STRUCTURAL ORGANIZATION OF AN ALIEN THINOPYRUM-INTERMEDIUM GROUP-7 CHROMOSOME IN US SOFT RED WINTER-WHEAT (TRITICUM-AESTIVUM L.)

Barley yellow dwarf virus (BYDV) resistance in soft red winter wheat ( SRWW) cultivars has been achieved by substituting a group 7 chromosome from Thinopyrum intermedium for chromosome 7D. To localize BYDV resis tance, a detailed molecular genetic analysis was done on the alien gro up 7 Th. intermedium chromosome to determine its structural organizati on. Triticeae group 7 RFLP markers and rye specific repetitive sequenc es used in the analysis showed that the alien chromosome in the P29 su bstitution line has distinguishing features. The 350-480 bp rye telome ric sequence family was present on the long arm as determined by South ern and fluorescence in situ hybridization. However, further analysis using a rye dispersed repetitive sequence indicated that this alien ch romosome does not contain introgressed segments from the rye genome. T he alien chromosome is homoeologous to wheat chromosomes 7A and 7D as determined by RFLP analysis. Presence of the waxy gene on chromosomes 7A, 7B, and 7D but its absence on the alien chromosome in P29 suggests some internal structural differences on the short arm between Th. int ermedium and wheat group 7 chromosomes. The identification of rye telo meric sequences on the alien Thinopyrum chromosome and the homoeology to wheat chromosomes 7A and 7D provide the necessary information and t ools to analyze smaller segments of the Thinopyrum chromosome and to l ocalize BYDV resistance in SRWW cultivars.