Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2004
Publication Date: November 1, 2004
Citation: Xu, S.S., Friesen, T.L., Mujeeb-Kazi, A. 2004. Seedling resistance to tan spot and Stagonospora nodorum blotch in synthetic hexaploid wheats. Crop Science. Vol. 44:2238-2245. Interpretive Summary: Synthetic hexaploid wheats (synthetics) are developed by combining the AB genomes from tetraploid wheats and D genome from goat-grass Aegilops tauschii. Synthetic hexaploid wheats have the same chromosome constitutions as bread wheat and the desirable genes in synthetics can be directly transferred into bread wheat by conventional breeding approaches. The Wide Hybridization Program at the International Maize and Wheat Improvement Center (CIMMYT) recently developed two sets of elite synthetics. The systematic characterization of the important traits in these synthetics will be very useful for wheat breeders and geneticists to effectively exploit the synthetics in certain breeding and genetic research programs. Thus far, some important traits such as agronomic performance, quality traits, and resistance to various diseases have been evaluated. However, their resistance to tan spot and Stagonospora nodorum blotch (SNB) has not yet been evaluated. Tan spot and SNB are important foliar diseases of bread wheat and durum wheat. These two diseases have ability to cause serious yield losses. Because the majority of current bread and durum wheat cultivars are susceptible, there is a need to find new sources of high level resistance to tan spot and SNB and transfer the resistance to local cultivars. In this study, we evaluated 120 elite CIMMYT synthetics and their durum wheat parents for seedling resistance to the two diseases. The data showed that 56 (46.7%) and 36 (30.0%) synthetics were resistant to tan spot and SNB, respectively, whereas resistance was almost absent in the durum parents. The results suggest that the elite CYMMYT synthetics are an excellent source of new resistance to tan spot and SNB. The data from this study provides additional guides for selections of parental lines in developing new resistant cultivars and mapping populations.
Technical Abstract: Production of synthetic hexaploid wheat (SHW or synthetic) lines (2n = 6x = 42, AABBDD) is a practical way to generate a useful germplasm source for the transfer of desirable traits from Aegilops tauschii Coss. and tetraploid wheat (Triticum turgidum L.) to bread wheat (T. aestivum L.). The Wild Hybridization Program at the International Maize and Wheat Improvement Center (CIMMYT) recently selected and characterized two sets of elite SHW lines (Elite 95 and Elite 2). The objective of this study was to evaluate the SWH lines for their seedling resistance to tan spot [Pyrenophora tritici-repentis (Died.) Drechs.] and Stagonospora nodorum blotch (SNB) [Stagonospora nodorum (Berk.)]. In this study, 120 elite CIMMYT SHW lines and their durum wheat (T. turgidum L. var. durum) parents were inoculated with P. tritici-repentis race 1 and a standard field isolate of S. nodorum, respectively, in two separate three-replication experiments. The seedling reactions to P. tritici-repentis and S. nodorum were evaluated 7 and 10 d post-inoculation, respectively. The plant leaves were also infiltrated with the host selective toxin Ptr ToxA at the two-leaf stage and sensitivity was evaluated 3-4 d post infiltration. As expected, most SHW lines were the same as their durum parents in their sensitivity to Ptr ToxA because the sensitivity locus Tsn1 is located on chromosome 5B. However, a few of the synthetics were different from their durum parents, suggesting that heterozygosity and heterogeneity might exist in some of the SHW lines and durum parents. The toxin sensitivity significantly increased susceptibility of the synthetics to tan spot but had no significant effects on durum parents. The data showed that 56 (46.7%) and 36 (30.0%) SHW lines were resistant to tan spot and SNB, respectively, whereas resistance was almost absent in the durum parents. These results suggest that the elite CYMMYT synthetics are an excellent source of new resistance to tan spot and SNB and should be useful in developing new resistant cultivars and adapted germplasm in bread wheat.