Paras. iiX 



STTT^ET- NEMATODES (TYLENCHORHYNCHUS SPP. ) 



The genus Tylenchorhynchug Cobb, 1913, is comprised of many species, 

 some of which are important plant pathogens, Thorne (19U9) places this 

 genus in the subfamily Tylenchinae, of the family Tylenchidae . Nematodes 

 of this genus are medium in-size ranging from .6 to 1.7 mm in length. 

 The cuticle is coarsely annulated and in at least one species, T. claytoni, 

 longitudinally subdivided (Morphology section, Plate I, Fig. U). Lateral 

 fields are marked by four to six incisures. The esophagus is of the 

 tylenchoid type with a well developed basal bulb connected with the 

 intestine by a large cardia. Females have double ovaries, outstretched, 

 with the vulva near the middle of the body. Female tail blunt, rounded. 

 Male tail slightly arcuate and enveloped by the bursa. 



At least two species, and undoubtedly there are others, have been shown 

 to cause considerable damage to crop plants. Reynolds _et. al. (1953) 

 have demonstrated that T. dubius can cause moderate stunting of cotton 

 under both greenhouse and field conditions. Steiner (1937) described 

 T. clay to ni from tobacco in South Carolina and at the time considered 

 it to be an apparently rare parasite of tobacco. Subsequent to that 

 time, Graham (195U) reports that T. claytoni was present in 67 per cent 

 of 175 soil samples collected from fields where tobacco jas stunted 

 (1951 through 1953). It was also found in cotton and corii samples. He 

 demonstrated its pathogencity on tobacco in both greenhouse and field 

 trials. Effects on tobacco are stunted top growth and a much retarded 

 root system. Graham fvirther reports (195U) that root lesions are absent 

 and root decay does not occur, although the roots are seriously retarded 

 in their growth and do not elongate normally. 



In North Carolina, T. claytoni is one of the most serious nematode para- 

 sites to tobacco and is widespread in the state, having been identified 

 from 27 counties. It apparently has a wide host range, although few 

 studies have been made to date to determine this. Aside from tobacco, 

 high populations have been found in soil samples from cotton, corn, mile, 

 alfalfa, strawberry, oats, soybeans, peanuts, and various ornamentals. 

 It appears to be primarily an ectoparasite. 



A monograph dealing with the taxonomy of the genus has been prepared by 

 Allen (1955). The key to the species known to that date is copied from 

 the monograph for inclusion with these Notes. At the present time, two 

 additional species have been described and are not included in the mono- 

 graph or key by Allen. These are as follows: 



Tylenchorhynchus martini Fielding, 1956. Resembles T. claytoni 

 Steiner, 1937, but differs in having simple body annulationsj 

 female tail blunt with distinctive, finger-like shape, that is, 

 having parallel outline instead of being tapered j and presence 

 of a slight constriction setting off the lip region. Males 

 absent . 



