Taxonomy of the infraspecific variability of cultivated plants

Summary The needs and aims of taxonomy of cultivated plants at the infraspecific level are dealt with briefly in the context of taxonomy in general. The components of infraspecific taxonomy of cultivated plants are formulated and defined. These components are: identification, classification, genealogy, nomenclature — that are complementary to each other. The desired requirements of each component are discussed in the light of a review, conducted for this paper, on the subject covering the period (1975-) 1976–1979.Developing automatic identification schemes for cultivars is becoming increasingly important. Identification needs to be accurate, rapid and devoid of human error. A classification system must be based on as many characters as possible and use numerical taxonomic techniques to generate and evaluate groupings. A suitable system would be composed of polythetic, non-hierarchical, informal groupings. The most useful genealogies are those that trace individual pedigrees as far back as possible. They can most profitably be done with the aid of computer systems, such as those used for oat and barley cultivars, by the author and his associates. Because there is no one to one correspondence between genealogies and classifications, pedigrees or genealogies enable one to draw inferences about cultivars different from those drawn from classifications. A nomenclature system for cultivars must be as complete as possible. This is achieved by listing all the cultivars names, commercial synonyms, translations and transliterations, and cross referencing. Examples of confusions due to faulty nomenclature are provided. In the author's opinion, a nomenclature system for cultivar groups is not needed because it is too cumbersome and because groups need not be formalized.It is desirable to work on the four components of infraspecific taxonomy at a world-wide basis to increase their usefulness for growers, merchants, breeders and scientists concerned with cultivar development and improvement. An exception might be in identification within a country whereby a local system might satisfy most current needs.

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Taxonomie der infraspezifischen Variabilität von Kulturpflanzen

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New method for a two-step hydrolysis and chromatographic analysis of pectin neutral sugar chains

A new method for the determination of the main neutral sugars in pectin has been developed. The sample preparation involves a mild chemical attack followed by an enzymatic hydrolysis. The completeness and nondestructive character of the method are demonstrated by comparison of the results obtained with different acids such as H2SO4, HCl, and trifluoroacetic acid (TFA) at different concentrations (2, 1, or 0.2 M) at two temperatures (80 or 100 degrees C). The chemical hydrolysis of pectin neutral sugar chains with strong acid (1 or 2 M) and high temperature (100 degrees C) shows that the liberation of the pectin sugars is not realized at the same rate for each sugar. Different optimum conditions are thus obtained. However, the chemical pectin hydrolysis with 0.2 M TFA at 80 degrees C is characterized by the liberation of pectin neutral sugar side chains without any degradation within 72 h of hydrolysis. Under these conditions, the liberation of some pectin sugars, essentially galactose, glucose, and rhamnose, was not complete. An enzymatic hydrolysis is necessary to obtain a complete release of all the sugars. The combination of the two treatments, a chemical hydrolysis realized with diluted acid (0.2 M) for 72 h at low temperature (80 degrees C) on one hand and an enzymatic hydrolysis on the other hand, allow a total liberation of pectin sugars. The quantitative analysis of the carbohydrates is realized with accuracy, high selectivity, and sensitivity with high-performance anion-exchange chromatography with pulsed-amperometric detection. The sugars can be analyzed without any derivatization with a limit of quantification of 0.1 mM.     

Vertical porosity profile of a clay-rich marsh soil

The evolution of clay soil porosity is currently demonstrated via the shrinkage curves in a large water content domain spreading from a shrinkage limit to a liquidity limit. In fact, the parallel between in situ profiles and the shrinkage curves in such a large water content range is difficult to obtain because of the lack of earth pressure in the laboratory tests and in situ limited water contents. The vertical distribution of porosity throughout a clay-rich marsh soil profile was studied in a grassland field with samples taken from the soil surface characterized by water contents near their shrinkage limit down to 2.00 m deep saturated sediments over their liquidity limit. The depth of the plasticity limit isolates a soil in a solid state characterized by a vertical prism-like structure from a plastic to pseudo-liquid state in depth. The porosity was calculated from the measurements of the density of intact samples by double weighing and image analysis of 100 cm² polished sections. The initial structure of clay soil was maintained by impregnation based on water–acetone–resin exchange. An ultraviolet photo luminescent pigment added to the resin allowed the capture of images from which shrinkage cracks and microporosity of the clay matrix were easily separated. The distribution of porosity between the shrinkage crack mesoporosity and the clay matrix microporosity was evaluated after the mathematical decomposition of the grey level curves characteristic of each level. Vertical evolution of the porosity distribution from the soil surface in a solid state to the plastic and pseudo-liquid sediment in depth was presented on the shrinkage curve of the clay material. The measurements point out how the clay matrix microporosity and mesoporosity of shrinkage cracks are complementary and the role of the scale effect on the shrinkage curve. The analysis of images captured on an optical microscope under polarized and analyzed light and the SEM observation of freeze-dried samples demonstrated the isotropic arrangement of the clay particles in typical “honey-comb” architecture in the in situ plastic-to-liquid saturated domain. Eventually the distribution of porosity through the profile results from the evolution of the initial “honey-comb” microstructure of the sediment induced by the desiccation phenomenon. It is governed by the depth of plasticity limit of the clay material and by the depth of the water table.