Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    The paramo vegetation of Ramal de Guaramacal, Trujillo State, Venezuela. 1. Zonal communities
    Cuello, A.N.L. ; Cleef, A.M. - \ 2009
    Phytocoenologia 39 (2009)3. - ISSN 0340-269X - p. 295 - 329.
    high tropical andes - plant-communities - life-forms - superparamo - cordillera - patterns - gradient - poaceae - merida - growth
    Zonal paramo vegetation communities present on top of Ramal de Guaramacal, Trujillo state, Venezuela, have been studied with the aim to provide a syntaxonomic scheme or classification, based oil analysis of the physiognomy, floristic composition, ecological relations and spatial distribution of the different vegetation communities. A total of 91 vascular species, 33 species of bryophytes and 11 species of lichens have been documented from fifty 10 m-line intercept transects, each surveying 10 in of altitudinal interval oil zonal paramo vegetation present between 2800 and 3100m altitude. The interpretation of the TWINSPAN clustering allowed the recognition of five vegetation communities at association level grouped into two alliances and one order. Three associations of lower subparamo or shrubby paramo and two of upper subparamo or bunchgrass paramo dominated by rosettes and tussock plants have been documented. The alliance Hyperico paramitanum-Hesperomeletion obtusifoliae groups the shrubby paramo associations: Ruilopezio paltonioides-Neurolepidetum glomeratae and Disterigmo acuminatum-Arcytophylletum nitidum, present on wind protected slopes, dwarf forests edges or along streams. The alliance Hyperico cardonae-Xyridion acutifoliae groups one widely distributed shrubby parama, association Cortaderio hapalotrichae-Hypericetum juniperium and two open grass paramo associations: Puyo aristeguietae-Ruilopezietum lopez-palacii and Rhynchosporo gollmeri-Ruilopezietum jabonensis, present on wind exposed slopes. Asteraceae and Ericaceae are the most speciose of families, followed by Poaceae and Cyperaceae. The most diverse genera are Ruilopezia (Asteraceae), Rhynchospora (Cyperaceae) and Hypericum (Clusiaceae). Diversity of species and growth forms is greater among the shrubby communities, decreasing in the bunch grass-rosette communities. Canonical correspondence analysis (CCA) indicates that floristic composition of zonal vegetation communities is mostly related to slope angle and altitude than to other observed variables such as pH, soil depth and humus depth. The generic and species composition is that of a rain bamboo paramo.
    Cereals and pulses of Tropical Africa. Conclusions and recommendations based on PROTA 1: 'Cereals and pulses'.
    Bosch, C.H. ; Borus, D.J. - \ 2007
    Wageningen : PROTA Foundation - 96
    graansoorten - peulvruchten - poaceae - fabaceae - taxonomie - plantengeografie - teelt - plantenvermeerdering - tropisch afrika - cereals - grain legumes - poaceae - fabaceae - taxonomy - phytogeography - cultivation - propagation - tropical africa
    Measuring the yield gap : technische mogelijkheden voor verbetering van graslandproductiviteit
    Meuleman, J. ; Schut, A.G.T. ; Smits, M.C.J. - \ 2006
    Wageningen : Plant Research International (Nota / Plant Research International 416) - 36
    poaceae - lolium perenne - gewasproductie - gewasopbrengst - productiemogelijkheden - graslanden - nederland - poaceae - lolium perenne - crop production - crop yield - production possibilities - grasslands - netherlands
    Toepassing Moddus in graszaadgewassen, zaadoogst 2002 en verwerking over jaren
    Borm, G.E.L. ; Kassies, J. ; Wever, A.C. - \ 2004
    Lelystad : Praktijkonderzoek Plant & Omgeving B.V. - 33
    grassen - poaceae - zaden - plantengroeiregulatoren - groeiregulatoren - zaadproductie - graszaden - akkerbouw - grasses - poaceae - seeds - plant growth regulators - growth regulators - seed production - grass seeds - arable farming
    In 2002 werd onderzoek uitgevoerd naar het optimale toepassingstijdstip van Moddus in zaadgewassen bestemd voor de eerste en tweede zaadoogst van Engels raaigras, veldbeemdgras en roodzwenkgras. Een toepassing (0,8 L Moddus per ha) op het aanbevolen tijdstip voor raaigrassen werd vergeleken met een laat toepassingstijdstip en een zeer laat toepassingstijdstip
    Kweek is infectiebron van DTR in tarwe
    Kastelein, P. ; Köhl, J. - \ 2003
    Boerderij/Akkerbouw 88 (2003)11. - ISSN 0169-0116 - p. 14 - 15.
    tarwe - graansoorten - schimmelziekten - pyrenophora tritici-repentis - waardplanten - gastheer parasiet relaties - overwintering - rotaties - agropyron - poaceae - wheat - cereals - fungal diseases - host plants - host parasite relationships - rotations
    Kweek blijkt een waardplant vor de schimmel Pyrenophora trici-repentis die op deze plant ook kan overwinteren. Bij de bestrijding van de gele bladvlekkenziekte speelt het bouwplan een rol, de ziekte wordt vaker aangetroffen bij tarwe als voorvrucht dan bij een andere voorvrucht
    Reconciling scientific approaches for organic farming research
    Baars, T. - \ 2002
    Wageningen University. Promotor(en): L. 't Mannetje; N.G. Röling; A. Elgersma. - Driebergen etc. : Louis Bolk Institute [etc.] - ISBN 9789058087713 - 345
    biologische landbouw - landbouwkundig onderzoek - methodologie - experimenteel veldonderzoek - filosofie - trifolium repens - weidevlinderbloemigen - poaceae - grassen - planteninteractie - dierlijke meststoffen - plantenplagen - bodembiologie - plantenparasitaire nematoden - aardwormen - kalium - nederland - biologisch-dynamische landbouw - wetenschap - organic farming - agricultural research - methodology - field experimentation - philosophy - trifolium repens - pasture legumes - poaceae - grasses - plant interaction - animal manures - plant pests - soil biology - plant parasitic nematodes - earthworms - potassium - netherlands - biodynamic farming - science

    Part I : Reflection on research methods in organic grassland and animal production at the Louis Bolk Institute, The Netherlands

    Key words: organic agriculture, anthroposophy, methodology, research strategy, experiential science, multidisciplinary science, Goethean science

    This dissertation focuses on the research question: what is peculiar to agricultural research when its purpose is to support the conscious development of organic agriculture? What approaches, designs and methods are used for such research? Since the 1990s the Louis Bolk Institute has become one of the important actors in the field of organic research and development. The author analysed the methodological aspects of seven case studies, each following the same format: background of the project, methods used, a reflection on the methods and, to a limited extent, agronomic results. Each of these sheds light on an aspect of the Louis Bolk Institute's approach to research.

    Organic farming is experienced as a new paradigm and its research methods need to do justice to it. Three criteria were formulated for this purpose: the self regulation of farming systems, the involvement of farmers and the respect for the integrity of life. Two conceptual frameworks are used to analyse the research methods: (1) a four-quadrant matrix. Epistemological, ontological and methodological changes in the way of thinking are relevant in discussions about holism versus reductionism and positivism versus constructivism. The second framework is (2) a triangle which can show the relationship between the underlying values, the involvement of the actors and the nature of the scientific process.

    The scientific position which is defended in this dissertation can ultimately best be described as a 'radical holistic research strategy'.

    Research approaches applied in the case studies are: interdisciplinary research, experiential science and mutual learning, farmer-to-farmer learning, exploring tacit knowledge, bio-ethical evaluation, Goethean science and systemic development. In the four quadrant matrix two new additional research methods are positioned: (1) Goethean science is included as a holistic counterpart to multidisciplinary system ecology; (2) experiential science is included for comparison with mono-disciplinary experimental research. The constructivist character of both Goethean science and experiential science particularly distinguishes these methods from mainstream science.

    The meta-reflection on the research showed some important new elements of research. There was a systemic orientation in terms of a cohesive set of management measures and actions. This systemic orientation also encompasses holism in terms of Goethean science. In addition there is the experiential science based on intuitive action and pattern recognition. The reflection on the methods made it clear that their acceptance was influenced by the underlying scientific philosophy.

    The entire research strategy is thus based on two different interpretations of knowledge. Experiential science focuses on the actions of the farmer and is based on the epistemology of action. In addition there is an epistemology of knowledge, where it relates to interdisciplinary research and Goethean science. There are barriers to the acceptance of these scientific methods in the current lack of suitable statistical evaluation methods, and also in the absence of accepted methods for explicitly exploring reality as constructed by people.


    Part II : Effects of manure types and white clover (Trifolium repens) cultivars on the productivity of grass-clover mixtures grown on a humid sandy soil

    Key words: organic agriculture, grass-clover, white clover cultivars, animal manure, potassium, nematodes, earthworms

    This Part describes the agronomic results of the multidisciplinary grassland study. This project concerned the effects of clover varieties and spring applications of animal manure on the yield of grass-white clover mixtures on a moist sandy soil (1993-1996). To be aware of the context of the findings in a multidisciplinary approach, attention was paid to: chemical soil fertility, damage to clover by slugs and soil borne nematodes. To increase the understanding of soil fertility, earthworm dynamics were also measured. At the end of the period the botanical composition of all plots was assessed. Factors measured besides total yield and clover yield were N, P and K yield. It was found that these 'context'- measurements were important for the overall explanation of the scientific results. Data were used for modelling several relationships between yield parameters. The overall findings of this project led to an understanding and description of the main aspects of manure with regard to grass-white clover growth on a moist sandy soil.

    It was concluded that on a moist sandy soil the amount of inorganic and organic N, the N release and the K input were the main manure factors relating to fluctuations in total yields on white clover development and on N yields in the first six years after sward establishment. The inorganic N component in manure can be used strategically to improve the growth of the herbage in spring. Maintenance of soil fertility in terms of P, K and Ca levels is an important key factor for a successful organic grass-clover sward.

    Carbon rich FYM derived from a deep litter stable and composted before application increased the earthworm population, reduced the number of nematodes and maintained the highest level of soil pH, all factors which might positively affect white clover growth in the long term. FYM applied in spring resulted in the typical extended growth season in the second part of the growing season. On a sandy soil the high concentration of K in the FYM positively affects the potential white clover growth.

    The choice of a persistent white clover cultivar is another important factor affecting herbage and N yields of an organic grass-clover sward. However, winter losses were not found to be the main cause of white clover reductions over the years. Losses in the growing season were related to slugs which reduced white clover leaf area. The literature shows that the cyanide concentration in DM herbage affects the susceptibility of white clover to pests.
    Apomixis in Brachiaria decumbens Stapf
    Dusi, D.M.A. - \ 2001
    Wageningen University. Promotor(en): M.T.M. Willemse. - S.l. : S.n. - ISBN 9789058083579 - 167
    urochloa decumbens - poaceae - apomixis - koolhydraatmetabolisme - moleculaire genetica - genexpressie - urochloa decumbens - poaceae - apomixis - carbohydrate metabolism - molecular genetics - gene expression

    Apomixis is asexual reproduction leading to a seed. It is the predominant mode of reproduction in grasses of the genus Brachiaria.

    Brachiaria decumbens is one of the widely cultivated species of grasses in the tropical areas. The knowledge about the mechanisms of apomixis and the possibility of controlling this system will extend the possibilities of introducing variability in Brachiaria and will maintain the apomictic character desirable for its propagation.

    A comparison of gametophyte development between a sexual diploid (D4) and an apomictic tetraploid (D58) genotype of Brachiaria decumbens was made.

    A calendar made based on the development in time show the differences between sexual and apomictic development. The aposporic embryo sac of the Panicum type grows faster than the Polygonum meiotic one. The apospore initials in Brachiaria decumbens were observed very early in the ovule, next to archespore or to the meiocyte. During microspore and ovule development, the pattern of callose deposition was different in sexual and apomictic plants.The distribution of the nuclei, positioned in one pole in the aposporic embryo sac allowed to differentiate them from the bipolar distribution of the nuclei observed in meiotic embryo sacs of the sexual plants. Cellularisation took place early in aposporic embryo sac and by the time of anthesis embryogenesis had already started in the apomict. In ovules of apomictic plants many embryo sacs developed. Apomixis expressed in the female side, had also an influence on the male side.

    Histochemical tests developed to localise the in situ sucrose synthase or invertase activity were used during ovule development in an apomictic and a sexual genotype of Brachiaria decumbens . A delay of activity of both enzymes was observed in apomictic compared to the sexual development. This delay was also reflected by the amount of carbohydrates detected in a HPLC assay. Furthermore antibodies were used to localise the enzyme in the cell. The higher level of carbohydrates detected in the early stages of development in the sexual plant is in line with the amount of enzyme and its activity. The retarded metabolism of carbohydrate in the apomict could be related to the entrance of the apospore directly in gametophytic pathway leading to a faster embryo sac development.

    Total mRNA pattern as observed by labelling poly A tails did not detect the differences in expression in sexual and apomictic plant ovules. But the difference found in the in situ amount of total RNA showed a change in metabolism of cells that are differentiating from nucellar cells in the chalazal side of the archespore or meiocyte during aposporic development. Such cells the first initial apospores also showed ribosome population that differ from other nucellar cells. In the sexual plant, the presence of some particular cells in the nucellus at chalazal side of the meiocyte suggested a silent aposporic capacity of this tissue. If such cells could develop into apospore initials under other conditions, like polyploidisation, is not known. In our observations the diploid plants never developed apospores in any stage of ovule development. Only studies with artificial polyploids could give a clue to these questions.

    Differential display of mRNA was used for identifying and cloning differentially expressed genes related to apomictic and sexual ovule development. The in situ pattern of expression of two selected sequences showed that the differential bands were in reality not exclusively expressed in one stage and one type of reproductive development. Yet, one of the sequences (4-29), similar to a membrane protein, had a pattern of expression that differs in ovules of sexual and apomictic plants and during the stages of ovule development.

    An in situ pattern of expression of a somatic embryogenesis receptor-like kinase gene isolated from Arabidopsis thaliana (AtSERK1) is presented on the sexual and apomictic plant. This gene was expressed in early stages of somatic and zygotic embryogenesis. It is though to play important function in cells with embryonic capacity. In an apomictic and sexual genotypes of Brachiaria decumbens , distinct pattern of expression of this gene was observed in mature ovules before and after anthesis. The occasional expression of this gene before anthesis in the egg apparatus of the apomict pointed to briefly and transiently expression of this gene, that in contrary might be necessary for longer time in the development of the zygotic embryo.

    Finally, the data found in the sexual and apomictic plant of Brachiaria was compiled to characterise the reproduction processes. The existing theories about the origin of apomixis are summarised and some consideration was made based on the data observed in Brachiaria .

    Gramineae
    Sosef, M.S.M. - \ 1999
    Paris : Association de Botanique Tropicale (Flore de Gabon 5bis) - ISBN 9782856542101 - 78
    poaceae - flora - determinatietabellen - identificatie - taxonomie - gabon - poaceae - flora - keys - identification - taxonomy - gabon
    Evapotranspiration of cut over bog covered by Molinia Caerulea.
    Moors, E.J. ; Stricker, J.N.M. ; Abeele, G. van den - \ 1998
    Wageningen : Wageningen Agricultural University (Rapport / Landbouwuniversiteit Wageningen, Afdeling Waterhuishouding 73) - 70
    transpiratie - evapotranspiratie - grassen - poaceae - plantengemeenschappen - zwampen - wetlands - nederland - overijssel - transpiration - evapotranspiration - grasses - poaceae - plant communities - swamps - wetlands - netherlands - overijssel
    Pennisetum section Brevivalvula in West Africa : morphological and genetic variation in an agamic species complex
    Schmelzer, G.H. - \ 1998
    Agricultural University. Promotor(en): L.J.G. van der Maesen; J.F. Renno. - S.l. : Schmelzer - ISBN 9789054858911 - 152
    grassen - poaceae - pennisetum - rassen (planten) - morfogenese - genetische variatie - variatie - west-afrika - grasses - poaceae - pennisetum - varieties - morphogenesis - genetic variation - variation - west africa

    Section Brevivalvula is one of five sections in the large tropical grass genus Pennisetum . It belongs to the tertiary genepool of P. glaucum (L.) R. Br., pearl millet, and consists of six morphological species: P. atrichum Stapf & Hubb., P. hordeoides (Lam.) Steud., P. pedicellatum Trin., P. polystachion (L.) Schult., P. setosum (Swartz) L. Rich. and P. subangustum (Schum.) Stapf & Hubb. P. setosum and P. atrichum are perennials, the other species are annual.

    Four euploid (2x, 4x, 5x, and 6x with x = 9) chromosome levels are known in the section. Tetraploid cytotypes are dominant in all taxa, except P. setosum , which is predominantly hexaploid. Diploids and pentaploids are rare.

    Some of the polyploid cytotypes of P. pedicellatum , P. hordeoides , and P. polystachion are at least partly facultative apomicts, while diploid P. polystachion and P. subangustum are reproducing sexually.

    A morphological analysis showed that all taxa intergrade with at least one other taxon. P. pedicellatum , with one - or more - pedicelled spikelets in large, fluffy involucres, has differentiated from the group with a single sessile spikelet per involucrum, but intermediate plants with one almost sessile spikelet exist as well. The group with a single sessile spikelet shows a gradient from slender plants with scabrous involucral bristles on narrow inflorescences ( P . hordeoides ), to slender plants with hairy involucral bristles on narrow inflorescences ( P.subangustum ), to large plants with hairy involucral bristles on large inflorescences ( P.polystachion ), to large perennial plants with hairy involucral bristles, on large yellowish inflorescences ( P. setosum ). P. atrichum is grouped near P. hordeoides , because of its scabrous involucral bristles, but it is also perennial and rather large.

    Isozyme electrophoresis of 635 plants resulted in 146 different 5-locus genotypes from combinations of 26 alleles. More than 85% of the samples of different species are connected by patterns of identical genotypes. When the proportions of 20 alleles are compared between species, ploidy levels or geographical areas, significant differences are found everywhere. The results also indicate that the samples share the same gene pool.

    These results indicate that the complex is in an active state of evolution. Speciation occurs at a low rate because of sexuality in the diploids as well as facultative apomixis in part of the polyploids, which cause hybridization events among the taxa, obscuring species boundaries. Speciation can become successful when a morphotype finds a specific niche for itself. This is clearly the case for P. pedicellatum , which is better adapted to drier climats than the other taxa. Because of the hybridizations, a fully unambiguous description of the other species of Pennisetum section Brevivalvula is impossible.

    Resultaten van graszaadteeltproeven, oogst 1995
    Borm, G.E.L. ; Wander, J.G.N. - \ 1997
    Lelystad : Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt - 78
    grassen - poaceae - plantenvermeerdering - zaden - grasses - poaceae - propagation - seeds
    Soil-borne plant pathogens of Ammophila arenaria in coastal foredunes
    Rooij - van der Goes, P.C.E.M. de - \ 1996
    Agricultural University. Promotor(en): L. Brussaard, co-promotor(en): J.W. Woldendorp; W.H. van der Putten. - S.l. : De Rooij-van der Goes - ISBN 9789054854784 - 143
    grassen - poaceae - bodem-plant relaties - nematoda - duingebieden - eolisch zand - ammophila arenaria - natuurgebieden - grasses - poaceae - soil plant relationships - nematoda - duneland - aeolian sands - ammophila arenaria - natural areas

    Ammophila arenaria (Marram grass) is the most dominant sand-fixing plant species in the Dutch coastal foredunes. This species has a natural ability to emerge from being buried and is therefore used to stabilize the coastal foredunes. On seaward slopes where plants are buried regularly with windblown sand, plants retain their vigour, but start to degenerate when sand accumulation diminishes. One of the factors that may cause degeneration at stabilized sites is the infection of roots by nematodes and fungi. Burial by fresh windblown sand may enable the plants to overcome these harmful soil organisms. In the present study, the nature of the soil-borne disease and its relationship with sand deposition is investigated. In a field survey, a wide range of nematodes and fungi were isolated from the root zone of A. arenaria . Subsequent inoculation-experiments showed that adding single fungal species did not reduce the growth of seedlings whereas combining all commonly found fungi together did, thus indicating synergistic effects. Adding 80 times more individuals of the semi- endoparasitic nematode Telotylenchus ventralis than present in natural soil reduced the growth of seedlings to the same extent as in natural soil. Several groups of soil organisms, especially those groups that include plant-parasitic nematodes, have shown to affect the growth of A. arenaria Burial with unsterilized root zone sand was less beneficial for plant growth than burial with sterilized or beach sand. This implies that plants are able to escape infection by soil organisms through upward growth following sand accumulation. Fungi colonized the freshly deposited layer of sand faster than plant-parasitic nematodes. Furthermore, it could be shown that in windblown soil numbers of fungal propagules and nematodes were reduced. Rejuvenation of stands along the accumulating edges of blowouts can, therefore, be explained by the reduced inoculum pressure of plant-pathogenic organisms in the deposited soil. The amount of sand and the time when sand is deposited are important components in the chances of A. arenaria to escape infection by soil organisms.
    Opslag en bewaring van Miscanthus giganteus.
    Kortleve, W.J. ; Huisman, W. - \ 1995
    Landbouwmechanisatie 46 (1995)8. - ISSN 0023-7795 - p. 20 - 21.
    bio-energie - biomassa - hakselen - schoonmaken - energie - indeling - grassen - afpellen - planten - poaceae - wassen (activiteit) - nuttig gebruik - voedergrassen - bioenergy - biomass - chopping - cleaning - energy - grading - grasses - peeling - plants - poaceae - washing - utilization - fodder grasses
    The genus Lolium : taxonomy and genetic resources
    Loos, B.P. - \ 1994
    Agricultural University. Promotor(en): L.J.G. van der Maesen; R.G. van den Berg. - S.l. : Loos - ISBN 9789073771116 - 101
    grassen - poaceae - lolium - genenbanken - genetische bronnen - germplasm - hulpbronnenbehoud - genetische bronnen van plantensoorten - taxonomie - plantkunde - iso-enyzmen - enzymologie - plantenanatomie - plantenmorfologie - grasses - poaceae - lolium - gene banks - genetic resources - germplasm - resource conservation - plant genetic resources - taxonomy - botany - isoenzymes - enzymology - plant anatomy - plant morphology

    Several aspects of variation within the genus Lolium, and more in detail within Lolium perenne (perennial ryegrass) have been highlighted. As the results are extensively discussed in each chapter, the general discussion is focused on two aspects of the research.

    Speciation
    It is clear that the genus Lolium is a very variable genus. The variation within the species reduces the clarity of separation of the species. Stebbins (1956) found the differences between Lolium and Festuca not sufficient to justify two separate genera. He also states that the family of Poaceae is a phylogenetically derived family, and therefore of comparatively recent origin. Differences between species and between genera are still developing. In older families, intermediate forms or species have become extinct, therefore genera and species delimitations are clearer in these families, e.g. the Papaveraceae (Stebbins, 1956). Producing additional information besides morphological data, such as cytogenetic studies and biochemical studies, is of little use for these families as genera and species delimitations are easily made with simple morphological characters. In families of more recent origin, such as the Poaceae, as many characteristics as possible should be used to establish the relationships between the species. In Chapters 2, 3 and 4 several types of characters have been analyzed for the genus Lolium. No phylogenetic analysis was performed with these data, only phenetic analysis due to the nature of the characters used. Results indicate that all species, as mentioned in the general introduction, can be recognized, although species delimitations are not unambiguous. Only for L. persicum and L. temulentum the results indicate that these species could possibly be two varieties of one species. All species show diagnostic characters for one ore more of the different type of characters. Although the overlap of species is often unsatisfactory, joining of species would be even more artificial. As speciation is a continuous process it cannot be predicted at which point in time species are going to be sufficiently delimited.

    Man has had large influence on the speciation within Lolium. This is illustrated by the three weedy species within the genus. L. remotum is known as a weed in flax (Hjelmqvist, 1950), L. temulentum and L. persicum are known as weeds in cereals (e.g. Dore, 1950). All three are mimicry weeds, the morphology of the seeds andlor the habit of the plant is similar to the crop in which it grows. Until a few decades back, these three species had a significant impact as weeds, but due to enhanced seed cleaning techniques the distribution area of these species has largely decreased (Hubbard, 1954).

    Other examples of the influence of man on the genus Lolium, are the species L. perenne and L. multiflorum. Their distribution area has largely increased due to sowing by man. Scholz (1975) stated that man has had an enormous influence on the development of both species. According to Scholz (1975), this influence started no more than a few thousand years back, with the cutting and burning of forest for replacement by grassland for cattle, and the discovery of hay making. This has made it almost impossible to determine in which parts of the world both species are indigenous. Not only the distribution area of both species is influenced by man but also the phenotype. Selection changes the phenotype in favour of character states desired by man, such as increased yield. Tyler (1979) observed that after a period in which the standard of management is relaxed, natural phenotypes reoccur. This is confirmed with the results from Chapter 5: Dutch perennial ryegrass populations, collected after a period of more relaxed management, have a distinct phenotype compared to cultivars. Tyler (1979) also indicated that the differences between wild and cultivated forms are extremely blurred for L. perenne. This statement is confirmed by the results from Chapter 6: for allozymic variation, cultivars show absolutely no reduction in variation compared to natural populations. Ellenberg (1963) calls the type of plant as L. perenne semi-domesticated, as the crop is not harvested each year but only kept at an acceptable production level using reseeding. During each phase of their lifecycle, populations are exposed to selection forces. Leading to the situation that in grasslands cultivars are often mixed with plants that have been exposed to enviromnental selection for a number of years. This makes the distinction between natural and cultivated grassland extremely vague.

    Chapter 5 illustrates, as management is the factor that optimizes the amount of genetic variation found within a location, the enormous influence man has had and still has on the amount of variation in phenotypes of L. perenne. Reduction of the influence of man would probably lead to the existence few differing perennial ryegrass phenotypes, and could in some areas even mean extinction of perennial ryegrass. In the Netherlands, foreland and salt marshes are the only original habitats for grassland (Bink et al., 1984). Although L. perenne is a species with much competitive ability, it would suffer from a large reduction of distribution area in case management of grasslands was totally abandoned. Because mainly under man-made conditions, e.g. fertilizing, treading, intensive grazing, drainage, L. perenne expresses this competitive nature.

    For L. rigidum the influence of man is less strong. L. rigidum is used in some parts of the world (e.g. Australia) as a cultivated fodder crop, but in Europe this is not current. In Europe the fate of L. rigidum depends on the perspectives of L. rigidum as a fodder crop in dry areas or as a crossing parent in breeding programmes. Next to its presence in cultivation L. rigidum is well capable to maintain itself under less cultivated circumstances, this in contrast to, especially, L. perenne. Hartley (1956) states that L. rigidum originates from the Mediterranean region and that L. perenne and L. multiflorum originate from the Eurasian region. The ancestral species of the genus Lolium is supposed to have originated in the Mediterranean region (Malik, 1967). This would indicate that L. rigidum could be the wild form for both cultivated species. The relation between wild and cultivated is often confirmed by the reduction of genetic variation within the cultivated forms. Brown (1978) mentions two examples, based on allozyme variation, for which this assumption is valid. Lycopersicon pimpinellifolium has 61 % unique allelic forms compared to those in L. esculentum. Both species share 37% of the allelic variants and 2% is unique for L. esculentum. Oryza perennis has 47% unique peroxidase alleles, and 22% unique esterase alleles, compared to 0. sativa. Both species share 53 % and 78 % of the alleles respectively. The results from Chapter 3 do not indicate a reduction in allelic variation within L. perenne and L. multiflorum, compared to L. rigidum. This indicates that, if L. perenne and L. multiflorum indeed did arise from L. rigidum, this speciation is of recent origin. Phylogenetic relations between species cannot be determined on basis of these data.

    L. loliaceum is not known as a weed nor as a crop plant, it mainly grows under poor and maritime conditions. The influence of man on populations of this species is not large, therefore it is not likely that this species becomes extinct nor that its distribution area will suddenly increase. Phenotypic developments are expected to be gradual and slow.
    For L. canariense the same holds true as for L. loliaceum, it is not a crop nor a weed and grows under poor conditions, making it a stable and localized species.

    The screening of the Lolium species for allozymic variation, added little to the species determination within the genus Lolium. The pattern of allozyme diversity could hardly be linked with taxonomic classification (Chapter 3); mainly because all allelic variants were common in each population screened. As pointed out in the discussion of Chapter 3, this maybe caused by the small number of enzyme systems screened. A question that can be asked is whether increase of the number of allozymes could lead to better results for genotypic screening. In Chapters 3 and 6 the calculated diversity statistics for the cross-breeding Lolium species were above the average for other wind- pollinated cross-breeding species (Hamrick & Godt, 1990). These statistics indicated that a larger proportion than average of the loci screened were polymorphic, and also that the average heterozygosity of the loci was far above the mean. Extension of the number of loci screened would therefore most likely result in finding monomorphic loci or less variable polymorphic loci and would not enhance the results. In literature, analyses of L. perenne populations for several other allozymes are reported. These allozymes are Glutamate- oxaloacetate-transaminase (GOT, Hayward & McAdam, 1977; Arcioni et al., 1988; Charmet et al., 1993), Isocitrate dehydrogenase (IDH: Lallemand et al., 1991; Charmet et al., 1993), Peroxidase (PRX: Charmet et al., 1993) and Superoxide dismutase (SOD: Charmet et al., 1993). All authors report results that confirm the expectation that higher number of allozymes screened do not improve the elucidation of speciation. Again, the within- population variation is too large compared to the betweenpopulation variation.

    Another option would be to make use of molecular markers, e.g. restriction fragment length polymorphism (RFLP). Few reports are known for Lolium species, using these techniques. Darbyshire & Warwick (1992) report on the results for one L. perenne population, which was compared with several other grass populations classified in 26 Festuca species and the genera Vulpia, Poa and Puccinella. Eleven restriction endonucleases and twelve restriction fragments from chloroplast DNA of Petunia hybrida Vilm. were used in this analysis. In total 341 bands were observed of which 108 (31.7%) were polymorphic. Of these 108 bands, 34 were detected in the L. perenne population. Only one plant was analyzed from each population. Chloroplast DNA variation in other Lolium species (Lehväslaiho et al., 1987 ; Soreng et al., 1990) is only reported for one L. multiflorum population, using five restrictionenzymes and direct end labelling. Again only one plant has been analyzed and compared with a large set of populations and genera mainly from the family Poaceae. L. multiflorum differs in 11 bands on a total of 144 shared bands with Festuca pratensis. Only one report is known (Wu et al., 1992) on the between-population variation within L. perenne for RFLP's. Five cultivars of perennial ryegrass were screened, using 2 restriction enzymes and 37 probes from Festuca pratensis. Twenty-four (65 %) of these probes hybridized, resulting in on average 69% polymorphism between the five cultivars . On average 3.2 different banding patterns were observed for each restriction enzyme-probe combination. Again only one plant was analyzed for each population.

    No reports on the between-species and the within-population variation are known for any of the Lolium species.

    The results from Chapter 3 and Chapter 6 indicate that substantial variation is found within populations of the cross-breeding Lolium species, which makes results based on only one plant per population unreliable (Wu et al, 1992). It remains necessary to analyse a minimum number of plants for the crossbreeding Lolium species, unless an acceptable bulk sample can be taken. This would be desirable as otherwise the cost and time needed to analyse a population using molecular markers could be limiting. The danger of using a bulk sample would be that no differences between populations and even between species can be observed (as would be the case for a bulk sample when screening for allozyme variation). Screening of five enzyme systems resulted in a maximum of 10 bands observed ( 13 , if the heterozygous bands were also counted), in case a plant was heterozygous (maximum variation) for each enzyme. This is a much better result as reported by Darbyshire & Warwick (1992), 34 bands out of 132 restriction enzyme-probe combinations. It is equal to the theoretical maximum number of bands reported by Wu et al. (1992), 96 bands in case of heterozygosity at all 48 restriction enzyme-probe combinations. The preliminary conclusion would therefore be that RFLP analysis will not greatly enhance the distinction of crossbreeding Lolium species and populations.

    For the inbreeding Lolium species the analysis of few plants is sufficient. The observed variation would probably increase compared to the observed allozyme diversity (Chapter 3: fixation for four of the five enzymes), as the number of possible markers would greatly increase using RFLP's. The use of molecular markers for the screening of inbreeding Lolium populations would therefore be a valuable extension of the knowledge on these species.

    Genetic resources: in situ conservation
    In the general introduction three research questions were mentioned, concerning the genetic resources of L. perenne. What are the answers to these questions after analyzing the results from four years of research? Firstly, the Dutch populations do form, morphologically, a distinguishable group of forms within the genetic variation for perennial ryegrass. This conclusion is based on the observation of morphological characters only, as the heritability of these characters is better determined than for agronomically important traits as winter hardiness, spring growth etc. The date of ear emergence is one of the most important characters, both agronomically and for the recognition of breeders rights. Results indicate that genetic variation for this character is substantial in the Netherlands: in natural surroundings, populations varying from very early till very late heading could be collected. It is expected that if the Dutch populations show this amount of genetic variation for morphological characters, results can be analogous for agronomical characters. The morphological variation found within the Dutch populations is not comparable with the variation found in the cultivars used in these trials. Although date of ear emergence indicates that some Dutch populations are heading as late as the cultivars, morphologically they are distinct. The Dutch populations are a.o. more prostrate growing and shorter at ear emergence, this could indicate that this phenotype is natural for L. perenne in the Netherlands. The fact that Dutch populations are morphologically clearly distinct from the cultivars and that there was also substantial variation observed between Dutch populations, indicates that in situ conservation is a realistic option for L. perenne. Weibull (1989) gives several advantages and disadvantages for the in situ conservation of forages. The advantages are: continued co-evolution of populations and the possibility to study the ecology of the species. It is also possible to make successive collections, and it avoids space and time consuming activities for storage en regeneration for genebanks. A combination of the genetic resources conservation objective with other objectives like nature conservation could be an option. This possibility is clearly illustrated with the present results, as all Dutch populations were collected in areas managed by nature conservation organisations.

    Disadvantages are that it is difficult to determine how many sites, and which sites should be preserved to optimize genetic variation. Natural populations are vulnerable to external factors, such as human influences and extreme weather conditions. Also the costs of the maintenance of conservation sites maybe high, and access of breeders can be a problem in case of a combination with nature conservation objectives.

    For the allozyme variation no differences between the Dutch populations and the cultivars were found. Allelic variants were very common in all populations, the cultivars showed much larger differences in allelic frequencies than the Dutch populations. In situ conservation would be very successful in retaining genetic diversity at the allozyme level. The data were not useful for selection of accessions for genebanks. Phillips et al. (1993) reported for Avena sterilis L. (inbreeder), the wild progenitor of A. sativa L., the possibility to separate populations in six different groups based on 23 loci. Selection of genebank accessions can be facilitated using these six groups, combined with morphological data.

    Francisco-Ortega et al. (1992) observed for Chamaecytisus proliferus (L. fil.) Link a totally different pattern. Morphologically this species can be separated into seven subspecies, which are morphologically distinct and ecologically each occupy a distinct niche. Allozyme diversity shows no differentiation between these seven subspecies.

    Just like in the genus Lolium, almost all allelic variants are common and widespread, and the within-population variation is very large. Also in this case allozyme data were considered of no use for the selection of genebank accessions.

    Generally, the usefulness of screening for allozyme variation varies substantially. Compatibility behaviour and age of the genus/species are the major factors, explaining the value of this kind of data.

    Graminees du Cameroun
    Zon, A.P.M. van der - \ 1992
    Agricultural University. Promotor(en): L.J.G. van der Maesen; J.F. Veldkamp. - S.l. : Van der Zon
    grassen - poaceae - planten - identificatie - flora - kameroen - voedergrassen - grasses - poaceae - plants - identification - flora - cameroon - fodder grasses

    The grasses are one of the most important plant families of Cameroon. The dry savanas of the North and the mountainous areas of central and western Cameroon are extensive grass areas which are of utmost importance for cattle and fauna in general.

    Several of the importantant traditional agricultural crops such as sorghum, maize and rice are members of the grass family.

    For botanical education and research of plant communities and grasslands the knowledge of grasses is of great importance. At the Cameroonian universities and the Garoua wildlife school there was a great need of a practical grass flora of Cameroon in the french language.

    The first part of the grasses of Cameroon deals with the geology, topography, soils and climate. Next is a discussion of the phytogeography of the grasses and thereafter an overview is given of the prairies and their use by cattle and wildlife.

    Three more or less clear defined plant geographical vegetation zones are distinguished, each of them can be further subdivided: the Soudanian zone (North, and the lower part of the uplands), the Afro-Montaneous zone (the mountains above 2000 m) and the Congo-Guinean zone (forest zone), each with its typical species and genera. The northern slope of the Adamaoua plateau is a clear boundary within the Soudanian zone. The uplands are the richest in species diversity of grasses.

    The open vegetations of Cameroun are often dominated by the grasses, and specimens of these areas are well represented in plant collections. The presence of the Garoua wildlife school has stimulated the knowledge of the vegetation of northern Cameroon. Also around Bamenda (research station Bambui) and on Mt Cameroon many grasses have been collected.

    In the rain forest area of Cameroon the grasses are poorly represented in the collections because of the little importance forest botanists attach to grasses. They generally look upwards instead of downwards and think of grasses as secondary species. However, next to the typical shade-species there are quite a few species typical for the open patches in the forest, in particular along the streams and rivers.

    Of the flora the Andropogoneae are the most striking savana-group and often very dominating. More to the North the Eragrostideae and Aristideae become more important. The Paniceae occur everywhere but are less dominating. A number of smaller bamboo-like groups are shade-tolerant and occur in the rain forest.

    The bend to the south of the vegetation zones as is so obvious in the western Sahel, hardly find expression in Cameroon. Andropogon gayanus is a very clear indicator species in this respect. Although the extreme north of Cameroon has suffered seriously from the drought and the vegetation is very degradated, compared with a few decennia ago no obvious modification of the location of the vegetation zones is visible.

    Grasses are well adapted to fire. Frequent burning causes grasses to dominate. This annual burning is of importance for the cattle as fresh grass becomes available each year. When fires are prevented, the vegetation gets more and more dominated by woody species.

    The wildlife has a more mixed and broader utilisation of the vegetation. More emphasis should be given to a better and sustainable exploitation of this wildlife.

    In the appendix a fist of species is given with notes on the distribution in Cameroon, in Africa and worldwide, and of the most important vegetation types they occur in.

    The second volume of the flore (the Flora) treats the 19 tribes of the grasses, occurring in Cameroon. The lay-out follows the model of the Flore du Cameroun.

    The grass flora of Cameroon is very rich. There are 433 species of grasses, in 125 genera and 19 tribes. Two species new to science are described in the appendix and two new combinations are given.

    Two identification keys are presented, one leading to the tribes and the other to the genera. For each of the tribes and genera keys are provided, leading to the species. For each species there is a description of the general habit, with leaf shape, details on the inflorescences and the spikelets. After the type-indication particulars are given about the habitat, the vernacular names and the uses. There are 120 plates with drawings of 244 species. The microfiches in the back present the herbarium specimens examined. Details include geographic locality and indication where the specimens are lodged with the usual herbarium acronyms (K, L, P, WAG, etc.).

    Influence of Azospirillum spp. on the nitrogen supply of a gramineous host
    Christiansen - Weniger, C. - \ 1991
    Agricultural University. Promotor(en): A.J.B. Zehnder, co-promotor(en): J.A. van Veen. - Arnhem : Christiansen-Weniger - 101
    spirillaceae - spirillum - azospirillum - rizosfeer - grassen - poaceae - assimilatie - stikstof - spirillaceae - spirillum - azospirillum - rhizosphere - grasses - poaceae - assimilation - nitrogen

    The main objectives of this study were to identify factors that control the behaviour of Azospirillum in the rhizosphere of a gramineous plant in order to be able to optimize the association between the bacteria and the host plants in terms of nitrogen supply to the host.

    Plant produced growth substances such as the auxines indole-acetic-acid (IAA) and 2,4-dichlorphenoxy-acetic-acid (2,4 D) or gibberilic acid enhance the acetylene reduction activity of a pure A.brasilense culture. IAA and the cytocinine 6-benzyl-aminopurine also stimulated bacterial growth. It should be pointed out, that Azospirillum also produces IAA itself, which is often mentioned to be the reason of its plant-growth stimulating activity.

    When associated with living roots, the nitrogen fixation (acetylene reduction) activity of Azospirillum brasilense is much less sensitive to the repressive influence of free oxygen and mineral nitrogen, i.e. NO3-and NH4+, than in the absence of an active growing root. Potential acetylene reduction rates varied from 10 to 550 nmol C 2 H 4 h -1plant -1depending on environmental conditions.

    In order to be able to determine the fate of introduced Azospirillum in a soil and in the root environment A.brasilense strains were marked by a transposon (Tn5) insertion into its genome so that reisolation upon double resistance against kanamycin and rifampicin was possible. A.brasilense ::Tn5 established in the rhizosphere of an axenically grown spring wheat to cell numbers as high as 10 6cells per gram dry rhizosphere soil and 10 5cells per gram dry root, respectively. In the rhizosphere of a non-sterile grown plant the number of A.brasilense ::Tn5 was much lower, i.e. approximately 10 4cells per gram dry rhizosphere soil and 10 3cells per gram dry root. The number of A.brasilense ::Tn5 cells was 10 to 100 times higher in the soils closely attached to the roots than in root-free soils. A.brasilense could not be reisolated from inner root-tissue after a root- surface sterilization with 1% chloramine T. When introduced to plants in an early stage of plant growth either by seedling inoculation or by a seed-coating, A.brasilense was able to develop with the growing root and to establish a strong population all over the root.

    Most intensive root colonization of introduced A.brasilense and highest acetylene reduction rates were observed when plants were treated with Azospirillum cells immediately after seedling emergence as compared to the colonization of roots after inoculation at a later stage of growth. Subsequent inoculations during plant development after an initial addition did neither stimulate root colonization nor acetylene reduction activity.

    When comparing wheat and sorghum cultivars with different levels of aluminium tolerance a larger rhizosphere acetylene reduction activity was observed when Azospirillum was introduced to roots of aluminium-tolerant cultivars than to roots of Al- sensitive cultivars. The amount of fixed nitrogen, transferred from Azospirillum to the host as calculated by the 15N dilution technique was also significantly higher in case of Al-tolerant cultivars. Aluminium-tolerant plants appeared to exudate significantly larger amounts of total organic carbon than Al-sensitive plants. Not only the quantity but also the quality of the exudates differed in the sense, that higher concentrations of low molecular dicarbonic acids such as succinic, malic and oxalic acid were observed at root-exudates of aluminium-tolerant wheat plants. These organic acids are known to be preferable carbon substrates for Azospirillum spp, what might explain the more intensive colonization and higher nitrogen fixation capacity in the rhizosphere of Al-tolerant plants.

    Although Azospirillum develops considerable activities in the rhizosphere of host plants the transfer of fixed nitrogen to the host as determined with the 15N-dilution technique appeared to be rather low. Only approximately 3% of the root nitrogen and approximately 2% of the shoot nitrogen was calculated to be derived from the N 2 -fixation activity of the Azospirillum cells.

    In order to enhance the transfer of nitrogen to the host A.brasilense was selected on ethylenediamine, yielding mutant strains which lack their ammonia transport system across cell membranes and which excrete substantial amounts of NH4+, to the environment. Two of these mutant strains fixed nitrogen in the presence of high concentrations (20 mM) of NH4+. Nitrogenase activity of the NIH4+-excreting mutants was two to three times as high as that of the wild type. The mutant strains colonized the roots of axenically grown wheat to high cell numbers and developed rhizosphere acetylene reduction activities comparable to that of the wild type. Both mutant strains caused a significant increase of dry matter production and of total plant N- accumulation as compared to wild type treated plants or to non-inoculated controls. When exposed to a 15[N] 2 enriched atmosphere the A.brasilense mutant strains transfered higher amounts of 15N to their hosts than the wild type did. 15N- enrichment and nitrogen balance studies both indicated that NH4+-excreting A.brasilense support the nitrogen supply of a wheat host.

    Morphological and physiological studies of prairie grass (Bromus willdenowii Kunth)
    Hume, D.E. - \ 1990
    Agricultural University. Promotor(en): L. 't Mannetje. - S.l. : Hume - 163
    bromus - grassen - poaceae - plantkunde - bromus catharticus - bromus - grasses - poaceae - botany - bromus catharticus

    This thesis reports the results of seven indoor and outdoor studies on the growth of prairie grass( Bromus willdenowiiKunth) . In five studies comparisons were also made with ryegrass( Loliumspp.). Leaf and tiller production were quantified for undisturbed growth and growth under different cutting regimes. Water soluble carbohydrate reserves for regrowth were also determined. Particular attention was given to the effects of reproductive development on partitioning of biomass, tillering, herbage quality and yields. Field studies also investigated the effects of disease, plant populations, tillering, natural reseeding and frequency of defoliation.

    Compared to ryegrass, prairie grass had a high leaf appearance rate but low site filling, which resulted in low tiller numbers. Prairie grass had large tillers with long wide leaves, resulting in high herbage production. Plants were able to tiller profusely in the field to compensate for plant death. High reproductive development occurred in prairie grass which had large effects on yields, herbage quality and tillering. Vegetative and reproductive plants performed best under infrequent defoliation regimes.

    Establishment, growth and degeneration of Ammophila arenaria in coastal sand dunes
    Putten, W.H. van der - \ 1989
    Agricultural University. Promotor(en): L. 't Mannetje; C. van Dijk. - S.l. : Van der Putten - 152
    grassen - poaceae - duinen - duinplanten - vegetatie - plantengemeenschappen - vastleggen van duinen - kusten - bescherming - beschermende structuren - versterking - fixatie - stranden - eolisch zand - groei - plantenontwikkeling - nederland - plantenecologie - grasses - poaceae - dunes - duneland plants - vegetation - plant communities - sand dune stabilization - coasts - protection - protective structures - reinforcement - fixation - beaches - aeolian sands - growth - plant development - netherlands - plant ecology

    Introduction

    This study deals with the establishment, growth, and degeneration of Ammophila arenaria (marram grass), a grass species that dominates the vegetation in coastal foredunes. Following natural establishment from rhizomes on high parts of the beach A.arenaria reduces wind velocity, which results in the accretion of windblown sand and the formation of dunes. A. arenaria grows vigorously in mobile dunes where fresh sand is deposited by wind, but it disappears from the vegetation when these dunes become stabilized.

    Because of its ability to stabilize the sand, A. arenaria is often used in dunes to control erosion. It is planted according to a long practicised manual technique, using culms that are collected from stands at the foredune. When foredunes are reconstructed, however, (e.g. after storms) the establishment of A. arenaria is often unsuccessful, which means that erosion control can become very costly.

    This study was carried out to develop new methods of establishing A. arenaria and to investigate the cause of the replant failures on reconstructed dunes. In addition, experiments were carried out to eludicate the relationship between the colonization of windblown sand and the vigour of A. arenaria .

    Establishment

    Two alternative methods were developed: (1) the sowing of seeds, which is rarely practiced and (2) the disk-harrowing of rhizomes, which has not previously been applied.

    Experiments showed that seeds hardly germinate at constant temperatures. A high rate of germination can be achieved with fluctuating high temperatures, but at low temperatures the seeds required stratification in order to germinate. In the field the seeds germinated well if they had been sown during the winter, which was probably because of natural stratification. Seeds can be sown mechanically while afterwards the sand surface needs to be stabilized. For this purpose straw proved to be more effective for seedbed stabilization than spraid compost.

    Rhizomes (i.e. vertical underground stems) were collected from the foredune by mechanical sieving of the sand. Experiments proved that the disk-harrowing of rhizomes was a useful method of establishing A. arenaria provided that the sand surface was temporarily stabilized with straw or planted bundles of reed (chapter 2).

    Growth

    Field experiments showed that higher sowing rates and higher planting densities of rhizomes resulted in higher numbers of seedlings and primary shoots. However, after one growing season production of biomass and numbers of tillers appeared to be independent of the initial density. Application of slow-release NPK fertilizer (Osmocote, 12 to 14 months active at 21 °C) increased dry matter yield and numbers of tillers (chapter 2).

    In a large-scale field experiment, rhizomes and a combination of planted culms and rhizomes produced more biomass and percentage cover than a sown stand during the first growing season. The lowest dry matter yield and percentage cover were obtained with traditionally planted culms. All plantings had been supplied with the same amount of slow- release NPK fertilizer. In the second year, however, the highest production was recorded for planted culms and for seeds in combination with compost. During these two years less than 5 per cent of the total area had to be replanted. All methods, therefore, were satisfactory in terms of sand stabilization.

    The influence of uncontrolled factors was demonstrated by a 100 per cent higher production from a one-year-old stand in 1986 compared to 1987. The origin of the culms and rhizomes also influenced growth. Culms or rhizomes that had been collected from a stable dune with degenerated A.arenaria produced less dry matter and percentage cover than when the plant material was obtained from a mobile dune which was covered by vigorous plants (chapter 3).

    Degeneration

    Growth of seedlings of A.arenaria was strongly reduced in sand from the root zone of a foredune, when compared to growth in fresh (sea) sand. However, no differences occurred when both sand samples were sterilized prior to planting of the seedlings. In sea sand, growth was equal to that in sterilized sand. It was concluded, therefore, that the rhizosphere of A. arenaria contained harmful soil organisms (chapter 4).

    In order to trace the nature of these organisms, biocides (bactericides, a nematicide, and fungicides) were applied to rhizosphere sand, which was planted with seedlings of A.arenaria. Bacteria were not supposed to be involved in the degeneration of A. arenaria , as bactericides did not affect plant growth. The nematicides effectively eliminated endoparasitic
    nematodes ( Heterodera avenae group, Meloidogyne maritima , and Pratylenchus sp.) and the application led to increased plant growth. Fungicides also enhanced growth, however, they also eliminated the nematodes H. avenae and M. maritima. It was concluded that nematodes were involved in the growth reduction and degeneration of A. arenaria, but the involvement of soil fungi could not be established unequivocally. Results of a preliminary inoculation experiment suggested that a complex of soil fungi and nematodes is responsible for the degeneration of A. arenaria (chapters 5 and 8).

    The harmful soil organisms from a certain location reduced growth of local, as well as of foreign populations of A. arenaria. The growth of Calammophila baltica (purple, or hybrid marram grass, a sterile bastard of A. arenaria x Calamagrostis epigejos ) was also reduced by harmful soil organisms, but less than A. arenaria (chapters 4 and 6).

    In three Dutch coastal dune systems harmful soil organisms were detected in the root zones of stable, as well as of mobile foredunes (degenerating and vigorous A. arenaria , respectively), but not in beach sand. The relation between sand deposition by wind and vigorous growth of A. arenaria was explained by supposing that windblown sand, originating from the beach, enables A. arenaria to escape harmful soil organisms (chapter 6). However, within one year after plants had produced new roots in fresh windblown sand, the root system became colonized by harmful soil organisms (chapter 7).

    If harmful organisms were present in the sand prior to root growth, root hair formation was reduced severely and the branching of the roots was stimulated (chapter 7). This deformation of the root system by harmful soil organisms is assumed to be related to the degeneration of A. arenaria. A reduced uptake function and a shallow placement of the root system due to attack by harmful soil organisms in stable dunes increases the susceptibility of the plants to stress of drought, high soil temperatures, and shortage of nutrients. It is concluded that the degeneration of A. arenaria in stable dunes is caused by a combination of harmful biotic factors and abiotic stress.

    Siergrassen (Gramineae, Cyperaceae en Juncaceae).
    Hensen, K.J.W. ; Groendijk-Wilders, N. - \ 1986
    Dendroflora (1986). - ISSN 0374-7247
    crops - cyperaceae - grasses - identification - netherlands - ornamental herbaceous plants - plants - poaceae - taxonomy - varieties
    Competition between a maize crop and a natural population of Echinochloa crus-galli (L.) P.B.
    Kropff, M.J. ; Vossen, F.J.H. ; Spitters, C.J.T. ; Groot, W. de - \ 1984
    Netherlands Journal of Agricultural Science 32 (1984). - ISSN 0028-2928 - p. 324 - 327.
    biologische mededinging - grassen - maïs - parasitaire planten - concurrentie tussen planten - plantenecologie - poaceae - onkruiden - zea mays - biological competition - grasses - maize - parasitic plants - plant competition - plant ecology - poaceae - weeds - zea mays
    In een veldexperiment werd de groeireductie op mais tengevolge van de competitie door een hanepootpopulatie onderzocht. Bij een dichtheid van 100 planten per m2 werd de opbrengst van mais teruggebracht tot 18%. Deze reductie verschilde aanmerkelijk tussen de jaren als gevolg van het grote verschil in opkomst van zowel hanepoot als mais. Een simulatiestudie voor de competitie van licht en water bevestigde deze aanname
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