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

Das, Modan K., Bai, Guihua, Mujeeb-Kazi, Abdul, Rajaram, Sanjaya
Genetic resources and crop evolution 2015 v.63 pp. 1285-1296
Aegilops tauschii, Fusarium head blight, Helminthosporium, Septoria, Triticum aestivum, alleles, amplified fragment length polymorphism, biotic stress, cluster analysis, corn, crossing, disease resistance, fungi, gene frequency, genetic resistance, genetic variation, hexaploidy, leaf rust, loci, microsatellite repeats, plant-incorporated protectants, synthetic products, transgenic plants, wheat, Mexico
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 (i) evaluate genetic diversity among 32 selected SHW with resistance to several fungal diseases using Amplified Fragment Length Polymorphism (AFLP) and Simple Sequence Repeat (SSR) markers and (ii) identify diverse SHW for pyramiding genes conferring resistance to different diseases. These SHW containing different accessional sources of the D genome were identified from about 1,000 SHW developed by the Wheat Wide Crosses program at the International Maize and Wheat Improvement Center (CIMMYT), Mexico. Ten SHW had resistance to Fusarium head blight, nine were resistant to leaf rust, eight resistant to Helminthosporium spot botch and seven resistant to Septoria biotic stresses. Two SHW were resistant to Fusarium head blight and leaf rust. Seventeen EcoRI/MseI AFLP primer combinations and 27 highly polymorphic SSR markers with 20 genome specific markers were screened over all 32 synthetics. Amongst the 703 AFLP fragments scored, 225 were polymorphic across the 32 SHW. Polymorphic information content (PIC) among the SHW for AFLPs 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 markers. Cluster analysis showed distinct groups among the wheat 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 studied possess substantial genetic diversity and are useful pre-breeding materials for improving wheat with resistance to Fusarium head blight, leaf rust, Helminthosporium spot blotch, and Septoria diseases. In this effort the most diverse SHW can be used for pyramiding resistance genes to different diseases.