Icon RS 2015

After  the  first  reports on  spontaneous  wheat-rye chromosome substitutions 5R(5A) by Katterman (1937), O'Mara (1946) and Riley and Chapman (1958), during the past three decades  particularly, 1R(1B) substitutions and 1RS.1BL translocations were described in more  than 650  cultivars  of wheat  from all over  the  world (Blüthner  and  Mettin 1973; Mettin et al.  1973;  Zeller  1972; Zeller  1973;  Zeller and Fischbeck 1971). Even recent surveys show that sometimes more than 45 % of breeding material may contain those translocations (Zhou et al. 2007, Tahir et al. 2014) or 55% of CIMMYT bread wheat germplasm. In Hungary 53% of wheat cultivars registered during the last twenty years carry the 1RS translocation (Hoffmann 2008) This translocation has been deemed so important that it has been incorporated into >60 wheat varieties, including the prominent “Veery” spring wheat lines, that occupy >50% of all developing country wheat area, almost 40 million hectares.

Breeding programs are also interested in bread-making quality of wheat. They have not been able to benefit from the 1RS.1BL translocation because of its undesirable associated traits for bread-making quality. The presence of the rye storage secalins encoded by the Sec-1 locus, henceforth referred to as the proximal region, is associated with dough stickiness. The loss of the wheat low molecular weight glutenins (encoded by the Glu-B3 locus) and possibly the linked gliadins (encoded by the Gli-B1 locus), henceforth referred to as the distal region, is associated with reduced dough strength. 

Figure 2: F1 hybrid of wheat-rye substitution “Orlando” x wheat-rye transolcation “Kavkaz” with 2 heteromorphic univalents (1R + 1RS.1BL) + 20 homomorphic bivalents, after C-banding (228)

To address these quality concerns, a recombinant wheat-rye chromosome was engineered using induced homeologous recombination. The newly engineered chromosome arm, henceforth referred to as 1RSww (for proximal and distal wheat segments) has two short homeologous inserts of wheat chromatin: one replaces a proximal segment of rye chromatin with the Sec-1 locus, and the other replaces a distal rye segment and introduces wheat storage protein loci Glu-B3 and Gli-B1. The wheat segments introgressed in the 1RSww line were selected using the closest available crossover points to the Glu-B3/Gli-B1 and Sec-1 loci to minimize the possibility of losing beneficial alleles from the rye chromatin.

Figure 2a: F1 hybrid of wheat-rye substitution “Orlando” x wheat-rye transolcation “Kavkaz” with 1 heteromorphic bivalent (1R + 1RS.1BL) showing incomplete homologous chromosome pairing along the long arms, after C-banding (228)

The origin of the alien chromosome was intensively discussed  by genetic and  historical reasons. It turned out that  basically four  sources   exist - two in Germany (it might be one source, see Schlegel and Korzun 1997, one in the USA and one in Japan. The variety 'Salmon' (1RS.1BL) is a representative of  the latter Tsunewaki 1964) and the variety 'Amigo' (1RS.1AL) is  a representative of the penultimate group Beronsky et al.  1991; The  et al. 1992, while almost all remaining cultivars  can  be traced  back to one or to the other German origin (Zeller  1973; Blüthner and Mettin 1977).

In 2014, Howell et al. (2014) decribed lines not carrying the distal wheat region (1RS and 1RSwr) showed significant improvements in grain yield and canopy water status compared to near isogenic lines carrying the distal wheat segment (1RSww and 1RSrw), indicating that the 1RS region replaced by the distal wheat segment carries the beneficial allele(s). NILs without the distal wheat segment also showed higher carbon isotope discrimination and increased stomatal conductance, suggesting that these plants had improved access to water.

In 2011, about 1.050 varieties carry the 1RS.1BL translocation, about 100 varieties the 1RS.1AL translocation, and about 30 varieties a 1R(1B) substituion (cf. database attached). Their  most  important phenotypic deviation from common wheat cultivars is the so-called wheat-rye resistance, i. e. the presence of wide-range resistance to  races  of powdery mildew and rusts (Bartos  and Bares  1971; Zeller 1973), which is linked with decreased breadmaking  quality (Zeller  et  al. 1982), good ecological adaptability  and yield performance Rajaram et al. 1983; Schlegel and Meinel 1994, Singh et al. 2008, Zhai et al. 2016).

In China, since the 1960s stem rust has been basically controlled, because the varieties with 1B.1R translocation that are widely used have still showed effective resistance to stem rust. Nevertheless, a new race Ug99 could be a potential threat even to Chinese wheat production because the 1B.1R translocation with Sr31 is highly susceptible to the race (Howel et al. 2014).

There  was  no doubt so far that the Japanese  and  the American derivatives differ from one another and from the German  sources. Although  on  two places of Germany - Salzmuende near  Halle/S (breeder:  Riebesel)  and  Weihenstephan  near Munich(breeder: Kattermann - wheat-rye crosses were already carried  out since the twenties and thirties and independent pedigrees  could  be fragmentally reconstructed  by the few  reports left  (Blüthner 1992),  some authors presumed only one German source (Lein 1975; Moonen and Zeven 1984; Schlegel and Korzun 1997).

For  breeding  programmes  additional  recombination  within  the translocated  1RS  arm  of rye and between  the  different  wheat genetic backgrounds is wished (Müller et al. 1991; Lutz et al. 1992). In order to prevent miscrossings and to review the  wheat-rye  introgressions  a second list of the of various  1RS  sources  was compiled including some passport data. Because of space limit the proof of the introgression and the characteristics of the varieties are not included in the presentation. They can be obtained from the author by request.

© by R. Schlegel 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

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A compendium of reciprocal translocation in wheat