TowardstheMapBasedCloningofaRecessive Fusarium ResistanceDeterminantfromDiploid Medicago sativa

population. TheFusarium susceptible and resistant phenotypes of the individuals in an F2 segregation popula tion was inferred from a biological test using injured root test. The resulting phenotypes were used to position the Fusarium resistance determinant on linkage group 6 of the Medicago sativa genetic map. Using the DNA based molecular markers genome walk was initiated from both sides of the genetic region constructing two contigs which are about 0.5 centiMorgan (~500 kilobasepairs) apart. The introduction of this genetic determi nant into tetraploid alfalfa cultivars was unsuccessful since only triploid and pentaploid hybrids could be recov ered from the 4 #–2 # crosses. The isolation of the gene and establishment of the function of this recessive Fusarium determinant is under progress.