Reduction of lignin levels in the forage legume alfalfa (Medicago sativa) by down-regulation of the monolignol biosynthetic enzyme hydroxycinnamoyl coenzyme A:shikimate hydroxycinnamoyl transferase (HCT) results in strongly increased digestibility and processing ability of lignocellulose. However, these modifications are often also associated with dwarfing and other changes in plant growth. Given the importance of nitrogen fixation for legume growth, we evaluated the impact of constitutively targeted lignin modification on the belowground organs (roots and nodules) of alfalfa plants. HCT downregulated alfalfa plants exhibit a striking reduction in root growth accompanied by an unexpected increase in nodule numbers when grown in the greenhouse or in the field. This phenotype is associated with increased levels of gibberellins and certain flavonoid compounds in roots. Although HCT down-regulation reduced biomass yields in both the greenhouse and field experiments, the impact on the allocation of nitrogen to shoots or roots was minimal. It is unlikely, therefore, that the altered growth phenotype of reduced-lignin alfalfa is a direct result of changes in nodulation or nitrogen fixation efficiency. Furthermore, HCT down-regulation has no measurable effect on carbon allocation to roots in either greenhouse or 3-year field trials.

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Kentucky bluegrass {Poa pratensis L.) is a widely used, high-quality, sod-producing turfgrass. To maintain an acceptable level of quality and function requires irrigation in the semiarid regions of the western United States. Landscape water use, however, is coming under increased scrutiny, and reducing water inputs is a goal of many municipalities. To identify Poa germplasm that maintains green color under deficit irrigation over summer seasons, this study was designed to evaluate the percent of green cover of 24 Kentucky bluegrass cultivars, accessions (including core collections), and other Poa species. Cultivars generally had a higher percent green cover in spring and fall, while several accessions and old U.S. cuitivars showed higher green cover during summer months. Other Poa species did not have percent green cover values above any cultivars and as a group consistently performed the lowest. Core collections of Kentucky bluegrass, aimed at representing overall variability of the species with fewer accessions, had variance estimates equal to or higher than the overall group of accessions. Seven cultivars and accessions consistently had higher percent green cover than the Midnight cultivar check during the August data collection dates, highlighting the potential to improve Kentucky bluegrass green cover over summer seasons under deficit irrigation.

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Few North American legumes are available for rangeland revegetation in the semiarid western United States. Western prairie clover (Dalea ornata [Douglas ex Hook.] Eaton & J. Wright) is a perennial legume with desirable forage characteristics and is distributed in the northern Great Basin, Snake River Basin, and southern Columbia Plateau. Understanding the genetic and ecotypic variability of this species is a prerequisite for developing populations suitable for revegetation purposes. To address this need, we established two common-garden plots of western prairie clover from 22 sites in Idaho, Oregon, and Washington. Significant variation was detected among the collections for all traits measured. Among the measured traits, flowering date was correlated with collection-site temperature and elevation. Population structure estimates from 474 amplified-fragment length polymorphism markers resulted in two distinct, genetically differentiated groups and a third admixed group, and flowering date played a significant role in discriminating those genetic-based groupings of collections. Positive correlations were observed between phenotypic and genetic distance matrices (r 5 0.33, P 5 0.005), phenotypic and geographic distance matrices (r 5 0.35, P 5 0.002), and genetic and geographic distance matrices (r 5 0.31, P 5 0.009). Based on these results, we recommend that two germplasm sources of western prairie clover be developed for use across the collection area, one from the Deschutes River region and the other encompassing Idaho, Washington, and eastern Oregon collection sites. Resumen Existen pocas leguminosas disponibles en los Estados Unidos de Norteamérica para la revegetación en las zonas semiáridas del oeste Estados Unidos. El trébol de la pradera occidental (Dalea ornata [Douglas ex Hook.] Eaton & J. Wright) es una leguminosa perene con características de un forraje deseable y se distribuye en el norte de la cuenca del Snake River, y en la meseta Columbia en el noroeste de los Estados Unidos. La comprensión de la variabilidad gene´tica y ecotípica de esta especie es un requisito para el desarrollo de las poblaciones adecuadas para fines de revegetación. Para enfrentar esta necesidad, establecimos dos parcelas de jardín común de tre´bol de pradera occidental provenientes de 22 sitios de Idaho, Oregón, y Washington. Se detectó una variación significativa entre las colecciones para todos los rasgos medidos. Entre los rasgos medidos, la fecha de floración se correlacionó con la temperatura del sitio de la colección y la elevación. La estructura de la población se estimó de 474 marcadores de polimorfismo de la longitud del fragmento amplificado resultaron en dos grupos distintos genéticamente diferenciados y un tercer grupo mezclado. La fecha de floración desempeñ ó un papel importante en separar esas agrupaciones basándose en las colecciones gene´ticas. Se observaron correlaciones positivas entre los fenotipos y las matrices de distancia genética (r 5 0.33, P 5 0.005), fenotipo y las matrices de distancias geográficas (r...