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Abstract: Until the present, two separate disease conditions of mushrooms have been attributed to nematodes or eclworms. One of these is referred to in a book by Falconer (1898). Although impossible to determine from this account the nomas involved, it is considered likely that they and the disease described are similar or identical with a rot. disease of mushrooms (Steiner, 1933; Haseman and Ezell, 1934). In these cases a free-living nematode, Rhabditis lambdiensis Maupas, was found to be an indirect, but important factor as a carrier of the pathogen, Pseudomonas tolaasii Paine. This bacterium is rapidly spread by the nematode and causes the rot spots called "Bacterial Pits" and other disfigurations on the mushroom caps and stems. The second disease reported recently (Lambert tf al., 1949) as occurring in Pennsylvania and Delaware is one in which the nematodes are the direct cause of injury. The nematode involved is a spear or stylct-bcaring form ; a new species of Ditylenchus closely related to the important stem and bulb parasite, Ditylenchus dipsaci (Kuhn). This disease is confined to the hyphae or mycelia upon which the nematodes feed by means of a tiny, hollow buccal stylet. Certain symptoms can be associated with this spawn-destroying disease. First noted is a decline of production in spots at various locations. This reduction may be evident as late as the fourth break or flush, or as early as the first. In extreme cases the spawn will be nearly wiped out by heavy infections before the first break is over. The compost in diseased locations has a peculiar rotten odour and feels greasy. It is of particular interest that on the surface of the beds a growth of very fine light grey fungus is frequently found ; this has been identified (Lambert et al., 1949) as Arthrobotrys superba Corda and feeds upon nematodes that it traps in its meshes. In the last stages, the bed surface, conspicuously bare of mushrooms, settles an inch or so below the general level.
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