GENETIC-RELATIONSHIPS AMONG SOYBEAN PLANT INTRODUCTIONS WITH RESISTANCE TO SOYBEAN CYST NEMATODES

Soybean [Glycine max (L.) Merr.] cultivars in the USA, which are resis tant to soybean cyst nematode (SCN) (Heterodera glycines Ichinohe), ha ve resistance derived from only a few plant introductions (PIs). Many other SCN resistant PIs have been identified which could be used as so urces for broadening the diversity of resistance genes in cultivars. T he objectives of this research were to study the relationship among PI s with SCN resistance using restriction fragment length polymorphism ( RFLP) markers and to assess their resistance response to five races of H. glycines. Thirty-eight PIs previously reported as being resistant to one or more SCN races were evaluated for resistance to H. glycines Races 1, 2, 3, 5, and 14 in a greenhouse and were tested with 201 geno mic DNA clones. PI 437654 and PI 438489B were resistant to all five SC N races. Four PIs were resistant to four SCN races, nine resistant to three rates, four resistant to two races, four resistant to one race a nd the remainder had only moderate resistance or moderate susceptibili ty to one or more races. The PIs were polymorphic for 138 clones which revealed 301 polymorphic DNA fragments. The groupings of the Pls for both cluster analysis and principal component analysis (PCA) were asso ciated with resistance responses to races of H. glycines. One major gr oup of PIs was distant from all previously used sources of resistance. These PIs had only moderate resistance to Race 3 but could potentiall y provide new genes for resistance to this race. The other PIs were in groups that included PIs with resistance sources previously used by b reeders. This information on the relationship of the PIs should help r esearchers developing resistant soybean cultivars to identify sources of SCN resistance which are not closely related to previously used sou rces.