Parasitic Nematodes A:l 



CYST NH'-UTODra (ifOTWODEHA SPP.) 



The genus Heterodera was placed in the family Heteroderidae of the Tylen- 

 choidea by Thorne (19U9) with the genus Meloidogyne (root-knot nematodes). 

 Prior to 19U9j species of both these genera were placed in the genus Hete- 

 rodera . Prior to 19U0, there was a strong tendency to refer all of the 

 cyst-fonaing nematodes to a single s pecies, H. schachtii Schmidt, 1871, 

 though some effort was made to differentiate races, strains, or varieties 

 according to the host plants attached. However, little was done toward 

 study of morphology, and identification was difficult unless the host 

 plants were known. Some progress has been made in recent years, though 

 the situation is yet far from satisfactory. 



Morphology 



The adult females and cysts of Heterodera are the forms most cormonly 

 encountered. Adult females or cysts will be found on roots of various 

 plants if these are carefully removed from the soil and washed. The nema- 

 todes are attached to the roots by the neck only, with most of the body 

 outside the root. The females are white or yellowish in life, and the 

 cysts are light to dark brown. Average size is about 0.5mm by 0.75mm. 

 Some species are lemon-shaped, others are pear-shaped. Cysts are very 

 highly resistant to decay and may be found in soil in which infected 

 plants have grown, even many years afterward. 



The males are slender worms shaped very much like Meloidogyne males. That 

 is, they are about 1.25 to 1.75itoti long, slender (a = 35-UO), taper slight- 

 ly anteriorly, and have a short rounded tail (Goodey, 1951, K.g. 70). 

 Males will be found in abundance at certain times of the year, but mey he 

 very scarce at other times. The larvae have an average length of about 

 0.5mj'i. They differ from root-knot nematode larvae in that the stylet is 

 20 to 30 microns long ( Meloidogyne , 10-11 microns) and in the shape of the 

 anterior end. 



Excellent drawings of the larvae and other stages of H. schachtii will be 



found in "The Life History and Morphology of the Sugar-Beet Nematode, 



Heterodera schachtii Schmidt," by D. J. Haski (Phytopath. U0(2): 135-152, 



1950) . Larvae are seldom found free in soil, but can easily be obtained 



from the cysts. 



t 



The cysts are important contaminants of imported plant material and also 

 are searched for in soil in connection with quarantine and rotation pro- 

 grams in various countries. Consequently, they have benn intensively 

 studied, and most of the present information on identification of species 

 is based on characters of the mature cysts and their contents. 



A key to aid in identification of cysts is presented. Key characters will 

 be found on the mature cysts. 



