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George A. Stevenson

Bio: George A. Stevenson is an academic researcher. The author has contributed to research in topics: Melilotus & Taxonomy (biology). The author has an hindex of 1, co-authored 1 publications receiving 37 citations.

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TL;DR: Based on material grown, a key to the species has been developed that will be useful to agronomists and comments are made on its agronomic characteristics.
Abstract: Seed of eighteen species of sweetclover (Melilotus) from various sources in Europe and Asia has been grown at the Research Station, Brandon, Manitoba. Based on material grown, a key to the species has been developed that will be useful to agronomists. Each species is described and comments are made on its agronomic characteristics. Controversial taxa are discussed and their status is clarified.

43 citations


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TL;DR: The salt and waterlogging tolerances of 19 species of Melilotus were evaluated in a series of glasshouse experiments to identify forage species that are productive in saline environments and to identify weed risk assessments and field trials on these species.
Abstract: Identifying forage species that are productive in saline environments is an important research priority in many areas of the world affected by salinity. The salt and waterlogging tolerances of 19 species of Melilotus were evaluated in a series of glasshouse experiments. Measurements taken on each species included: dry matter (DM) production, root growth and development, shoot ion (Na+, K+ and Cl−) concentrations, root porosity, and in vitro estimates of nutritive value. Research on several species was restricted because of their potential as weed risks. Of the remaining species, M. siculus (syn. M. messanensis), an annual species, showed high relative salt and waterlogging tolerances, good DM production under non-stressed and stressed (saline and hypoxic) conditions, a high level of root porosity under stagnant conditions, low tissue ion (Na+, Cl−) concentrations, and a reasonable dry matter digestibility content (range 66–69%) under highly saline conditions. M. sulcatus ssp. segetalis and M. indicus were also identified as species with good DM production and tolerance to salinity and waterlogging stresses. Further weed risk assessments and field trials on these species are required before they can be promoted for use as pasture forages on saline areas.

86 citations

Journal ArticleDOI
TL;DR: The hypothesis that single-seeded fruits that have arisen more than once in both Medicago and Trigonella, are indeed homoplastic is supported and support for the utility of GA3ox1 sequences for phylogenetic analysis among and within closely related genera of legumes is demonstrated.
Abstract:  Premise of the study : The genus Medicago, with about 87 species, includes the model legume species M . truncatula , and a number of important forage species such as M . sativa (alfalfa), M . scutellata (snail medic), and M . lupulina (black medic). Relationships within the genus are not yet suffi ciently resolved, contributing to diffi culty in understanding the evolution of a number of distinguishing characteristics such as aneuploidy and polyploidy, life history, structure of cotyledons, and number of seeds per fruit.  Methods : Phylogenetic relationships of 70 – 73 species of Medicago and its sister genus Trigonella (including Melilotus ) were reconstructed from nucleotide sequences of the plastid trnK/matK region and the nuclear-encoded GA3ox1 gene (gibberellin 3- β -hydroxylase) using maximum parsimony and Bayesian inference methods.  Key results : Our results support certain currently recognized taxonomic groups, e.g., sect. Medicago (with M . sativa ) and sect. Buceras . However, other strongly supported clades — the “ reduced subsection Leptospireae clade” that includes M . lupulina , the “ polymorpha clade ” that includes M . murex and M . polymorpha and the “ subsection Pachyspireae clade ” that includes M . truncatula — each of which includes species presently in different subsections of sect. Spirocarpos , contradict the current classifi cation.  Conclusions : These results support the hypothesis that some characters considered important in existing taxonomies, for example, single-seeded fruits that have arisen more than once in both Medicago and Trigonella , are indeed homoplastic. Others, such as the 2 n = 14 chromosome number, have also arisen independently within the genus. In addition, we demonstrate support for the utility of GA3ox1 sequences for phylogenetic analysis among and within closely related genera of legumes.

79 citations

Journal ArticleDOI
01 Mar 1976-Nature
TL;DR: The first successful application of phytoalexin induction as a tool in taxonomic studies to the problems of classification at the generic and species level in the Leguminosae is reported.
Abstract: IT is well established that many higher plants respond to microbial invasion by the de novo production of organic substances called phytoalexins1,2. These compounds are absent from healthy plants and are induced by the attacking microorganisms. Although the role of phytoalexins in disease resistance is not yet entirely clear, considerable evidence suggests that they are of importance in the protection of higher plants from fungal colonisation. Although few surveys have been attempted, there is clearly a taxonomic element in phytoalexin biosynthesis, in that different plant families accumulate chemically different types of compounds3. Thus, the Leguminosae in general produce isoflavonoids, the Solanaceae diterpenes, the Compositae polyacetylenes and so on2; anomalies are rare, for example, the furanoacetylene, wyerone acid, from Vicia faba (Leguminosae)4. As lesser variations also occur within these families, there is the clear possibility of using phytoalexin induction as a tool in taxonomic studies. We report here the first successful application of this technique to the problems of classification at the generic and species level in the Leguminosae.

63 citations

Journal ArticleDOI
TL;DR: It is proposed that salinity measurements to determine annual legume suitability for winter-dominant rainfall areas are made in summer or early autumn, when at their highest levels.
Abstract: Herbage production and persistence of 42 annual pasture legumes from 33 species were measured at five sites across southern Australia. Medicago polymorpha L. was highly productive on soils, particularly those not prone to waterlogging, with soil surface (0–10 cm soil depth) salinity [estimated by electrical conductivity (ECe)] levels in summer of up to 36 dS/m, whereas M. truncatula Gaertn. was productive on ECe levels of at least 11 dS/m. Trifolium michelianum Savi and T. resupinatum L. were highly productive on soils subject to waterlogging, but only where 0–10 cm summer ECe levels were less than 8 dS/m. No commercial species were adapted to highly saline (0–10 cm summer ECe levels >8 dS/m), waterlogged sites. However, Melilotus siculus (Turra) Vitman ex B.D. Jacks. has the potential to fulfil this role, provided an appropriate Rhizobium strain can be selected. Mixtures of species and cultivars should be sown to account for high spatial variability for salinity and waterlogging. Traits for annual legume success in saline landscapes include salinity and waterlogging tolerance in germinating seedlings and mature plants, early flowering, hardseededness and delayed softening of hard seeds. Establishment of regenerating seedlings is associated with the timing of hardseed softening in relation to rainfall events capable of leaching topsoil salts. It is proposed that salinity measurements to determine annual legume suitability for winter-dominant rainfall areas are made in summer or early autumn, when at their highest levels. Transects along salinity and waterlogging gradients are suggested as an alternative method to traditional plots for genotype evaluation.

46 citations