Specificity, pathogenicity and population dynamics of the endoparasitic nematode Heterodera arenaria in coastal foredunes Promotoren Prof. Dr. L. Brussaard Hoogleraar Bodembiologie en biologische bodemkwaliteit Prof. Dr. Ir.J.W . Woldendorp Hoogleraar Biologie van de rhizosfeer Co-promotor Dr. Ir. W.H. vande r Putten Werkgroepleider Multitrofe Interacties Nederlands Instituut voor Oecologisch Onderzoek Samenstelling promotiecommissie Prof. Dr. Ir.J . Bakker (Wageningen Universiteit) Dr. R. Cook (Institute of Grassland and Environmental Research, Wales,UK ) Prof. Dr. E. van der Meijden (Rijksuniversiteit Leiden) Prof. Dr.J.A . vanVee n (Rijksuniversiteit Leiden) Christine Dieuwke van der Stoel Specificity, pathogenicity and population dynamics of the endoparasitic nematode Heterodera arenaria in coastal foredunes Proefschrift ter verkrijging van de graad van doctor op gezag van de rector magnificus van Wageningen Universiteit, prof. dr. ir. L. Speelman, in het openbaar te verdedigen op dinsdag 25 September 2001 des namiddags te vier uur in de Aula. \o Z^ ^ Van der Stoel, CD. Specificity, pathogenicity and population dynamics of the endoparasitic nematode Heterodera arenariai n coastal foredunes. PhD Thesis Wageningen University - with references - with summary in Dutch. ISBN 90-5808-436-1 STELLINGEN 1. Dynamiek in debuitenduinen , vooral door zandoverstuiving, bevordert de instandhoudingva npopulatie sva nd ecystennematod eHeterodera arenaria (dit proefschrift). 2. De populatiegrootte van Heterodera arenaria wordt in belangrijke mate gereguleerd door dehoeveelhei d helmwortels (dit proefschrift). 3. Voor het begrijpen van de rol van nematoden in successie in de vegetatie van de buitenduinen dienen meer soorten, evenals hun samenhang met anderebodemorganismen , bestudeerd teworde n danzij n onderzochti nhe t onderzoek beschreven in dit proefschrift. 4. Deseizoensmobilitei t vanplantenparasitair e nematoden isi nduine ngrote r dan diei n landbouwgronden. 5. Onderzoek naar interacties tussen planten, bodempathogenen en hun antagonisten in natuurlijke ecosystemen kan bijdragen aan het vaststellen van de mogelijkheden en beperkingen van biologische bestrijding in landbouwsystemen. 6. De doorvoering van een andere puntentelling in sporten zoalsvolleyba le n badminton methe t doeld espor t aantrekkelijker temaken ,maak the tallee n aantrekkelijker voord ezappend esportkijke r diegee nverstan d heeft vand e betreffende sport. 7. Onnodig links blijven rijden op de snelweg tijdens spitsuren is een belangrijke veroorzaker van files. 8. De bestrijding van bacterien en ongedierte in en om het huis neemt ongezonde vormenaan . Stellingen behorende bij het proefschrift 'Specificity, pathogenicity and population dynamics of the endoparasitic nematode Heterodera arenaria in coastal foredunes' Inekeva n der Stoel Wageningen, 25Septembe r 2001 ABSTRACT Van der Stoel, CD., 2001. Specificity, pathogenicity and population dynamics of the endoparasitic nematode Heterodera arenaria in coastal foredunes. PhD thesis, Wageningen University and Research-centre, Wageningen, The Netherlands, 135pp. In natural ecosystems hardly any attention has been given to the population dynamics of plant-parasitic nematodes. In coastal foredunes, plant-parasitic nematodes are supposed to be involved in the degeneration and succession of the dominant sand-fixing grass Ammophila arenaria(Marra m grass). The specificity, pathogenicity and population dynamics of the sedentary endoparasitic nematode Heterodera arenaria have been studied to determine if this species might be a key component of the soil pathogen complex of ^4. arenaria. H. arenaria was found to be specific to Elymusfarctus and A. arenaria in the mobile area of the coastal foredunes. Colonisation of the newly deposited sand layer by H. arenaria corresponded well with the development of pathogenicity in a series of bioassays. However, direct addition of the nematode to A. arenaria did not result in growth reduction of the plant. So, H. arenaria behaves like a biotrophic parasite, which has a high specificity but is not aggressive. Therefore, H. arenaria did not seem to be direcdy involved in the degeneration of A. arenaria. Each year, the majority of the population of new H. arenaria cysts develops in the newly deposited sand layers. These layers are colonised by A. arenaria roots throughout the growing season. Migration to the new root layer may offer an individual nematode the benefit of early development and a larger potential offspring. The continuous release of juveniles in the field and their development in experiments indicate that release of juveniles from cysts is an ultimately determined process. Juveniles were found to emerge in November and many eggs or juveniles did not survive the winter period. The strategy of release, however, seems effective; the distance of migration could be too large to detect specific cues from the plant and the start of root formation in the field is highly variable. The emergence of juveniles late in the growing season could result in a second generation within the same year. The constant number of cysts per gram of roots suggests that the population density of H. arenaria is most likely a bottom-up directed process. Keywords: Heterodera, plant-parasitic nematodes, soil pathogens, Ammophilaarenaria, occurrence, abundance, specificity, population dynamics, life history, pathogenicity, PCR-SSCP, molecular method, escape, sand burial, dispersal, migration, fitness, development time, survival, reproductive success, bottom-up, top-down. CONTENTS Chapter 1 General introduction Chapter 2 Colonisation of the root zone of the clonal grass Ammophila arenariab y nematodes and the development of pathogenicity Chapter 3 Rapid identification of cyst (Heterodera spp., Globodera spp.) and root-knot (Meloidogyne spp.) nematodes on the basis of ITS2 sequence variation detected by PCR-SSCP (PCR-Single-Strand- Conformational Polymorphism) in cultures and field samples 29 Chapter 4 Host status of successional coastal foredune plant species and pathogenicity of the endoparasitic nematode Heterodera arenaria 45 Chapter 5 What controls the population dynamics of plant-parasitic nematodes in natural ecosystems? The cyst nematode Heterodera arenaria and the clonal grass Ammophila arenariai n outer coastal dunes as a model 63 Chapter 6 Dispersal-related performance of the cyst nematode Heterodera arenaria after sand deposition in outer coastal foredunes 83 Chapter 7 General discussion 103 References 111 Summary 125 Samenvatting 129 Nawoord 133 Curriculum vitae 135 CHAPTER 1 GENERAL INTRODUCTION Soilpathogens in naturalecosystems Soil-borne pathogens in natural vegetation have already briefly been mentioned in a book by Clements (1928), but one of the first reports presenting experimental evidence on the role of soil pathogens in natural vegetation originates from Oremus and Otten (1981). They suggested that plant-parasitic nematodes are involved in the natural decline of the dune shrub Hippophae rhamnoides (Sea Buckthorn). Since then this topic is getting more and more attention, although the actual mechanisms are still poorly understood, and there is uncertainty about the actual species involved (Troelstra eta/., 2001). Most studies in recent years have focused on the influence of pathogenic soil fungi on plant communities. Pythium spp. and Phytophthoraspp . are fungal species known to negatively affect plant growth. In temperate and tropical trees and also in annual plants soil-borne fungi cause seedling mortality, which affects the spatial and temporal distribution of plant species in the vegetation (Augspurger, 1983, 1990; Mihail eta/., 1998; Packer and Clay, 2000; Alexander and Mihail, 2000). In later stages of plant growth examples are known from the whole range of vegetation types from grasslands up to forests in which the soil community may negatively affect the growth of specific plant individuals or species, thereby contributing to the spatio-temporal processes in natural vegetation (Bever, 1994; Bever etal, 1997; Holah etal, 1997;Mill s and Bever, 1998). As regards plant-parasitic nematodes in natural vegetation, most is known from grasslands. The role of nematodes in spatio-temporal processes has been studied in coastal dune grasses, meadows, and prairie grasses (Stanton, 1988; Van der Putten et a/., 1990; De Rooij-Van der Goes, 1995; Van der Veen, 2000; Blomqvist et a/., 2000; Olff et a/., 2000; Verschoor, thesis in prep.). For the rest, studies on nematodes in natural vegetation mainly concentrate on two aspects. Some studies examine the taxonomy of species and focus on the morphological description of plant-parasitic nematodes {e.g. Sturhan, 1996; Robinson eta/., 1996; Karssen eta/., 1998a,b, 2000). Others investigate the species composition of whole nematode assemblages and their distribution in space or time, mostly dividing the nematodes in different feeding groups, such as fungal feeders, bacterial feeders or CHAPTER 1 plant feeders (Wasilewska, 1970, 1971; Magnusson, 1983; Freckman and Virginia, 1989; Bussau, 1991; De Goede */ al, 1993; Hodda and Wanless, 1994; Yeates, 1996; De Goede and Bongers, 1998). To our knowledge very little is known of the population dynamics of plant- parasitic nematodes in natural vegetation, which is the subject of the present thesis. Plant-parasitic nematodes Organisms that belong to the phylum of the Nematoda are in general transparent worm-shape invertebrates. Within the Nematoda, the ubiquitous plant- parasitic nematodes are generally too small