Cyst nematodes may refer to: Cactodera, a genus that includes the cactus cyst nematode, Cactodera cacti; Globodera, or potato cyst nematode, a genus of.
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He graduated as an agricultural engineer from Ghent University and obtained a PhD at the same University on the spread of plant-parasitic nematodes and their management in hydroponic cropping systems.
Soybean cyst nematode disease
Within the framework of the Belgian Cooperation, he worked from to as a researcher in crop protection, including nematology, at two research stations in Tunisia. There, he expanded the research in plant nematology over various areas covering molecular characterization, biology of host-parasite relationships, biological control, resistance and other forms of non-chemical control. He was appointed head of the Crop Protection Department in and became Director of Research in In , he was elected Fellow of the Society of Nematologists USA for outstanding contributions to Nematology; in the same year he was elected Fellow of the European Society of Nematologists for outstanding contribution to the science of Nematology.
He supervised 27 PhD students, who are active in nematology all over the world. He is past-president of the European Society of Nematologists He co-edited Root-knot Nematodes and the first and second editions of the text book, Plant Nematology. He is author or co-author of ten book chapters and refereed reviews and over refereed research papers. He is a member of the editorial board of the Russian Journal of Nematology. Perry - Roland N. His research interests centred primarily on plant-parasitic nematodes, especially focusing on nematode hatching, sensory perception, behaviour and survival physiology, and several of his past PhD and post-doctoral students are currently involved in nematology research.
He remained at Rothamsted until , when he moved to the Department of Biological and Environmental Sciences, University of Hertfordshire. He is author or co-author of over 40 book chapters and refereed reviews and over refereed research papers. He co-edits the book series Nematology Monographs and Perspectives. SCN adults are sexually dimorphic, meaning that they are dissimilar in appearance.
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The females are swollen and sedentary, and the males are vermiform worm-shaped and motile. Only the swollen female stage on the surface of soybean roots can be seen with the naked eye — the male and juvenile stages must be extracted from soil or plant roots and viewed under a microscope. The overall body shape of the nematode is determined by the pressure of its internal body fluids pushing against its strong, but flexible, outer "cuticle" like a water balloon. The outside of the cuticle has a series of fine rings annulations , like an accordion, that allows the cuticle to bend at any point along the nematode's body.
The cuticle is composed mainly of the structural protein collagen, and the cuticle is molted four times to allow growth and maturation of the nematode. The "head" of the nematode can be recognized by the presence of a short, dark spear with basal knobs the "stylet" just inside the tip of the head Figure 6. The stylet is hollow like a hypodermic needle and protrudes from the head when used by the nematode for feeding from plant cells and penetrating plant tissues.
Cyst Nematodes
The very outer tip of the nematode head above the stylet called the "lip" region is slightly elevated, rounded, and darkened in J2 of SCN. In a relatively clear area just below the stylet, a round, muscular pumping organ called the metacorpus can be seen - the metacorpus pumps substances i. Just below the metacorpus is another relatively translucent area that contains three esophageal glands that overlap the nematode's intestine on the ventral stomach side of its body.
The intestine can be recognized as a fairly long, dark area extending from the esophageal glands to the tail of the nematode. The tail of SCN J2 tapers uniformly to a fine, rounded tip that is hyaline clear. Adult females of SCN are the most easily diagnosed stage for this species. The female's stylet is slender with knobs that project slightly backward. The vulva and anus collectively form a cone-shaped projection from the rear of the female's body, giving them a characteristic "lemon" shape. The SCN females swell and molt through the juvenile life stages until they protrude from the plant roots see Disease Cycle.
The adult females of SCN are initially white on the root surface , and their heads are buried within the root for feeding. As the female ages, she turns yellow and eventually brown as she dies. Her body becomes a protective cyst encasing the eggs. Adult males of SCN are worm-shaped and relatively long Figure 7b , compared to second-stage juveniles. Although the head, stylet, and esophagus are similar to second-stage juveniles, the tail is short with a blunt, rounded terminus.
An easy, defining characteristic of males is the presence of two dark hooks called "spicules" that are always present at the opening of the testis near the tail. Like all nematodes, the soybean cyst nematode SCN has six life stages - egg, four juvenile stages J1-J4 , and the adult stage. The duration of the SCN life cycle runs from weeks, but this may be influenced by environmental conditions mainly adequate temperature and moisture.
Cyst nematode
Depending upon the environment, several generations of SCN can be completed in a typical soybean growing season. After embryonic development within the egg to the first-stage juvenile, the nematode goes through four molts to the adult stage. The molt to second-stage juvenile J2 occurs within the eggshell Figure 8 , and it is the J2 that emerges from the egg. Egg hatch seems to have evolved as a survival strategy in SCN. A low percentage of SCN eggs appear to hatch spontaneously -- it has been suggested that these eggs are the ones that are laid in a gelatinous matrix outside the female body.
A significant proportion of eggs that are retained within cysts are in a dormant state -- they do not hatch until soybeans are planted for the next growing season. It is hypothesized that exudates from soybean roots provide the hatching signals for dormant SCN. Another proportion of eggs within cysts do not hatch, even when conditions are favorable - they are in a state termed diapause. Diapause appears to be a time-mediated hatching process, the basis of which is not presently understood. The J2 is the infective stage of SCN.
The J2 migrates in soil and penetrates plant roots completely, usually just behind the root tip Figure 9. The J2 moves intracellularly to the root vascular tissue, often leaving a zone of visible root necrosis along their migratory path within the root.
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The J2 uses thrusts of its stylet and secretes cell-wall-degrading enzymes cellulases to migrate directly through plant cells Figure When the J2 reaches the root vascular tissue, nematode stylet secretions modify selected plant cells into an elaborate feeding site called a syncytium Figure The J2 will not continue development unless a syncytium is formed for feeding.
The syncytium is a large, metabolically active feeding site that becomes multinucleate as neighboring plant cells are incorporated into the syncytium by cell wall dissolution and cell fusion. The J2 feeds from the syncytium and begins to swell and become immobile Figure The subsequent juvenile stages molt and continue to enlarge as the nematode feeds. Approximately half of the juveniles will become swollen females, and the majority of the female body except for the head breaks through the root surface and becomes visible on the surface of the root Figures 13, Males develop coiled within the swollen J4 cuticle Figure 15 , and they emerge from the cuticle and root as motile, vermiform adult nematodes Figure 7.
Symptoms and Signs
It has been documented that a higher percentage of males is produced when the nematodes or host plants are under stress. Males do not feed, but they are required for sexual reproduction copulation with females that are exposed on the root surface. After fertilization, the majority of the eggs produced by the female are retained within its body, but some eggs may be laid in a gelatinous matrix extruded from the posterior vulva of the female. As the gravid female dies, its cuticle becomes a brown, hardened structure the cyst that encases and protects hundreds of viable eggs Figure Cysts often fall from roots and remain free in the soil.
As with many plant-parasitic nematodes in soil, soybean cyst nematodes do not move far from the root zone that they currently infest. In most cases, the natural migration of SCN within a field is defined as "contagious" — small patches of infested areas that gradually enlarge to encompass significant areas of disease.
Diseased areas become much more pronounced in sections of soybean fields that are under environmental stress i. The eggs may hatch when conditions in the soil are favorable, the larvae developing inside the cyst and the biological cycle repeating itself. There are usually three generations in the year. In the autumn or in unfavorable conditions, the cysts containing dormant larvae may remain intact in the soil for several years. The aboveground symptoms of SCN infection are not unique to SCN infection, and could be confused with nutrient deficiency, particularly iron deficiency, stress from drought, herbicide injury or another disease.
The first signs of infection are groups of plants with yellowing leaves that have stunted growth. The pathogen may also be difficult to detect on the roots, since stunted roots are also a common symptom of stress or plant disease. Observation of adult females and cysts on the roots is the only accurate way to detect and diagnose SCN infection in the field. Cultural practices, such as crop rotation and the use of resistant cultivars, are used to limit the damage due to SCN.
Because SCN is an obligate parasite requires a living host , a crop rotation involving non-host plants can decrease the population of SCN and has been shown to be an effective management tool. Plants that are already stressed are more susceptiable to infection, so good cultural practices, like maintaining soil fertility, pH and moisture can reduce the severity of infection.
Chemical control with nematicides is not normally used because the economic and environmental costs are prohibitive.
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