility have the potential to reduce seed yield in bahiagrass (Paspalum notatum Flüggé). Our objective was to determine the genotypic and environmental effects ...on seed yield, and the levels of ergot and sterility. Seventeen genotypes were evaluated in three locations across two years for seed yield, ergot severity, and total seed fractions (percentage of full seeds, ergot sclerotia and empty seeds). The percentage of full seeds and total seed yield were correlated (r = 0.52) but both were negatively correlated with the percentage of ergot sclerotia (r = −0.81 and −0.51). Empty seeds were negatively correlated with full seeds (r = −0.39), but not with ergot sclerotia and total seed yield. The genotype effect was significant for total seed yield and severity of infection with large heritabilities (H2 = 0.92 and 0.86) but had no effect on the percentage of the seed fractions. Location and the interaction with genotype explained most of the variation in the percentage of the seed fractions and their weight. Ergot and sterility were significant detrimental factors, genotype was a major determinant of ergot levels and seed yield, while non-genetic factors were co-determinants in constructing the seed yield potential but were the main determinants of the yield potential realization.
El Uruguay forma parte de los Pastizales del Río de la Plata, una de las áreas más extensas de pastizal en el mundo, con una biodiversidad destacada. Actualmente, la presión derivada de la ...intensificación en el uso del suelo determina que estos ecosistemas se encuentren deteriorados. A nivel productivo, una práctica usual es sembrar leguminosas exóticas en cobertura, con fertilización fosforada, sobre pastizal natural. El objetivo de este trabajo fue evaluar el impacto de niveles crecientes de fertilización sobre la riqueza de especies vegetales, la presencia de exóticas y la productividad primaria neta. También se revisaron posibles mecanismos que expliquen los cambios observados en la diversidad. Se establecieron dos sitios experimentales: PA, en las Sierras del Este, y GL, en la Cuesta Basáltica. Se dispuso de ocho tratamientos con niveles variables de fertilización fosforada en parcelas sembradas con Lotus angustissimus. Se calculó la productividad primaria neta total y de L. angustissimus (PPNAt y PPNALa) para los primeros tres años del experimento. Además, se realizó un muestreo florístico al tercer año y medio, en el que se evaluó la riqueza de especies vegetales (total y de exóticas). La riqueza total disminuyó con la fertilización y la riqueza de exóticas aumentó. La PPNAt y la PPNALa aumentaron con la fertilización en PA, pero no en GL. Para PA no es posible afirmar qué mecanismos actúan detrás de la pérdida de especies, mientras que en GL es posible que entren en juego mecanismos de las hipótesis de ‘dimensionamiento del nicho’ y de ‘competencia total’. Concluimos que se debe estudiar más esta tecnología en búsqueda de estrategias de fertilización que logren mejoras en la productividad sin comprometer la biodiversidad.
High stocking rate livestock management has determined the decline of native species of high forage value as Bromus auleticus Trin ex Nees in the Campos region of the Rio de la Plata grasslands. The ...species has some agronomic and ecological characteristics that define it as of high potential to be reintroduced in degraded natural grasslands. However, Bromus auleticus has not been sufficiently described, since commercial seeds and information regarding the establishment phase are scarce. Two field experiments were carried out in 2013 and 2014, reintroducing Bromus auleticus into native grasslands in the Basaltic region, aiming to evaluate the impact of sowing density in the forage productivity and their seasonal distribution. The treatments consisted of different sowing densities: 20, 40, 60 and 80 kg ha-1 and one control treatment. Considering the management and the evaluated period (4 years for experiments 2013, and 3 years for experiments 2014), different sowing densities did not modify the forage production in any of the plantings for the evaluated period and compared to the control. However, the use of sowing densities of 40 kg ha-1 or higher allowed modifying the seasonal distribution of forage production with a better contribution in autumn-winter, and more stable production throughout the year.
Sorghum dried distillers’ grain with soluble (S-DDGS) has not been utilized as supplement in lamb growing and finishing diets under grazing conditions in summer. The hypothesis was that the ...performance of post-weaning lambs grazing Paspalum notatum (PN) INIA Sepé supplemented with an energy-protein diet (whole sorghum grain SG, and soybean meal SM) is not reduced by the inclusion of 40% S-DDGS. During 82 days, in summer, 42 Merino Dohne male lambs (130 ± 7.6 days of age, 32 ± 2.4 kg of body weight BW, and 2.2 ± 0.2 body condition score BCS) were evaluated, in a completely random experimental design with three treatments and two replicates each (n = 14 each one). All lambs grazed PN INIA Sepé and in two treatments they were daily supplemented (1.7% BW) with different components. The treatments were: PN (control group, no supplementation), SGSM (70% SG, 30% SM) and DDGS (45% SG, 40% S-DDGS, and 15% SM). Supplemented lambs had higher (P<0.0001) body weight gain (BWG), final BW and wool growth (140 and 126 g/a/d, 43.5 and 42.4 kg; 1814 and 1892 µg/cm2/d for DDGS and SGSM, respectively) than control lambs (40 g/a/d; 35.5 kg; 1353 µg/cm2/d) (P<0.0001), without differences between supplemented groups. Gastrointestinal nematodes infestation (GIN) was affected by the treatments on day 69, where supplemented animals showed lower infestation levels than control lambs (P=0.0024). The inclusion of S-DDGS in the supplement did not reduce the productive performance of the lambs when the concentration of crude protein and energy remained constant.
El grano de destilería seco con solubles de sorgo (DDGS-S) no se ha utilizado como suplemento en dietas de engorde de corderos bajo pastoreo en verano. La hipótesis planteada es que el desempeño de corderos posdestete pastoreando Paspalum notatum (PN) INIA Sepé y suplementados con una ración energético-proteica (grano entero de sorgo y harina de soja) no se reduce con la inclusión de un 40% de DDGS-S. El diseño experimental fue completamente al azar con tres tratamientos y dos repeticiones cada uno (n = 14 cada uno), evaluando 42 corderos machos Merino Dohne (130 ± 7,6 días de edad, 32 ± 2,4 kg de peso vivo PV, y 2,2 ± 0,2 de condición corporal CC) en verano (84 días). Todos los corderos pastorearon PN INIA Sepé, dos tratamientos fueron suplementados diariamente (1,7% PV). Los tratamientos fueron: PN (sin suplementación), SGSM (70% grano sorgo, 30% harina de soja) y DDGS (45% grano sorgo, 40% DDGS-S y 15% harina de soja). Los corderos suplementados tuvieron mayor (P<0,0001) ganancia de peso, peso final y crecimiento de lana (140 y 126 g/a/d; 43,5 y 42,4 kg; 1814 y 1892 µg/cm2/d para DDGS y SGSM, respectivamente) que los corderos control (40 g/a/d; 35,5 kg; 1353 µg/cm2/d) (P<0,0001), sin diferencias entre los suplementados. La infestación por nemátodos gastrointestinales fue afectada por los tratamientos en el día 69, los animales suplementados mostraron menores niveles de infestación que los corderos control (P=0.0024). La inclusión de DDGS-S en el suplemento no redujo el desempeño productivo de los corderos cuando la concentración de proteína cruda y la energía permanecieron constantes.
Grãos de destilaria desidratados de sorgo com solúveis (DDGS-S) não têm sido utilizados como suplemento em dietas de crescimento e terminação de cordeiros em condições de pastejo no verão. Postulamos que o desempenho de cordeiros pós-desmame em Paspalum notatum (PN) INIA Sepé suplementado com uma ração energético-protéica (grão de sorgo e farelo de soja) não é reduzido pela inclusão de 40 % DDGS-S. Em um delineamento experimental inteiramente casualizado com três tratamentos e duas repetições cada (n = 14 cada um), avaliamos 42 cordeiros Merino Dohne (130 ± 7,6 dias de idade, 32 ± 2,4 kg de peso corporal -PC- e 2,2 ± 0,2 escore de condição corporal) no verão (84 dias). Todos os cordeiros foram alimentados com PN INIA Sepé e dois tratamentos suplementados diariamente (1,7 % do PC). Os tratamentos foram: PN (sem suplementação); SGSM (70 % grão de sorgo, 30 % farelo de soja) e DDGS (45 % grão de sorgo, 40 % DDGS-S e 15 % farelo de soja). Cordeiros suplementados tiveram maior (P<0.0001) ganho de peso corporal, peso corporal final e crescimento de lã (140 e 126 g/a/d; 43,5 e 42,4 kg; 1814 e 1892 µg/cm2/d para DDGS e SGSM, respectivamente) do que cordeiros controle (40 g/a/d; 35,5 kg; 1353 µg/cm2/d) (P<0.0001), sem diferenças entre os suplementados. A infestação por nematóides gastrointestinais foi afetada pelos tratamentos no dia 69, animais suplementados tiveram uma infestação menor do que os cordeiros controle (P=0.0024). A inclusão de DDGS-S no suplemento não reduziu o desempenho produtivo dos cordeiros quando a concentração de proteína bruta e energia desta permaneceu constante.
Ensifer (syn. Sinorhizobium) meliloti U143 is an effective nitrogen-fixing strain isolated from Uruguayan soils. For decades, this strain has been used as an inoculant for different alfalfa ...cultivars. Here we report for the first time a characterization of the U143 elite strain that includes the preliminary genomic sequence, its annotation, and physiological parameters related to its symbiotic efficiency and nitrate respiration capacity. Through Illumina sequencing, the genome of the U143 strain was sequenced. The genome length was 6,801,966 bp, and it contained two megaplasmids, an average GC content of 62.15 %, and 6522 protein-coding sequences. In the symbiotic plasmid, we identified nap, nir, nor, and nos sequences that explain the ability of the U143 strain to respire NO3- in free-living and microaerobic conditions. Field assays performed in two locations for two years showed that alfalfa inoculated with the U143 strain produced 41 % more total shoot dry matter than the non-inoculated control, and between 61.3 % and 66.5 % of shoot N in alfalfa inoculated with strain U143 derived from nitrogen fixation.
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•Ensifer meliloti U143 strain was isolated from Medicago sativa nodules in Uruguayan soils. .•Elite U143 strain has been used as a commercial inoculant for alfalfa cultivars since 1991.•The genome length was 6,807,606 bp, with a GC average content of 62.14 % and 6522 protein-coding sequences.
Six species of Trifolium (T. polymorphum Poir., T. riograndense Burkart, T. argentinense Speg., T. medium L., T. pratense L. and T. repens L.) were analyzed using inter-simple sequence repeats (ISSR) ...markers. Six selected primers generated 186 polymerase chain reaction (PCR) products exploring 112 loci in 34 genotypes analyzed with molecular sizes ranging from 200 to 1300 bp. These primers were able to discriminate among and within species, with the PCR products being on average 41.6% species-specific and 59.9% polymorphic at the within species level. Nuclear DNA content was determined by flow cytometry and revealed variation among species. The 1Cx genome size values were calculated and were found to range from 0.46 pg (T. pratense) to 0.96 pg (T. polymorphum). Genome size values of South American species were higher than those of Eurasiatic origin. The analyses of the molecular data grouped the six species in agreement with their geographical origin and clearly differentiate T. polymorphum from T. argentinense. The Eurasiatic group showed the highest average of species-specific bands (45.3%) and the South American group exhibited the highest amount of total bands (59.7). The highest level of intra-species polymorphisms was detected in T. argentinense (92.9%), followed by T. medium (89.5%).
Aluminum (Al) toxicity in acid soils is one of the factors limiting crop production. Alfalfa (Medicago sativa L.) is the most important forage legume worldwide and is susceptible to Al toxicity. Our ...objective was to identify genomic regions associated with Al tolerance in tetraploid alfalfa. A segregating population obtained from a cross between Altet‐4 (Al‐tolerant genotype) and NECS‐141 (Al‐sensitive genotype) was evaluated for Al tolerance using a callus bioassay and a whole plant assay in media and genotyped using molecular markers. Phenotyping results for both callus and root growth assays exhibited a normal distribution and patterns of transgressive segregation. The linkage maps covered 761 cM for Altet‐4 and 721 cM for NECS‐141. Markers associated with Al tolerance from both assays were detected using single‐factor analysis. Quantitative trait loci (QTL) for Al tolerance were identified on linkage groups (LGs) 1, 4, and 7 using interval mapping, and these QTL explained 20.8, 15.2, and 21.7% of the variation, respectively. A second population was used to evaluate the identified Al tolerance QTL in a different genetic background. Although mechanisms of Al tolerance in tetraploid alfalfa are quantitative, the identification of relevant genomic regions and candidate genes involved in abiotic stress responses can facilitate the selection of desirable alleles to accelerate the development of alfalfa cultivars that can be productive in acid and Al‐toxic soils.
Reliable phenotypic assays are essential to identify genetic variation for factors limiting crop productivity. Aluminum in the soil is highly phytotoxic and is a major limitation to crop production. ...Current methods to evaluate Al tolerance in alfalfa (Medicago sativa L.) based on root characteristics are time consuming, labor intensive, and subject to microenvironmental variation. Our objective was to develop two rapid whole-plant assays, one in culture media and one in soil, to evaluate acid and Al tolerance in alfalfa. The culture-media method involved measuring root growth and architecture 2 wk after growing the plants in media at pH 7.0 without Al, pH 4.0 without Al, and pH 4.0 with Al. The greenhouse-based soil method is simpler, faster, and more efficient than previously used soil assays. The two assays produced similar results, consistently distinguishing between Al-sensitive and Al-tolerant alfalfa genotypes in accord with previously described assays. These whole-plant assay methods will enable the screening of breeding populations to improve Al tolerance and the dissection of the genetic determinants underlying variation in tolerance responses.
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