RESUMEN
On a survey of plant parasitic nematode fauna, belonging to the suborder Tylenchina, about 110 soil and root samples were collected from different sugar beet field in fars Province in Iran. The samples were washed and the nematodes were extracted by Centrifugal Flotation Technique according to the modified method by De Grisse, 1969. They were fixed and transferred to glycerine, then permanent slides were mounted. Morphological and morphometrical characters of collected species were carefully studied and the characters were compared with the original descriptions and differences were discussed. In this study 18 species belonging to 11 different genera of subordes Tylenchina were identified as follows. Boleodorus thylactus, Ditylenchus destructor, D. dipsaci Geocenamus brevidens, G. rugosus, Helicotylenchus digonicus, H. pseudorobustus, H. vulgaris, Heterodera filipjevi, H. schachtii, Pratylenchus neglectus, P. thornei, Psilenchus hilarulus, P. hilarus, Stictylus mucronatus, Tylenchorhynchus ventrosinatus, Tylenchus davainei and Zygotylenchus guevarai. The species of the genera Ditylenchus, Heterodera, Pratylenchus and Psilenchus were comparatively more distributed than the others. This investigation revealed that sugar beet cyst nematode (Heterodera schachti) was found already in most sugar beet fields in this Province. Fathabod, Marvdasht and Tasuj-kwar were the most infested areas. Cysts collected from 100 gr. Of soil samples were 120 to 121 in number and the eggs and second stage larvae in each gr. of soil were 104.1 to 104.5 respectively.