Genetic diversity among synthetic hexaploid wheat accessions (Triticum aestivum) with resistance to several fungal diseases

Synthetic hexaploid wheat (SHW) is known to be an excellent vehicle for transferring large genetic variations especially the many useful traits present in the D genome of Aegilops tauschii Coss. (2n = 2x = 14, DD) for improvement of cultivated wheat ( Triticum aestivum L., 2n = 6x = 42, AABBDD). The objectives of the present study were to (1) evaluate genetic diversity among 32 selected SHW accessions with resistance to several fungal diseases using Amplified Fragment Length Polymorphism (AFLP) and Simple Sequence Repeat (SSR) markers and (2) identify diverse SHWs for pyramiding genes conferring resistance to different diseases. These SHWs containing different accessional sources of the D genome were identified from about 1000 SHW accessions developed by the Wheat Wide Crosses program at the International Maize and Wheat Improvement Center, Mexico. Of the 32 SHW accessions eight had resistance to Fusarium head blight ( Fusarium graminearum Schw.), seven were resistant to leaf rust ( Puccinia triticina Eriks.), eight resistant to Helminthosporium spot blotch [ Cochliobolus sativus (Ito et Kurib.) Drechsler ex Dastur (syn.: Bipolaris sorokiniana (Sacc.) Shoem., Helminthosporium sativum Pammel, King et Bakke)], seven resistant to Septoria tritici blotch ( Septoria tritici Roberge in Desmaz.), while two were resistant to both Fusarium head blight and leaf rust. Seventeen Eco RI/ Mse I AFLP primer combinations and 27 highly polymorphic SSR markers including 20 D genome specific markers were screened over all 32 SHW accessions. Among the 703 AFLP fragments scored, 225 were polymorphic across the 32 SHW accessions. Polymorphic information content (PIC) among the SHWs for AFLP ranged from 0.06 to 0.50 with an average PIC of 0.24. Major allelic frequency from SSR analysis ranged from 0.23 to 0.81 with an average of 0.45. Number of alleles per locus for the SSR markers ranged from 3 to 15 with an average allele number of 7.4. Average gene diversity and PIC for the SSR markers was 0.69 and 0.66, respectively, with the highest values being for the D genome specific markers. Cluster analysis showed distinct groups among the SHW accessions studied. Mantel statistics between the distance matrices from AFLP and SSR analyses showed a moderate but significant correlation (r = 0.52**). Our results indicate that the SHW accessions studied possess substantial genetic diversity and are valuable user-friendly pre-breeding materials for breeding improvement of wheat with resistan