Paras. Eil 



STM AND BULB NWIATODE (DITYLENCHUS SPP. ) 



This genus represents one of the major plant-parasitic groups and is 

 reported in association with many kinds of host plants and from many 

 countries. There are about 30 si'ecies described, the best known be- 

 ing Ditylenchus dipsaci . As perhaps is to be expected from a genus 

 with many species and having an extensive host range and wide geo- 

 graphic distribution, there exists difficiilty in the exact taxonomy 

 of the group. There has long been recognition of "races" and applica- 

 tion of existing host lists must take into consideration this matter 

 of our not presently being able to accurately distinguish between 

 certain closely related species on the basis of morphology. Mixed 

 infections are also known to occur and must be guarded against in host 

 range studies. The book by Filipjev and Stekhoven (I9UI) is a good 

 reference for this genus and gives a taxonomic key, descriptions of 

 the species, and considerable information regarding the biology and 

 control of the more important species. 



Symptoms of plant disease caused by these nematodes vary widely, depend- 

 ing upon the plant and nematode species involved. The diseased parts 

 of the plants may be the roots, leaves, stems, flowers, and seeds. In 

 the case of the teasle, the entire plant may be invaded by the nematode, 

 Ditylenchus dipsaci . More usually, only particular parts of the host 

 plants are involved, for example, the foliar parts of alfalfa or the 

 tubers of potatoes. Almost all row crop plants, forage plants, grains, 

 and many ornamentals and weeds have been reported as hosts for nema^ 

 todes of this genus. Some of the forms parasitic on higher plants can 

 be cultijred on fungi, and it is possible that all the species may be 

 incidental feeders on the surface of roots, whether or not they ever 

 become endoparasitic in habit. Members of the genus which are regarded 

 as parasites of known importance, for the most part, are foxind within 

 the diseased host tissues. 



Plants exhibiting irregularity of growth form and distortions of foliar 

 parts should be checked for the presence of Ditylenchus . Lesions of 

 stems and iinderground parts of plants showing a loose, granular, brown- 

 colored condition of the cells should also be checked carefully for 

 these nematodes which are likely to be located in advance of the lesions. 

 A galled condition of the roots similar to root-knot is also known to 

 occur on some plants as a result of invasion by Ditylehchus . The damage 

 caused by these nematodes is by chemical in addition to mechnaical 

 action, as evidenced by what appears to be dissolution of the middle 

 lamella of the hosts' cells and abnormal hypertrophy of cells and tis- 

 sues in the vicinity of the nematodes. 



Some members of this genus have the ability to withstand adverse envi- 

 ronmental conditions by going into a state of dormancy called anabiosis . 

 This capacity for survival under a wide range of circumstances is a 

 matter of significance in dissemination and control of such nematodes. 



