Urs Wyss

Feeding behaviour and pathogenicity of Xiphinema index on grapevine roots.

The feeding behaviour of Xiphinema index on grapevine roots in agar was studied with different observation chambers. The nematodes fed on excised roots preferring the zone of elongation of growing rootlets, then just emerging rootlets, callus tissue developing from cuts, wounds, and, last, slightly lignified tissue. The cell wall is perforated by a twisting action of the nematodes odontostyle. Soon after perforation, rhythmical contractions of the basal oesophageal bulb occur at a rate of about 70 contractions per 30 sec. On each contraction the bulb is stretched and the oesophageal lumen is dilated. Upon muscular relaxation the bulb shortens again and the lumen narrows from front to back thus forcing food into the intestine. Pumping is usually intermittent. The length of the period nematodes stay at one feeding site can vary from several minutes to several days. Root areas already fed on strongly attract the nematodes so that crowding often results at single sites. Attacked roots turn brown and swell at the tips. Epidermal and outer cortical cells collapse at feeding sites and show necrosis. In growing roots multinucleate cells, which are considerably enlarged and contain dense cytoplasm, are formed beneath the layer of necrotic cells. The development and significance of these modified cells is not yet clear.

Feeding of Tylenchorhynchus Dubius

The feeding of Tylenchorhynchus dubius on epidermal cells and root hairs of seedling roots of Brassica rapa var. silvestris was studied and analysed with the aid of cine film. The cell wall was punctured by rapid and characteristically irregular stylet thrusts. During salivation salivary granules flowed continuously from the site of synthesis in front of the dorsal gland-cell nucleus, through the gland duct towards the gland reservoir. Inside the cell a clear zone developed around the stylet tip and cytoplasm then accumulated there. The median bulb muscles contracted spasmodically, but uncoordinatedly so that the metacorporeal lumen was not dilated. At the onset of ingestion the forward flow of salivary granules through the duct was stopped by pump pulsations which soon became steady and very fast. Cytoplasm continued to accumulate around the clear zone in the food cell. Granular constituents of the cytoplasm were never seen to be drawn into the stylet. The accumulated cytoplasmic mass was never completely removed. After the nematodes departure this mass started to coagulate first. Cyclosis slowed down and finally stopped. Parasitized root hairs stopped growing. A comparison is made between the feeding of T. dubius and Trichodorus similis on the same host species.

Root and Cell Response To Feeding By Xiphinema Index

Feeding was observed and examined on seedlings of Ficus carica and Lycopersicon esculentum under gnotobiotic conditions in agar culture. Growing roots of fig seedlings were usually first attacked in the zone of elongation. The tips of such roots progressively swelled and developed into proliferating galls when feeding was continued for several days. Galled root-tips remained strongly attractive to feeding nematodes. About 1.0 μm thin sections through such galls revealed multinucleate and hypertrophied cells beneath and between necrotic cells at feeding sites. These modified cells, induced under aseptic conditions, were orientated to feeding sites. They were filled with cytoplasm and contained agglomerations of hypertrophied, lobed, nuclei with enlarged nucleoli. In serial sections up to 25 nuclei were counted in one single hypertrophied cell. This multinucleate condition appeared to arise from repeated mitoses without cytokinesis. In older cells signs of cell wall dissolution were quite common. Empty multinucleate cells adjacent to undamaged cells indicated that they were probably directly parasitized by feeding nematodes. The possible function of the modified cells is dicussed. Their induction appears to be a precondition for a successful host-parasite relationship. Single females produced many eggs when feeding on galled root-tips of fig seedlings. Egg production was, however, not induced when feeding was confined to root-tips of tomato seedlings which responded only with a slight swelling. Sections through parasitized tomato root-tips showed only necrotic cell reactions at feeding sites.

Feeding Phases of Xiphinema Index and Associated Processes in the Feeding Apparatus

Feeding mechanisms in Xiphinema index were observed, filmed and later analysed with the aid of cine film evaluation facilities. All the studies were made with X. index feeding on root tips of Ficus carica seedlings on agar culture in special observation chambers. Emphasis was placed on the events of a complete feeding cycle which is composed of distinct phases. Feeding sites are explored by lip contact only. The odontophore rotates during cell wall perforation by the odontostyle, but rotation is absent when the odontostyle is thrust rapidly through the contents of perforated cells. The odontostyle is usually inserted three to four cells deep before X. index starts feeding. Feeding behaviour after odontostyle protraction is characterized by a short phase (average 18s) with a definite sequence of events such as basal bulb elongation, depletion of gland ducts, shortening of the bulb and subsequent initiation of ingestion. Ingestion of food is achieved by the rapid pumping action of the basal bulb and is typically intermittent. Periods of continuous bulb pulsation alternate with short periods of pumping quiescence during which the bulb shortens and the gland ducts narrow from back to front, forcing fluids through them and also through the short duct that opens into the oesophageal lumen. It is possible that X. index releases salivary fluids into perforated cells during the short phase of prolonged bulb elongation just after odontostyle penetration and probably also during the brief ingestion pauses.

Zur Toleranz Wandernder Wurzelnematoden Gegenüber Zunehmender Austrocknung Des Bodens Und Hohen Osmotischen Drücken

Die Toleranz wandernder Wurzelnematoden gegenuber zunehmender Austrocknung des Bodens und hohen osmotischen Drucken wurde untersucht. Tylenchida erwiesen sich gegenuber beiden Bedingungen als weniger empfindlich als Dorylaimida. Die hochste Toleranz zeigte die in der obersten Bodenschicht lebende Art Tylenchorhynchus dubius, wahrend die in den tieferen Zonen vorkommenden Trichodorus-Arten am empfindlichsten waren. Die Untersuchungen zeigten, dass die unterschiedliche Toleranz nicht allein auf dem Wasserverlust beruht, den die Nematoden auf Grund des hoheren osmotischen Druckes der Aussenlosung erleiden.

Der Mechanismus Der Nahrungsaufnahme Bei Trichodorus Similis

Der Saugvorgang von Trichodorus similis an Epidermiszellen und Wurzelhaaren von Brassica rapa var. silvestris wurde in speziellen Beobachtungskammern bei sehr starker Vergroserung beobachtet. Ein kompletter Saugvorgang dauert nur wenige Minuten. Er setzt sich aus funf Phasen zusammen. Wahrend der Speichelabgabe, der langsten Phase, sammelt sich an der Einstichstelle Cytoplasma an. Dieses wird bei der Nahrungsaufnahme innerhalb kurzer Zeit aufgesaugt. Der Mundstachel wird kontinuierlich vor- und zuruckgezogen, sehr schnell beim Anstechen, langsamer bei der Speichelabgabe und wieder schneller bei der Nahrungsaufnahme. In der Mundhohle bildet sich ein Saugrohr, das in der Einstichstelle fest verankert bleibt. Das Zusammenwirken von Pharynx- und Osophagusmuskulatur wurde mit Hilfe der Filmtechnik analysiert. Die Funktion der Pharynxwandung als zusatzliche Pumpvorrichtung wird diskutiert.

Ultrastructure and Function of the Anterior Feeding Apparatus in Mononchus Aquaticus

The structure and function of the anterior feeding apparatus of Mononchus aquaticus, a predatory nematode, were studied by electron microscopic and cinematographic analysis. The lip region is composed of cuticular material and bears two sets of outgrowths, the liplets, projecting into the vestibulum. The buccal capsule, described here as a functional unit, is composed of three sets of plates. Ontogenetically, however, the anterior oblique plates belong to the cheilostome. Two sets of eight modified somatic muscles, the labial and stomatal muscles, are present at the level of the buccal capsule. During attack on the prey the lip region is pulled backwards by contraction of the labial muscles, and the anterior part of the buccal capsule, thus brought into close contact with the preys cuticle, is dilated. Simultaneously the oesophageal muscles contract, creating suction. During ingestion the posterior oblique plates of the buccal capsule are drawn backwards into a vertical position and the oesophageal lumen becomes fully dilated. The structure of the lumen lining of the anterior oesophagus suggests a sequence of two phases of dilation necessitated by the bulky meal. The stomatal muscles probably provide a good hold for the buccal capsule on the struggling of the prey. Further they may restore the head region to its original shape after feeding, thus acting as retractors. Marginal muscles of the oesophagus are well developed and are thought to assist in the closure of the complex oesophageal lumen lining. The structure of the anterior feeding apparatus in M. aquaticus is compared with that of the Dorylaimoidea.

Untersuchungen Zur Populationsdynamik Von Longidorus Elongatus

Im Freiland spielten sich an Erdbeerkulturen die starksten Populationsbewegungen von L. elongatus in der Zone der Hauptwurzelmasse ab. Eine Vertikalwanderung wurde auch unter ungunstigen Witterungsbedingungen nicht festgestellt. Die Beschrankung des Vorkommens gravider Weibchen auf die Fruhsommermonate zeigte, dass in Niedersachsen eine jahreszeitlich bedingte Vermehrungsrhythmik vorliegt. Die Entwicklungsgeschwindigkeit von L. elongatus stieg mit zunehmender Temperatur. Bei einer konstanten Temperatur von 30°C vollzog sich an Samlingen von Monatserdbeeren der Zyklus von der Eiablage bis zum erwachsenen Tier innerhalb von 9 Wochen. Bei 10° wurde keine Weiterentwicklung festgestellt. Die Toleranz gegenuber Gefriertemperaturen im Boden wurde durch einen hohen Wassergehalt des Bodens negativ beeinflusst. Um den Gefrierpunkt wechselnde Temperaturen wirkten weniger schadigend als eine konstante Frosteinwirkung.

Gnotobiology of Cyst Nematodes - Its Potential in Basic Research

The significance of gnotobiology, that is the study of a single species in the absence of others or in the presence of only known species, was reviewed for phytonematology by Zuckerman (1971). As early as 72 years ago Berliner and Busch (1914) tried to cultivate a cyst nematode (Heterodera schachtii Schmidt) on seedling roots in agar, but Widdowson et al. (1958) were probably the first to observe the development of such a nematode (Globodera rostochiensis (Woll. Behr.)) in sterile root culture. Now it has become a common practice to cultivate members of the Heteroderinae (which comprise the cyst-forming genera) under gnotobiotic conditions on roots in agar medium. Lauritis et al. (1983b) list the species of cyst nematodes so far successfully maintained in monoxenic culture.

Parasitierungsvorgang Und Pathogenität Wandernder Wurzelnematoden an Fragaria Vesca Var. Semperflorens

Parasitierungsvorgang und Folge des Parasitismus der an Erdbeeren haufig vorkommenden Nematoden-Arten Pratylenchus penetrans, Rotylenchus robustus, Tylenchorhynchus dubius und Longidorus elongatus wurden an Samlingen von Monatserdbeeren in Wasseragarkultur beobachtet. Unter aseptischen Bedingungen wurde durch den Massenparasitismus von P. penetrans das Cortexgewebe stark zerstort. P. penetrans war jedoch an dieser Pflanze nicht pathogen. Von den ektoparasitisch lebenden Wurzelnematoden erwies sich L. elongatus im Gegensatz zu R. robustus und T. dubius als ausserordentlich pathogen. Die Saugtatigkeit von L. elongatus wurde beobachtet und die Reaktion der Wurzelspitze auf den Parasitismus beschrieben. Durch L. elongatus parasitierte Erdbeerpflanzen zeigen charakteristische Wurzeldeformationen und starke Wachstumshemmungen. An Hand von Infektionsversuchen wurde nachgewiesen, dass das im Freiland festgestellte Schadbild eindeutig durch den Parasitismus dieser Art hervorgerufen wird. Zu einem gleichartigen Symptom fuhrte auch ein Befall durch Longidorus attenuatus.