J'ary;;. . D:l 



RID AND LFAF Nl'llATODES (APIIELKf-ICtlOIDTsS SPP.) 



The genus Aphelenchoidos consists of numeroiis species, is widespread, 

 and specimens are frequently found in soil and plant samples. This 

 genus has a diversity of biological associations. There are species 

 that are parasitic on and in plant roots, buds, and leaves. Some 

 species feed on fungi and possibly on soil algae, others are parasites 

 or associates of insects, and still others are predators of nematodes 

 and other soil microorganisms. 



As the common name of this genus suggests, the plant parasitic species 

 of this group are probably best known because of the foliar diseases 

 they cause. Symptoms of disease vary, depending upon the host plant 

 and the nematode species Involved. Plants may show varying degrees of 

 deformation of stems, leaves, flowers, and buds may remain rudimentary. 

 "Dwarf" or "crimp" are descriptive terms applied to such conditions as, 

 for example, in strawberries. In chrysanthemums, dahlias, ferns, and 

 other plants leaves invaded by the nematodes show discolorations and 

 eventually necrotic areas appear, these spots are often bounded by the 

 larger leaf veins and appear as distinctly angular in outline. Aphelen- 

 choides may lodge in the leaf sheathes of grasses or between the devel- 

 oping leaves or petals in the buds. These nematodes feeding as ecto- 

 parasites, as they are not within the plant tissues, can cause symptoms 

 of disease in the parts noted, such as abnormal foliar color, distortion 

 of the leaves, and in some cases lead to decay of the structures. 



An important example of a disease caused by a species of Aphelenchoides , 

 in which the stem of the host is affected, is the red ring disease of 

 coconuts. The nematodes may initiate invasion of the host by penetrat- 

 ing at the terminal growing point, being carried there in some cases 

 by an insect. Eventually the entire parenchyma of the host is pene- 

 trated by the migrating nematodes, and a red-collored ring which char- 

 acterizes the disease is found in the parenchyma of the tree's trunk. 



It is not possible to assign a definite role to all of the Aphelen - 

 choides species that are recovered from about plants. The fact that 

 some of the plant-parasitic species can thrive on cultures of fungi 

 suggests parasitism on the higher plants may be only incidental or of 

 a facultative nature. It is possible that incidental feeding on the 

 root surfaces by some of the often quite numerous Aphelenchoides and 

 similar forms could be of importance. Numerous minute wounds in the 

 presence of other soil microorganisms may be related to establishment 

 of disease complexes. The ability of Aphenlenchoides to survive on 

 fungi and perhaps algae, plus an ability to withstand periods of inac- 

 tivation in conditions of adversity, must be considered when developing 

 control practices for this genus. 



The taxonomy of the genus is difficult, not because of a lack of reports 

 in the literature, but rather because of so many accounts without 



