SEPARATION OF 3 SPECIES OF DITYLENCHUS AND SOME HOST RACES OF D-DIPSACI BY RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM

This study examined the ribosomal cistron of Ditylenchus destructor, D . myceliophagus and seven host races of D. dipsaci from different geog raphic locations. The three species showed restriction fragment length polymorphisms (RFLPs) in the ribosomal cistron, the 18S rDNA gene, an d the ribosomal internal transcribed spacer (ITS). Southern blot analy sis with a 7.5-kb ribosomal cistron probe differentiated the five host races of D. dipsaci examined. Polymerase chain reaction (PCR) amplifi cation of the ITS, followed by digestion with some restriction endonuc leases (but not others), produced restriction fragments diagnostic of the giant race. Because the PCR product from D. myceliophagus and the host races of D. dipsaci was about 900 base pairs and the ITS size in D. destructor populations was 1,200 base pairs, mixtures of population s could be detected by PCR amplification. ITS fragments differentiated between D. dipsaci and Aphelenchoides rhyntium in mixed populations. This study establishes the feasibility of differentiation of the host races of D. dipsaci by probing Southern blots with the whole ribosomal cistron.