Aphelenchoides ritzemabosi

Aphelenchoides ritzemabosi (Black currant nematode, Chrysanthemum foliar nematode, Chrysanthemum leaf nematode, Chrysanthemum nematode, Chrysanthemum Foliar eelworm) is a plant pathogenic nematode. It was first scientifically described in 1890 in England. This nematode has a wide host range. Among the most important species affected are Chrysanthemums and strawberries. A. ritzemabosi is a migratory foliar feeding nematode. It can feed both ectoparasitically and endoparasitically, with the later causing the most significant damage. When adequate moisture is present, this nematode enters the leaves and feeds from inside the tissue. Typical damage is characterized by necrotic zones between the veins of the leaves. Its lifecycle is short; only ten days from egg to mature adult. A single female can lay as many as 3,500 eggs. This pest can be difficult to control. Host plant resistance, hot water treatments, and predatory mites are recommended. First described in England in 1890, it was given the name Aphelenchus olesistus by Ritzema-Bos in 1893. In 1908, Markinowski grouped A. olesisyus, A. fragariae, and A. omerodis under the common name A. omerodis. A. olesistus was recognized as an individual species and given the current name Aphelenchoides ritzemabosi by Schwartz in 1911.This species may also be known by the following synonyms: Aphelenchus ritzemabosi Schwartz 1911, Pathoaphelenchus ritzemabosi (Schwartz 1911), Steiner 1932, Aphelenchoides (Chitinoaphelenchus) ritzemabosi (Schwartz 1911) Fuchs 1937, Pseudaphelenchoides ritzemabosi (Schwartz 1911) Drozdovski 1967, Tylenchus ribes Taylor 1917, Aphelenchus ribes (Taylor 1917) Goodey 1932, Aphelenchoides ribes (Taylor 1917) Goodey 1933, Aphelenchus phyllophagus Stewart 1921 Aphelenchoides ritzemabosi ranges in length from 0.7 to 1.2 mm with the females of the species having the potential to be slightly longer than the males. Male A. ritzemabosi are often wider than females. The head is sharply differentiated from the body in that it is noticeably wider than the neck. This nematode has four lateral incisures. Females have at least two rows of oocytes and the spicule on the male nematodes is a short ventral process without outgrowths. A. ritezmabosi has a wide host range of almost 200 plant species, and is an important disease in chrysanthemum and other ornamentals. Other ornamental hosts of A. ritzemabosi are anemones, asters, carnations, Chinaster, cinerarias, coneflowers,crassulas, creeping bellflower, dahlias, delphiniums, elders, lupines, monkeyflower, phlox,pouchflower, rhododendrons, sages, Siberian wallflower, water peperomia, and zinnias.A common symptom of A. ritezmabosi is seen when the nematode is feeding in the foliar tissue. Angular lesions are formed, which are chlorotic at first then turn necrotic as the feeding persists. A sign that an A. ritzeambosi nematode is feeding in the bud of a plant is brown scars on the bud and surrounding tissue. The nematode also produces secretions that have the ability to cause several other symptoms in infested plants including shortening of inter-nodes, creating a bushy appearance, browning and failure of the shoot to grow, as well as distorted leaf formation. A. ritzemabosi is an endoparasitic nematode, meaning that it feeds on plant tissue from the inside of the cell. Adult nematodes infest the leaves of their host plant by swimming up the outside of the stem in a film of water. This can only happen when the relative humidity is very high.Once it has reached a leaf it enters through the stomata to begin feeding in an endoparasitic fashion. Once inside the host it is capable of invading and infecting host tissue at all life stages, other than the egg. The more mature stages show an improved ability to migrate through host tissue. When the growing season of the host comes to an end the nematode goes into a quiescent state overwintering inside the leaf tissue. When spring comes they end their quiescent state then find and infest a new host. A. ritzeambosi is also capable of feeding ectoparasitically, from the outside of the cell. It has been known to feed ectoparasitically on the buds of some plants such as strawberry and black currants. Above ground ectoparasitic feeding can only happen in events of prolonged high humidity or other circumstances providing a long term film of water on the plant which protects the nematode from exposure. Ectoparasitic feeding also happens on the roots in the soil.All of this happens in an extremely short amount of time, it takes around 10 days for A. ritzembosi to go from egg to adult. All life stages are vermiform and migratory. Studies have shown that in optimal conditions a single female A. ritzemabosi can produce up to thousands of offspring in the period of about a month. French & Barraclough (1961) obtained a maximum number of 3,500 progeny from a single A. ritzemabosi female after 38 days at mean greenhouse temperatures of 17° to 23 °C. Temperature influence on reproduction showed that higher temperatures generally lead to more reproductive actions. No reproduction was observed at temperatures of 8 degrees Celsius. Fertilized females go on reproducing for six months without further fertilization In chrysanthemum leaves, the female lays about 25-30 eggs in a compact group. These eggs hatch in 3–4 days and the juveniles take 9–10 days to reach maturity. The total life cycle takes 10–13 days In susceptible varieties of Chrysanthemum, the female remains in one place within the leaf as it feeds on adjacent cells and continuously lays eggs. In resistant varieties, the female moves through the leaf laying only a few eggs as it goes. Few, if any of the juveniles make it to maturity.Like many other plant parasitic nematodes, A. ritzemabosi has the ability to reproduce on fungal tissue, suggesting that soil fungus may contribute to the nematode's survival when no host is available. Laboratory tests have shown that Botrytis cinerea and many Rhizoctonia species of fungi are more conducive to A. ritzeambosi growth and reproduction. These fungi are used to culture and propagate other Aphelenchid species as well. In adult females, the eggs can be seen developing inside their bodies before they are deposited to hatch. If an adult female is cut off from a reliable supply of food it has been observed that the egg will disappear from view, evidently being aborted and reabsorbed by the female.