Production of wheat-Leymus racemosus translocation lines

Production of wheat-Leymus racemosus translocation lines

Masahiro Kishii

Kihara Institute for Biological Research, Yokohama City University,

Maioka-cho 641-12, Totsuka-ku, Yokohama 244-0813, Japan

E-mail: nkishii@yokohama-cu.ac.jp

Leymus racemosus (2n=28=NsNsXmXm) is a wild species belonging in Triticeae and has been known to have many interesting characters for wheat breeding including salt tolerance (McGuire and Dvorak 1981) and wheat scab (Fusarium Head Blight, FHB) resistance (Mujeeb-Kazi et al. 1983; Wang et al. 1986). Recently, it was found that it has biological nitrification inhibition activity that inhibits nitrification from NH₄⁺ to NO₃^- in soil (Subbarao et al. 2007), that would then reduce emission of N₂O global warming gas from nitrogen fertilizer and may be related to nitrogen use efficiency. The number of L. racemosus chromosome addition lines has been developed (Qi et al. 1997; Kishii et al. 2004), and evaluation of their characters has revealed that Lr#I, Lr#J, and Lr#n chromosomes possessed BNI activity (Subbarao et al. 2007). Lr#J and Lr#l chromosomes also had resistance gene(s) against leaf or stem rust, respectively (unpublished data). Lr#H chromosome addition line showed early heading (Kishii et al. 2004), and Lr#k line possessed novel storage protein (unpublished data). It is desirable to transfer these characters to wheat varieties. The traits of Lr#n chromosome has been already introduced to wheat by inducing Robertsonian (centromeric) translocation between wheat and Lr#n chromosome (Kishii et al. 2008). The purpose of the study is to produce centromeric translocation lines of other five L. racemosus chromosomes of Lr#H, Lr#I, Lr#J, Lr#k, and Lr#l.

Five L. racemosus chromosome disomic addition lines (DALr#H, DALr#I, DALr#J, DALr#k, and DALr#l) were produced in the previous publication (Kishii et al. 2004). To produce centromeric translocation lines, firstly the disomic addition line was crossed with wheat monosomic lines (cv. Chinese Spring background; 2n=41=AABBDD) (Fig. 1). Homoeology group of L. racemosus chromosomes had been roughly assigned by the previous RFLP analysis (Kishii et al. 2004; Table 1). In F1, the plants with 42 chromosomes were selected. The presence of L. racemosus chromosome and identification of wheat chromosomes was done by genomic in situ hybridization (GISH) and C-banding following the previous publication (Kishii et al. 2004). The translocations between wheat and L. racemosus chromosomes were identified in F2 by GISH.

By screening about 100 F2 plants for each cross, we could find translocations for all of five L. racemosus chromosomes (Fig. 2; Table 1). The frequency for obtaining translocation was different among the L. racemosus chromosomes. The highest frequency (3%) was observed in the short arm of Lr#H and the long arm of Lr#I translocation during the present study. The short arm translocation was easier to obtain comparing to the long arm one except for Lr#I chromosome. Total number of short arm translocation was double to that of the long arm. This trend was similar to the previous result for the production of Lr#n chromosome translocation lines (Table 1; Kishii et al. 2008). It may be possible to speculate that the larger chromosome fragment size of long arm has higher chance to possess negative factors that may affect transmission rate to progenies. It may be also affected by imperfect conservation of homology between wheat and L. racemosus chromosomes. As we could not have translocations of long arm in some L. racemosus chromosomes, it is necessary to increase the number for screening to obtain translocation in the future.

The translocation produced in this study could be utilized in breeding program after backcrossing them with elite wheat varieties and if there are few agronomically undesirable factors present in the translocations. Among the translocation lines, those of Lr#I and Lr#J would be particular interest, because these have BNI character (Subbarao et al. 2007). It is reported that the short arm of 7Lr#1 chromosome, which is homologous chromosome of Lr#J (Kishii et al. 2004), has novel FHB resistance gene, Fhb3 (Qi et al. 2007; Chen et al. 2005). It is generally difficult to do genetic analysis in translocation line of alien species, but it may be possible to do for Fhb3 if Lr#J is not FHB resistance.

References

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Kishii M, Ban T, Subbarao GV, Ortiz-Monasterio I (2008). Transferring of the biological nitrification inhibition (BNI) character from Leymus racemosus to wheat. In: Appels R, Eastwook R, Laguday E, Langridge P, Mackay M, McIntyre L, and Sharp P, eds. Proc 11th Int Wheat Genet Symp. Brisbane, Australia. Poster 017 (http://ses.library.usyd.edu.au/bitstream/2123/3426/1/P017.pdf).

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