LINKAGE RELATIONSHIPS AMONG GENES ON WHEAT CHROMOSOME 5A THAT CONDITION RESISTANCE TO HESSIAN FLY

Hessian By [Mayetiola destructor (Say)] is a serious pest of wheat (Triticum ssp.) in many wheat growing areas of the world. A number of genes (H1-H26) that confer resistance to Hessian By have been described. The linkage relationships of many of these genes, which are useful in breeding wheat for resistance to Hessian By, are unknown. Testcross analyses were made in tetraploid durum wheat (Triticum turgidum L.) and tested to biotype D of Hessian fly to determine the linkage relationships among genes H9, H10, H12, H14, H15, H16 and H17, all conferring resistance to biotype D. Also, monosomic 5A plants of susceptible cultivar Chinese Spring were crossed as seed parents to Purdue wheat (T. aestivum L. em Thell.) lines carrying gene H10 or H12. Testcross analyses indicated that six of these genes appear to occupy a single Linkage block on wheat chromosome 5A in the order H9 to H15, H10, H17, H16, and H12. Gene H14 did not appear to be within the Linkage block H9 to H12. Additionally, F-2 plants derived from 41-chromosome F-1 plants and F-3 families derived from F-2 resistant plants were tested against biotype D. F-2 segregation deviated significantly from 3 resistant : 1 susceptible and h families from resistant F-2 plants deviated significantly from 1 resistant : 2 segregating for both crosses involving H10 and H12. Thus, monosomic analyses provided additional evidence that genes H10 and H12 are Likely on chromosome 5A. Linkage between these genes would not seriously Limit efforts to pyramid them in breeding for resistance to the Hessian By because the linkage values are more than 20 centimorgans.