Host-parasite interaction between the potato tuber rot nematode (Ditylenchus destructor), stem nematode (Ditylenchus dipsaci) and potato

ZUSAMMENFASSUNG Nematoden rufen weltweit erhebliche Verluste in der Kartoffelproduktion hervor. Der Knollenfäule-Nematode Ditylenchus destructor Thorne 1945 und das Stock-und Stangelälchen Ditylenchus dipsaci Kühn 1857 Filipjev, 1936, verursachen Läsionen an der Kartoffelknolle, was deren Qualität und Marktwert verringert. Diese Nematoden sind aufgrund ihres umfangreichen Wirtspflanzenspektrums schwierig zu kontrollieren und werden daher in vielen Ländern als Quarantäne-Nematoden geführt. In der hier vorliegenden Doktorarbeit wurden Experimente durchgeführt, um die Wechselwirkung von Kartoffel mit jeder dieser beiden Nematodenarten zu untersuchen. Verschiedene Populationen von D. destructor und D. dipsaci wurden molekular und morphometrisch charakterisiert. Die Gensequenz kodierend für die Untereinheit I der Cytochrom Oxidase (COI) auf der mitochondrialen DNA (mtDNA) wurde analysiert, um eine phylogenetische Beziehung zwischen den untersuchten Populationen darzustellen. Die Ergebnisse zeigten zwei deutlich getrennte Cluster für die D. destructor und die D. dipsaci Populationen. Eine Diskriminanzanalyse der morphometrischen Daten von Männchen und Weibchen von D. destructor und D. dipsaci Populationen verdeutlichte, dass diese beiden Arten mittels a-ratio und ihrem Durchmesser unterschieden werden können. Die sich ergänzende Kombination von molekularen und morphometrischen Untersuchungen ermöglichte die Identifikation der untersuchten Arten. Es wurden zwei Gewächshausexperimente mit 25 angebauten Kartoffelsorten durchgeführt, um diese auf Resistenz und Toleranz gegenüber Nematoden zu testen. Dazu wurde ein Standard-Screening Protokoll entwickelt. Resistenz und Toleranz wurden gemäß der derzeitigen Definition (Nematologie) bewertet. Die relative Anfälligkeit und äußere Verletzung der Kartoffelknolle stellten sich als beste Parameter für die Beurteilung der Resistenz respektive der Toleranz heraus. Alle 25 untersuchten Kartoffelsorten waren weder resistent noch tolerant gegenüber D. destructor oder D. dipsaci. Jedoch wurden Unterschiede in der Toleranz der Sorten festgestellt. Im Vorfeld zum Pflanzenexperiment wurden die Populationsdichten von D. destructor und D. dipsaci und deren Einfluss auf Ertragsverlust untersucht. Die initiale Populationsdichte hatte einen signifikanten Effekt auf den Schaden an der Kartoffelknolle und den Fortpflanzungsfaktor der Nematoden unter Gewächshausbedingungen. D. destructor verursachte Schäden bereits bei einer geringeren initialen Populationsdichte als D. dipsaci. Unter Klimakammerbedingungen wurde gezeigt, dass die Temperatur Einfluss auf die Schadensrate von D. destructor und D. dipsaci an Kartoffelknollen nimmt. Im Gegensatz zu einer Temperatur von 16°C waren 26°C sowohl optimal für die Vermehrung von D. destructor als auch für D. dipsaci. Obwohl für D. destructor und D. dipsaci unterschiedliche Temperaturanforderungen beschrieben wurden, verursachten beide Arten in ähnlichen Temperaturbereichen äußere Verletzungen an der Kartoffelknolle. Beauveria bassiana ist ein weltweit verbreiteter Pilz, der vor allem zur Bekämpfung von Insektenschädlingen in der Kartoffelproduktion Anwendung findet. Doppelbefall von Kartoffeln mit B. bassiana Sporensuspensionen im Boden mit D. destructor oder D. dipsaci begünstigte die Nematoden, was zu einer erhöhten Nematodenfortpflanzung und Knollenbeschädigung führte. B. bassiana allein war nicht schädlich für die Kartoffel. Es wurde vermutet, dass B. bassiana eine indirekte Rolle in der Wechselwirkung Nematode-Kartoffel spielt. Vorschläge für zukünftige Experimente werden angebracht, die einen weiteren Beitrag zu den hier vorgestellten Studien leisten können

Nematodes of forage legumes and grasses: Catalogue and Bibliography 1961- 1985

Se presentan 1 catalogo y 1 bibliografia sobre investigaciones relacionadas con el efecto de nematodos en gramineas y leguminosas forrajeras. En la seccion de catalogo, se incluyen nombres cientificos de plantas forrajeras (gramineas y leguminosas), nombres cientificos de nematodos asociados con ellas, pais donde se registro o se estudio el nematodo y no. de registro bibliografico. La bibliografia esta compuesta por 840 referencias bibliograficas (la mayoria con resumen) de trabajos de investigacion sobre nematodos y un listado de 308 referencias bibliograficas de registros unicos de asociaciones entre plantas y nematodos. (CIAT

Management of the stem and bulb nematode (Ditylenchus spp.) in winter beans (Vicia faba L) using biofumigant Brassica spp. and other allelopathic cover crops

Stem nematodes, Ditylenchus gigas and D. dipsaci, are major pests in field bean (Vicia faba L.) production in the UK. Currently, there are no recommended management measures for their control in V. faba production. A potential sustainable solution that has been used successfully for other plant parasitic nematodes is biofumigation using brassica cover crops. The active ingredient in biofumigant brassicas are isothiocyanates (ITC), which are produced from glucosinolates after disruption of brassica tissues. ITC have an affinity for proteins and can therefore cause mass disruption of the functional systems within target pests including nematodes. It is believed that concentrations of 50 μg/ml ITC are achievable in biofumigated soils. In vitro studies with allyl ITC identified that 50-100 μg/ml of 2-phenethyl ITC and benzyl ITC caused up to 100% mortality against the two stem nematodes after 24 h exposure whilst sulforaphane had no effect. Experiments to understand the effect of sub-lethal ITC concentrations were developed by exposing stem nematodes to doses of 3-100 μg/ml. In a 23% pluronic gel, stem nematodes were examined for their ability to move to the roots of their host, V. faba. The ITC affected the stem nematodes form by stimulating them to coil while limiting their foraging activities at sub-lethal (12.5-25 μg/ml) concentrations. At 25 μg/ml, 2-phenethyl ITC and benzyl ITC reduced migration towards the host by over 90% while sulforaphane had no effect on the stem nematodes’ ability to find their host even at 100 μg/ml. Brassica species were investigated under controlled conditions to determine whether they are non-hosts or hosts of stem nematodes. Three separate experiments were conducted for five brassica plants. The results showed that all brassica plants tested were poor hosts for D. gigas while certain brassica plant such as Sinapis alba and Eruca sativa can support the reproduction of D. dipsaci. Brassica plants that are associated with nematotoxic isothiocyanates were investigated for their suppressive effect in two field experiments. Brassica-legume mixtures and brassica grown alone were considered in field experiment 1, while field experiment 2 investigated the effect of three brassica species. The biomass of these brassicas was low in field experiment 1 because of a delayed sowing date and absence of N and S fertilizers although brassica plants grown in a mixture with legumes produced significantly greater biomass than brassicas sown alone. Field experiment 2 showed that brassica plants such as Brassica juncea, B. carinata and Sinapis alba could suppress Ditylenchus gigas compared to a fallow control. In conclusion, this study has demonstrated the potential of using brassica cover crops against Ditylenchus spp. in V. faba production

Nematodes

Nematodes are microscopic, eel-like roundworms that can infect humans, animals, and plants and cause serious damage and yield losses in a wide range of crops worldwide. This book includes thirteen chapters that address such topics as diagnosing nematode infections in crops (fruits and horticultural crops), management and biological control of plant-parasitic nematodes, biological indicators of nematodes, and entomopathogenic and marine nematodes. This comprehensive volume is a useful resource for students, teachers, researchers, field workers, and all those interested in and working with nematodes

Plant Parasitic Nematodes

Plant-parasitic nematodes (PPNs) are economically important pests for numerous agriculture and forestry crops, representing a significant constraint on global food security and forestry health. Root knot nematodes (Meloidogyne spp.), potato cyst nematodes (Globodera spp.), and root lesion nematodes (Pratylenchus spp.) are some examples of PPNs that are ranked at the top in the list of the most economically and scientifically important species. Current approaches to controlling these PPNs include the use of nematicides, but many pose serious concerns for human health and the environment. To cope with such threats, accurate diagnostic methods for nematode detection and a deep understanding of nematode infection processes, as well as of their intricate relationships with the host plants, are crucial for the development of effective integrated nematode management programs. This Special Issue entitled “Pant Parasitic Nematodes” is a collection of 11 original papers that cover a wide range of topics, including the state of the art of important PPN, and the detection and management of PPNs through sustainable and eco-friendly strategies

Characterising putative parasitism genes for root lesion nematodes and their use in RNA interference studies

Root lesion nematodes (RLNs, Pratylenchus spp.) are economically important migratory endoparasitic pests of crop plants. The overall aim of the work in this thesis was to undertake molecular studies on Pratylenchus thornei to characterise genes potentially involved in plant parasitism, and to determine if they are amenable to gene silencing (RNA interference). The recent availability of the transcriptomes of three RLN species, Pratylenchus coffeae, P. thornei and P. zeae significantly expanded the resources available for this study. Amongst the transcriptome data, putative parasitism genes (PPGs) were identified. A common assembly platform was also used to analyse transcriptome data to determine whether differences between PPGs identified here and those reported previously were consistent when the same assembly was used. Bioinformatic analysis was also undertaken to compare PPGs between different Pratylenchus spp. The results showed that there were some differences in the PPGs identified in P. coffeae, P. thornei and P. zeae. From the transcriptome of P. thornei, genes encoding potential protein or peptide effectors were identified and three aspects of plant parasitism were studied – cell wall modifying proteins (CWMPs) needed to overcome the physical barrier of cell walls in host plant roots, proteins required for detoxification of reactive oxygen species produced as a host defence response, and those thought to have other roles in parasitism. There was no information available on whether RLNs would take up dsRNA by ‘soaking’, and so conditions for optimisation of dsRNA uptake were established using P. thornei and P. zeae. Using these conditions, down-regulation of target genes in P. thornei by RNAi was studied. Mixed stage populations of nematodes of P. thornei and P. zeae were induced to ingest dsRNA when incubated in a basic soaking solution (M9 buffer, 0.05 % gelatine, 3 mM spermidine) in the presence of the 10-50 mM neurostimulant octopamine, 0.1-1.0 mg/mL FITC, and 0.5-6 mM spermidine for 16h. Under these conditions, nematodes vitality was not affected. Knockdown of pat-10 and unc-87 genes of P. thornei and P. zeae resulted in aberrant movement in both species, more so in P. thornei. A greater reduction of transcript expression of both genes in P. thornei also indicates that it may be more susceptible to RNAi than P. zeae. P. thornei treated with dsRNA of pat-10 and unc-87 have reduced replication in mini carrot discs, showing an 81 % and 77 % decrease in numbers of nematodes harvested after 5 weeks culture following RNAi. Hairy roots generated with constructs containing Ptpat-10 also resulted in significant decrease in P. thornei reproduction. Additionally, dsRNA constructs of either nematode species elicited RNAi effects in both species indicating a possible cross-species control of nematodes via RNAi. After soaking mixed stages of P. thornei in dsRNA for 16 hr and transfer to carrot mini-discs for 5 weeks, down-regulation of genes encoding CWMPs significantly decreased nematode reproduction by between 86-95%, respectively, showing that secretion of cellulase, pectate lyase and polygalacturonase are required for P. thornei to infect host plants effectively. Similarly, reproduction of P. thornei was also reduced when RNAi was initiated against cathepsins, fatty acid and retinol binding protein, peroxiredoxin, transthyretin-like protein and venom allergen-like protein (46-88%, respectively). However, RNAi did not reduce replication of P. thornei when RNAi was directed against galectin and thioredoxin. These results show that RLNs are amenable to RNAi, and indicate that the efficiency of RNAi-based gene silencing can differ depending on the target gene chosen, whether it is a member of a multi-gene family, the specific sequence chosen and also details of experimental treatments. This research described here also contributes to describing genes needed for entry into and migration in host roots and evading host defences. However, genes encoding effectors required by sedentary endoparasitic nematodes for feeding site formation were not found in RLNs