Fine mapping and characterization of stripe rust resistance gene YrAYH in near-isogenic lines derived from a cross involving wheat landrace Anyuehong

Stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is a devastating disease in wheat worldwide.Discovering and characterizing new resistance genes/QTL is crucial for wheat breeding programs.In this study,we fine-mapped and characterized a stripe rust resistance gene,YRAYH,on chromosome arm 5BL in the Chinese wheat landrace Anyuehong(AYH).Evaluations of stripe rust response to prevalent Chinese Pst races in near-isogenic lines derived from a cross of Anyuehong and Taichung 29 showed that YrAYH conferred a high level of resistance at all growth stages.Fine mapping using a large segregating population of 9748 plants,narrowed the YRAYH locus to a 3.7 Mb interval on chromosome arm 5BL that included 61 annotated genes.Transcriptome analysis of two NIL pairs identified 64 upregulated differentially expressed genes(DEGs)in the resistant NILs(NILs-R).Annotations indicated that many of these genes have roles in plant disease resistance pathways.Through a combined approach of fine-mapping and transcriptome sequencing,we identified a serine/threonine-protein kinase SRPK as a candidate gene underlying YrAYH.A unique 25 bp insertion was identified in the NILs-R compared to the NILs-S and previously published wheat genomes.An InDel marker was developed and co-segregated with YrAYH.Agronomic trait evaluation of the NILs suggested that YrAYH not only reduces the impact of stripe rust but was also associated with a gene that increases plant height and spike length.

Wheat breeding in the hometown of Chinese Spring

The common wheat landrace Chinese Spring(CS) was made famous by the work of Ernie Sears, a great cytogenetist, who developed a number of CS-based aneuploid series that were used to identify individual wheat chromosomes. Based on this, a standard karyotype and nomenclature system was developed for wheat chromosomes that allowed wheat researchers to analyze and manipulate the wheat genome with unprecedented precision and efficiency. Nevertheless, not much is known about the utilization of CS at its hometown, Chengdu in Sichuan province, during early wheat breeding activity. In this review, we follow the speculation that CS is a selection from the Cheng-du-guang-tou(CDGT) landrace. We provide a description of how CDGT became a founder landrace for wheat breeding activities in early times. We show that CDGT-derived varieties were reinforced genetically by crosses to six more exotic parents. These varieties remained the major elite cultivar for several decades. Later, synthetic hexaploid wheats were introduced into the breeding program, firstly using those from CIMMYT and later using materials produced with local tetraploid wheat and goat grass. Finally, we discuss the strategies and future directions to improve wheat yield and resistance through an expanded genetic basis,especially by recapturing lost genetic variations from landraces and related wild species, a process that may set an example for wheat breeders in China and elsewhere.