Development And Ldentification Of A Wheat-Tetraploid Thinopyrum Elongatum 6E/6D Substitution Line With Stripe Rust Resistance

Stripe rust ,caused by Puccinia striiformis f.sp.tritici,is one of the most devastating foliar diseases of common wheat worldwide.Breeding new wheat varieties with durable resistance is the most effective way of controlling the disease.The tetraploid Thinopyrum elongatum（2n=4x=28,EEEE）has excellent traits such as multiple flowers and seeds,excellent disease resistance（stripe rust,Fusarium head blight,and powdery mildew）,drought resistance,and cold tolerance,making it important germplasm for genetic improvement of wheat varieties.In this study,wheat-tetraploid Th.elongatum 6E/6D substitution line K17-1065-4 was identified by genomic in situ hybridization（GISH）and fluorescence in situ hybridization（FISH）in progenies of hybrids and self-cross between Triticum durum-tetraploid Th.elongatum partial double diploid 8801 and Sichuan wheat cultivars（Shumai 482 and Shumai 921）.Seedling and adult stage stripe rust resistance were identified and agronomic traits were evaluated among K17-1065-4 and its parents.The diploid Th.elongatum reference genome sequence was used to develop tetraploid Th.elongatum chromosome 6E specific molecular markers,and the validity of the obtained specific molecular markers was verified.The results are as follows:1.The GISH,FISH,and FISH painting results showed that K17-1065-4 contained 42chromosomes,in which the 6D chromosome pair of common wheat was replaced by 6E chromosomes of tetraploid Th.elongatum.Thus,K17-1065-4 was a wheat-tetraploid Th.elongatum 6E/6D substitution line.2.Stripe rust resistance identification revealed that SM482,SM921 and K17-1065-4were highly susceptible to stripe rust,whereas 8801 was highly resistant to stripe rust during seedling stage.At adult stage,SM482 and SM921 were highly susceptible to stripe rust,while 8801 and K17-1065-4 were highly resistant to stripe rust.3.Agronomic traits showed that the number of tillers,plant height and spike length of K17-1065-4 were similar to wheat parents SM482 and SM921,but the number of spike grains was significantly higher.The thousand grain weight in K17-1065-4 was lower than SM921,but similar as SM482 and significantly higher than 8801.4.In total,3,382 simple sequence repeats（SSRs）were 6E specific in diploid Th.elongatum.We randomly selected 60 SSR sequences and verified the specificity,the results showed that 33 SSR marker pairs could accurately track the tetraploid Th.elongatum 6E chromosome and 10 markers could be used to distinguish the E genome of Th.elongatum from other wheat relatives.5.Molecular markers,GISH and stripe rust resistance analysis were performed on 154F₂ individual plants obtained from the hybrids of K17-1065-4 and SM482.The progeny that could amplify specific bands were all highly resistant to wheat stripe rust,and GISH results confirmed that stripe rust resistance progenies contained intact alien chromosomes.In summary,we identified a high stripe rust resistance wheat-tetraploid Th.elongatum6E/6D substitution line K17-1065-4 with excellent agronomic traits,and developed chromosome chromosome-specific SSR markers for accurate tracking of alien 6E in common wheat background.This study will lay the theoretical foundation for mapping the stripe rust resistance gene and molecular marker assisted breeding in tetraploid Th.elongatum,and provide materials for breeding highly resistant,high yielding and high quality wheat.