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.

The KL system in wheat permits homoeologous crossing over between closely related chromosomes

The Chinese wheat landrace Kaixianluohanmai(KL)expresses the ph-like phenotype.A major QTL,QPh.sicau-3A(syn.phKL),responsible for this effect has been mapped to chromosome arm 3AL.This study presents some characteristics of homoeologous pairing and recombination induced by phKL.In KL haploids,the level of homoeologous pairing was elevated relative to Ph1 Chinese Spring(CS)haploids.There was a clear preference for A–D pairing and less frequent for A–B and B–D,reflecting the higher levels of affinity between genomes A and D in wheat.The characteristics of pairing were affected by temperature and magnesium ion supplementation.The suitability of phKL for chromosome engineering was tested on three pairs of homoeologues:2Sv-2B,2Sv-2D,and 2RL-2BL.The recombination rates were 1.68%,0.17%,and 0%,respectively.The phKL locus in KL induced a moderate level of homoeologous chromosome pairing and recombination when the Ph1 locus of wheat was present,both in wheat haploids and hexaploids.The Ph1-imposed criteria for chromosome pairing and crossing over were relaxed to some degree,permitting homoeologous crossing over but only between closely related chromosomes;there was no crossing over between more differentiated chromosomes.Therefore,the phKL system(QPh.sicau-3A)can be a useful tool in chromosome engineering of wheat to transfer genes from closely related species with the benefit of reduced genomic chaos generated by the ph1b mutation.

Identification of an AP2 gene related to open flowering in diploid wheat(Triticum monococcum)

Cleistogamy involves the shedding of pollen within an enclosed flower. In barley, this trait is determined by the presence of a recessive allele at the gene Clyl, a member of the AP2 gene family. Here we show that the Clyl ortholog in einkorn （diploid） wheat （Triticum monococcum） TmAP2 shares a similar structure and identical pattern of transcription as Clyl. The transcript abundance of TmAP2 was high in the spike around the time of anthesis, but low in the leaf, plumule and radicle. The TmAP2 transcript was cleaved at its miR172 target site. Flower gaping at anthesis in einkorn wheat is induced by the expansion of the lodicules.

渗入杂交与小麦杂种优势

杂种优势利用是实现小麦增产稳产的重要途径.渗入杂交为小麦杂种优势利用提供了发展动力.小麦具有大量可渗入利用的近缘属种,同时基因组结构有利于外源基因渗入.目前常用的基因渗入有两种方式.一是借助染色体工程,通过不同基因组之间的部分同源染色体重组,将单个外源染色体区段以易位系为载体的方式渗入.易位系在引入外源染色体区段的同时,丢失了对应的小麦染色体区段,因此在常规育种中应用受限.但当其应用于杂交小麦,既保留了外源区段的优良基因,也不存在小麦基因缺失问题.二是通过同源染色体遗传重组,将不同染色体区段上的基因同时渗入,可实现小麦基因组遗传结构的重塑.小麦基因组缓冲性强,单个基因拷贝变化常常仅有较小的遗传效应,但多个基因的同时导入可能产生明显效果.因此,从基因组的角度丰富小麦遗传变异对杂种优势利用尤为重要.小麦3个亚基因组的遗传多样性不对称,其中D基因组的遗传多样性远低于A和B.因此,将未参与小麦进化的节节麦亚种的遗传多样性导入小麦,尽快丰富小麦D基因组的遗传多样性,是当前同源渗入的优先任务.