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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Screening opslagbestrijding raaigrassen in rietzwenkgras
    Zeeland, M.G. van; Hoek, H. - \ 2009
    Kennisakker.nl 1009 (2009)22 juli.
    gewasbescherming - onkruidbestrijding - grassen - lolium - festuca arundinacea - herbiciden - zaden - opslag (planten) - graszaden - zaadproductie - akkerbouw - plant protection - weed control - grasses - lolium - festuca arundinacea - herbicides - seeds - volunteer plants - grass seeds - seed production - arable farming
    Opslagbestrijding van raaigrassen in rietzwenkgras is zowel in eerste- als tweedejaars rietzwenkgras een probleem. In 2003 gaf de graszaadsector aan behoefte te hebben aan geschikte herbiciden om deze opslag te bestrijden. Daarom werd in 2004 een screeningsproef in Biervliet aangelegd. Chloor-IPC (toegelaten in rietzwenkgras) en één experimenteel middel kwamen als meest perspectiefvolle middelen uit deze proef. In 2005 werd vervolgens een deugdelijkheidsproef in Axel aangelegd, waarbij ook andere mogelijke geschikte middelen werden getoetst. Het experimentele middel, dat in 2004 in de screeningsproef was beproefd, bleek in 2005 wederom voldoende effectief en redelijk selectief.
    Teelthandleiding graszaad - schimmelziekten
    Borm, G.E.L. - \ 2005
    Kennisakker.nl 2005 (2005)15 juni.
    grassen - gewasbescherming - lolium - blumeria graminis - meeldauw - roestziekten - puccinia - puccinia coronata - monographella nivalis - sneeuwschimmel - oculimacula yallundae - bladvlekkenziekte - drechslera - ascochyta - puccinia poarum - moederkoren - claviceps purpurea - zaden - akkerbouw - schimmelziekten - fungiciden - plantenziekteverwekkende schimmels - graszaden - zaadproductie - teelthandleidingen - grasses - plant protection - lolium - blumeria graminis - mildews - rust diseases - puccinia - puccinia coronata - monographella nivalis - snow moulds - oculimacula yallundae - leaf spotting - drechslera - ascochyta - puccinia poarum - ergot - claviceps purpurea - seeds - arable farming - fungal diseases - fungicides - plant pathogenic fungi - grass seeds - seed production - cultivation manuals
    In de graszaadteelt kan een aantal specifieke schimmels van betekenis zijn. In hoeverre ze van invloed zijn voor de zaadproductie, is slechts van een enkele aantasting bekend. In dit hoofdstuk wordt allereerst een korte beschrijving gegeven van de belangrijkste ziekten. Vervolgens wordt ingegaan op de effecten van de toepassing van fungiciden.
    Interacties tussen lijnen van groenbemesters en isolaten van Meloidogyne chitwoodi en M.fallax
    Zoon, F.C. ; Poleij, L.M. ; Kruijssen, L. van; Schlathoelter, M. - \ 2005
    groenbemesters - meloidogyne - raphanus sativus - lolium - interacties - green manures - meloidogyne - raphanus sativus - lolium - interactions
    Poster met onderzoeksresultaten. Interacties tussen lijnen van Bladrammenas (BR) en Italiaans Raaigras (IR) en isolaten van wortelknobbelaaltjes (Meloidogyne chitwoodi en M.fallax) werden onderzocht om de aggressiviteit (virulentie) van isolaten vast te stellen en de genetische achtergrond van deze relaties te verkennen
    Literatuurstudie van landbouwkundige aspecten van herinzaai van grasland
    Boer, H.C. de; Hoving, I.E. - \ 2005
    Lelystad : Animal Sciences Group (Praktijkrapport / Animal Sciences Group, Praktijkonderzoek : Rundvee ) - 27
    graslanden - rundveeteelt - zaaien - lolium - opbrengsten - voedingswaarde - voeropname - mestresultaten - literatuuroverzichten - nederland - grasslands - cattle farming - sowing - lolium - yields - nutritive value - feed intake - fattening performance - literature reviews - netherlands
    This survey discusses the effect of reseeding botanically deteriorated grassland on several aspects of grassland use, including dry matter yield, intake of grass during grazing, nutritive value, ensilability, conservation losses, intake of silage and utilisation in the animal. From the survey it appears that a number of relatively small differences on several aspects can result in a 24-30 % higher productivity (beef production) of reseeded grassland compared with botanically deteriorated grassland.
    Durable resistance against Meloidogyne spp. possible for italian ryegrass?
    Kruijssen, L. van; Nes, M. van; Loeffen, E. ; Jager, J. ; Zoon, F.C. ; Poleij, L.M. - \ 2003
    lolium - graslandbeheer - gewasbescherming - genetische gewasbescherming - meloidogyne - resistentie van variëteiten - resistentieveredeling - lolium - grassland management - plant protection - genetic control - meloidogyne - varietal resistance - resistance breeding
    The variation in resistance to Meloidogyne chitwoodi and M. fallax in italian ryegrass has been studied in order to breed more resistant ryegrass varieties.
    A dairy system based on forages and grazing in temperate Mexico
    Amendola, R.D. - \ 2002
    Wageningen University. Promotor(en): L. 't Mannetje; E.A. Lantinga. - S.l. : S.n. - ISBN 9789058085870 - 269
    melkveehouderij - ruwvoer (forage) - begrazing - beweidingssystemen - maïskuilvoer - luzerne - grassen - lolium - concentraten - diervoedering - bijvoeding - tropische graslanden - graslandbeheer - stikstof - stikstofmeststoffen - irrigatie - veebezetting - dierlijke productie - rentabiliteit - dairy farming - forage - grazing - grazing systems - maize silage - lucerne - grasses - lolium - concentrates - animal feeding - supplementary feeding - tropical grasslands - grassland management - nitrogen - nitrogen fertilizers - irrigation - stocking rate - animal production - profitability

    Mexican dairy farmers will face in the near future the challenge of increased competition and the strategy to survive this at farm level will have to be based on competitive free trade world prices. This thesis describes the design of a dairy system based on forages and grazing to reduce production costs in temperate Mexico. This dairy system is based on a sequential cropping system of permanent pastures of alfalfa and orchard grass, winter annual pastures of oats and annual ryegrass and silage maize. Between May and October the cows graze on permanent pastures and between November and April they graze both types of pastures. Between October and April the cows also receive supplementary feeding with maize silage. The cows are supplementarily fed with moderate amounts of concentrates during the lactation. The responses of stocking rate and milk production per hectare to increasing levels supplementary feeding with maize silage and concentrates were studied in two experiments. In both experiments a high and uniform pasture utilisation was targeted irrespective of the level of supplementary feeding. Milk production per hectare was more closely affected by changes in stocking rate than by changes in production per cow. Supplementary feeding with maize silage up to 4.8 kg DM of silage cow -1day -1and 4 kg of concentrate cow -1day -1appeared to be economically feasible. The right economic decision could not have been based on the response in milk production per cow to supplementary feeding. The allowance - intake relationship for dairy cows grazing oats and annual ryegrass pastures is reported. The responses of herbage intake and composition of the ingested herbage to different levels of herbage allowance were used to identify the levels of stocking rate and height of residual herbage that maximised production per unit of area. The number of bites taken per unit of area appeared to be an adequate variable to interpret the responses to herbage allowance. The effects of nitrogen fertilisation and irrigation on herbage and nitrogen yield of oats and ryegrass pastures were evaluated in a cutting trial. Nitrogen fertilisation between 50 and 100 kg N ha -1harvest -1increased herbage production, reduced the cost of produced herbage and improved the efficiency of utilisation of irrigation water. Using a high level of irrigation reduced the efficiency of utilisation of irrigation water and the recovery of fertilizer-N. However, increasing the frequency of irrigation increased the efficiency of use of absorbed N. The results of two years of operation (1998 and 1999) of the Farmlet for Dairy Production Under Grazing of Chapingo University are reported. The average stocking rate was 2.6 cows ha -1, the average production per cow was 6200 kg milk per lactation and the average productivity was 16 Mg milk ha -1year -1. Feeding costs in this dairy system were 43% lower than the average feeding costs in prevailing dairy systems. The net revenues (1273 US $ ha -1year -1) indicate that this dairy system is a feasible option. Based on these results, an improved pasture-crop rotation is proposed with a targeted productivity of 29 Mg milk ha -1year -1.

    Modelling interactions in grass-clover mixtures
    Nassiri Mahallati, M. - \ 1998
    Agricultural University. Promotor(en): L. 't Mannetje; A. Elgersma; E.A. Lantinga. - S.l. : Mahallati - ISBN 9789054858201 - 165
    graslanden - lolium - trifolium repens - stikstof - biologische mededinging - concurrentie tussen planten - plantenecologie - licht - fotoperiode - fotoperiodiciteit - schaduw - fotosynthese - computersimulatie - simulatie - simulatiemodellen - lolium perenne - grasslands - lolium - trifolium repens - nitrogen - biological competition - plant competition - plant ecology - light - photoperiod - photoperiodism - shade - photosynthesis - computer simulation - simulation - simulation models - lolium perenne

    The study described in this thesis focuses on a quantitative understanding of the complex interactions in binary mixtures of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) under cutting. The first part of the study describes the dynamics of growth, production and the structural characteristics of contrasting grass and clover cultivars under field conditions. This basic information is used in the second part to quantify light absorption, C0 2 assimilation, radiation use efficiency (RUE) and light competition of the species using a modelling approach.

    Both species showed a seasonal pattern in growth of the dry matter (DM) and leaf area index (LAI) during the season so that the grass-dominated swards during spring shifted to clover dominance in summer. Without N fertilisation (-N), this seasonality was mainly controlled by the weather conditions. However, in fertilised mixtures (+N) grass was the dominant component of the mixture during the whole season and clover growth was always limited by light. The competitive ability and persistence of clover were determined by the structural characteristics of the cultivars. In the -N swards, both large and small-leaved clover cultivars had a higher proportion of their leaf area at the top canopy layers than their companion grass. In the +N mixtures, this was observed only in largeleaved clover, whereas the small-leaved cultivar was strongly overtopped. The difference between cultivars; was mainly due to the pattern of allocation of the DM into the supporting tissues.

    Experimental results showed two sources of vertical heterogeneity within the mixed grass-clover canopies: different patterns of LAI distribution and leaf dispersion. The validity of the canopy light partitioning model was considerably improved by introducing these sources of variation into the model. Using this model the RUE of species was calculated for different regrowth periods. Grass and clover had a different RUE in mixture and monoculture, but overall RUE was higher in grass, particularly in spring. The variation in the DM yield of grass under different treatments was due to changes in RUE and absorbed radiation. However, in clover these differences were mainly due to the amount of absorbed radiation. Quantification of light competition showed that in spring grass was the strongest competitor. In summer, the competitive ability of clover was related to N level and clover cultivar. Without N, both large and small-leaved clover were better competitors than grass. However, in the +N swards only the large-leaved clover had the same competitive ability as its companion grass. In both species a leaf N profile developed during regrowth, parallel to the light profile within the canopy. The effect of the observed compared to a uniform leaf N profile on canopy C02 assimilation of species was low, but it was different between mixtures and monocultures.

    It was concluded that the effect of canopy structure on productivity of species was more important than their assimilatory characteristics. The persistence of white clover under cutting may be improved by choosing cultivars with a higher competitive ability, based on canopy structure.

    Physiological constraints to seed growth in perennial ryegrass (Lolium perenne L.)
    Warringa, J.W. - \ 1997
    Agricultural University. Promotor(en): P.C. Struik; A.J.C. de Visser. - S.l. : Warringa - ISBN 9789054856337 - 139
    lolium - plantenfysiologie - plantenontwikkeling - vruchten - rijp worden - formatie - distributie - voedingsstoffenreserves - lolium - plant physiology - plant development - fruits - ripening - formation - distribution - nutrient reserves

    The yield of a seed crop of perennial ryegrass varies between I and 2 Mg/ha. This variation is caused by variation in the number of seeds that reach an adequate dry weight. On average 70 % of the seeds present before harvest and cleaning are not recovered because of their low weight. This suggests that seed filling and not seed set determines to a large extent seed yield. Factors influencing seed filling were studied on spaced plants in the greenhouse.

    Reducing the light intensity after anthesis from 115 % to 24 % (1.1 MJ/m2) showed that the amount of carbon assimilates in the reproductive tiller was not limiting to seed filling. Seed yield per ear was reduced by only 14 % and average seed dry weight by only 4 %. Although the amount of water-soluble carbohydrates (WSC in the stem + rachis was strongly reduced at 24 % light, it could have supported an extra 37 % of seed yield.

    New vegetative tillers that developed after anthesis did not reduce seed filling and seed yield per ear because of the large amount of WSC reserves in the stem. Regrowth of tillers cut at anthesis strongly reduced WSC stem reserves.

    The large variation of seed dry weight within the ear could for about 60 % be attributed to differences in rate of growth and for about 30 % to differences in duration of growth. The differences in growth rate were determined by the ovule dry weight at anthesis and not by differences in relative growth rate. The availability of assimilates and the accumulation of starch did not differ between seeds within the ear. Differences in the duration of growth were mainly caused by differences in time of anthesis, not ripening. The interaction between seeds in the ear was weak; removal of spikelets or seeds within a spikelet did not strongly affect the remaining seeds. Apparently processes in the seed itself mainly determine seed filling and seed yield of perennial ryegrass. Factors controlling ear development determine the ovule dry weight at anthesis and thus to a large extent the variation in final seed dry weight within the ear.

    Hoogproduktieve rassen van Engels raaigras gunstig voor stikstofbenutting
    Sikkema, K. - \ 1995
    Praktijkonderzoek / Praktijkonderzoek Rundvee, Schapen en Paarden (PR), Waiboerhoeve 8 (1995)6. - ISSN 0921-8874 - p. 28 - 30.
    cultivars - graslanden - lolium - stikstof - stikstofmeststoffen - rassen (taxonomisch) - rassen (planten) - cultivars - grasslands - lolium - nitrogen - nitrogen fertilizers - races - varieties
    Met het oog op vermindering van de N-verliezen is het van belang te weten hoe de stikstofbenutting van de verschillende grasrassen en grassoorten zich onderling verhouden.
    Naweiden met schapen geeft meer Engels raaigras
    Boer, J. de; Sikkema, K. - \ 1995
    Praktijkonderzoek / Praktijkonderzoek Rundvee, Schapen en Paarden (PR), Waiboerhoeve 8 (1995)1. - ISSN 0921-8874 - p. 51 - 53.
    dieren - geiten - graslanden - begrazing - lolium - plantensuccessie - schapen - verstoring - animals - goats - grasslands - grazing - lolium - plant succession - sheep - disturbance
    Bij deze lage veebezetting is geen effect gevonden van schapenbeweiding op de zodedichtheid en draagkracht.
    Chemische bestrijding van ruwbeemdgras in Engels raaigras
    Baltus, P.C.W. ; Weide, R.Y. van der - \ 1994
    In: Jaarboek 1993-1996 : verslagen van afgesloten onderzoeksprojecten op de regionale onderzoekcentra en het PAGV. Akkerbouw Lelystad : Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond [etc.] (Publikatie / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond, Regionale Onderzoekcentra No. 70a-81A) - p. 152 - 156.
    herbiciden - lolium - gewasbescherming - poa - herbicides - lolium - plant protection - poa
    Invloed stro-management na eerste oogst Engels raaigras (Lolium perenne) en herfststikstofbemesting op tweede oogst
    Wander, J.G.N. ; Schouten, E.T.J. - \ 1994
    In: Jaarboek 1993-1996 : verslagen van afgesloten onderzoeksprojecten op de regionale onderzoekcentra en het PAGV. Akkerbouw Lelystad : Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond [etc.] (Publikatie / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond, Regionale Onderzoekcentra No. 70a-81A) - p. 87 - 91.
    herfst - lolium - stikstofmeststoffen - stro - autumn - lolium - nitrogen fertilizers - straw
    De effecten van stro-management (afvoeren, hakselen of verbranden) en van herfststikstofbemesting op de gewasgroei, de zaadopbrengst, het duizendkorrelgewicht en de kiemkracht van Engels raaigras zijn in 6 proeven onderzocht
    Perspectieven grassenveredeling voor bedrijfsinkomen en mineralenoverschotten = Impact of grass breeding on farm income and mineral surplusses
    Vellinga, Th.V. ; Loo, E.N. van - \ 1994
    Lelystad : Proefstation voor de Rundveehouderij, Schapenhouderij enPaardenhouderij (Rapport / Proefstation voor de Rundveehouderij, Schapenhouderij en Paardenhouderij P.R. 151) - 57
    lolium - selectie - selectieresponsen - mineralen - boekhouding - stikstof - melkvee - melkveehouderij - nederland - lolium - selection - selection responses - minerals - accounting - nitrogen - dairy cattle - dairy farming - netherlands
    Towards in vitro fertilization, gametosomatic cybridization and DNA transfer in perennial ryegrass (Lolium perenne L.)
    Maas, H.M. van der - \ 1994
    Agricultural University. Promotor(en): J.L. van Went; F.A. Krens. - S.l. : Van der Maas - ISBN 9789054851981 - 99
    selectie - selectieresponsen - somatische hybridisatie - soortkruising - hybriden - lolium - heritability - genetica - overerving - selection - selection responses - somatic hybridization - interspecific hybridization - hybrids - lolium - heritability - genetics - inheritance

    In this thesis, research towards invitro fertilization, gametosomatic cybridization andDNAtransfer in perennial ryegrass ( Loliumperenne L.), the most important forage grass of North West Europe is described. Techniques for in vitro fertilization and gametosomatic cybridization were aimed at developing a new regeneration technique allowingDNAmodification of perennial ryegrass byDNAtransfer or by transfer of cytoplasmic traits. For this, isolation and storage techniques for sperm cells and egg cells were developed. The isolated sperm cells proved to be haploid and exhibited a moderate cytological variability. They contain only a small number ofDNAcontaining organelles, which renders these cells suitable as nucleus donors in cybridization experiments. The morphology of isolated egg cells was comparable to the morphology of egg cells in situ of other monocotyledons and angiosperms in general. The most likely option to obtain in vitro fertilization and gametosomatic cybridization between, respectively, egg cells and sperm cells and sperm cells and cytoplasts, will be one to one fusion under microfusion conditions. Furthermore, to analyze whether promoters of rice genes are adequate for transgene expression in perennial ryegrass a method for direct gene transfer was developed. Stable transformation was obtained using biolistic bombardment of a non embryogenic cell suspension culture. The constitutive promoter of the rice gene GOS2 proved suitable for expression of a transgene in perennial ryegrass. For production of transgenic plant material in the near future, biolistic bombardment of an embryogenic cell suspension or of other regenerative tissues, will be a more realistic option than via in vitro fertilization as regeneration technique inDNAtransfer experiments. The performed research has created a broad basis for further research aimed at both cybridization, using sperm cells as nucleus donors, and direct gene transfer in perennial ryegrass, as well as at topics such as gamete interaction, zygote formation and early embryogenesis of higher plants at the cellular and molecular level.

    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.

    Zaadvorming bij grassen, in het bijzonder bij Lolium perenne : een literatuuronderzoek
    Warringa, J.W. - \ 1993
    Wageningen : CABO-DLO (Verslag / Dienst Landbouwkundig Onderzoek, Centrum voor Agrobiologisch Onderzoek 183) - 42
    vruchtzetten - vruchtdragend - lolium - overzichten - fruit set - fruiting - lolium - reviews
    Reactie van graszaad op fosfaattoestand en fosfaatbemesting : verslag van veldproeven met veldbeemd-, roodzwenk- en Engels raaigras (1989 - 1991)
    Steenhuizen, J.W. ; Wander, J.G.N. ; Ehlert, P.A.I. - \ 1993
    Haren etc. : IB-DLO [etc.] (Rapport / IB-DLO ) - 65
    lolium - fosfor - fosformeststoffen - bodem - lolium - phosphorus - phosphorus fertilizers - soil
    Herfstbehandeling van Engels raaigras bestemd voor de eerste en tweede zaadoogst en van veldbeemd en roodzwenk bestemd voor de tweede of latere zaadoogst op kleigronden = Autumn treatment of perennial ryegrass intended for the first and second seed - harvest and of smooth - stalked meadowgrass and red fescue intended for the second or later seed-harvest on clay soils
    Borm, G.E.L. - \ 1993
    Lelystad : PAGV (Verslag / Proefstation voor de Akkerbouw en de Groenteteelt in de Vollegrond nr. 162) - 157
    lolium - zaadproductie - zaadbehandeling - lolium - seed production - seed treatment
    Verteerbaarheid bij Engels raaigras : invloed van maaitijdstip en snede op de eigenschappen, die van belang zijn voor de voederwaarde van Engelse raaigrasrassen : rapport van een speciale maaiproef te Dronten in 1990 t/m 1992
    Ebskamp, A.G.M. - \ 1993
    Wageningen : CPRO-DLO - 45
    verteerbaarheid - voer - lolium - digestibility - feeds - lolium
    On the relation between tillering, leaf area dynamics and growth of perennial ryegrass (Lolium perennne L.)
    Loo, E.N. van - \ 1993
    Agricultural University. Promotor(en): L. 't Mannetje; R. Rabbinge. - S.l. : Van Loo - ISBN 9789054851547 - 169
    polariteit - interacties - wortels - scheuten - lolium - ontbladering - polarity - interactions - roots - shoots - lolium - defoliation
    Modern intensively managed grasslands are subject to sward deterioration as a result of urine scorching, treading, winter mortality and late mowing or grazing. The major species in Dutch grasslands is perennial ryegrass. Deterioration consists of a decreasing presence of this species through death of tillers and plant. This gives rise to open swards which are subject to weed invasion and leads to a reduced productivity and nitrogen recovery. The objectives of this study were to increase the understanding of the recovery potential of open perennial ryegrass swards and of the relation between tiller density and herbage accumulation. Tiller production, tiller mortality, leaf area dynamics and growth as affected by cutting treatment, water availability, nitrogen supply and plant density were studied in field, glasshouse and phytotron experiments. The relative tiller appearance rate was studied as the product of leaf appearance rate and site filling. Leaf appearance rate was highly positively correlated with temperature and negatively with cutting height. Cutting frequency had no effect. Leaf appearance rate was reduced by low water potential and low nitrogen supply. Site filling decreased with decreasing nitrogen supply and increasing leaf area index. Just after defoliation, site filling was lower than later after defoliation, because of low substrate availability to developing tiller buds. In studying the effect of low and high nitrogen supply, genetic variation was found in nitrogen use efficiency. Populations with a high nitrogen use efficiency and a high herbage accumulation rate, also had a high leaf weight ratio and high tillering capacity. Models were developed for the simulation of changes in tiller number, leaf area expansion and dry matter accumulation of spaced plants and swards. These models were used for sensitivity analyses of the effect of leaf area expansion rate and leaf weight ratio on regrowth after defoliation and for the analysis of the importance of substrate availability for tillering and regrowth. The field experiments and the sward model showed that even with very low seeding rates, the amount of herbage harvested in the second harvest year is not lower than at very high seeding rates. Therefore, it was concluded that only when a low tiller density coincides with a clumped distribution of tillers and with a high frequency of patches without perennial ryegrass, reseeding of perennial ryegrass swards should be considered.
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