| Studies on the nature and the possible origin of the
spontaneously translocated 1B-1R chromosome in wheat1)
D. METTIN, W.D. BLUTHNER, M. WEINRICH Martin-Luther-Universitat Halle-wittenberg, Sektion Pflanzenproduktion, Lehrstuhl fur Pflanzenzuchtung, 4104 Hohenthurm/Halle, DDR During the last years cytological investigations of a number of hexaploid wheat cultivars revealed the presence of rye chromosome 1R or, at least, parts of it. This alien chromosome substitutes for wheat chromosome 1B (ZELLER and FISCHBECK 1971; BLUTHNER 1972; ZELLER 1972; ZELLER and SASTROSUMARJO 1972; METTIN et al. 1973; ZELLER 1973). It could be demonstrated that almost all of these wheat lines took their origin as derivatives from experimental wheat-rye hybrids bred at Weihenstephan and Salzmunde. The only exception so far being the variety 'Salmon' which derived from a Triticale source in Japan (TSUNEWAKI 1964). Because of its fairly good transmission this particular rye chromosome, which provides resistance against rusts and mildew, has been transferred unconsciously by conventional breeding into an increasing number of mostly Europaen wheats. Previous crossing experiments had already given clear evidence for the existence of two types of spontaneous rye chromosome transfer, i.e. the 1R(1B) whole chromosome substitution and, what is called the 1B-1R translocation. While the presence of the complete chromosome 1R in the substitution lines has been confirmed by the Giemsa banding technique, there are some discrepancies regarding the nature of the IB-1R translocation (BENNETT and SMITH 1975; FRIEBE 1976; METTIN et al. 1976; MUNZER 1977; JORDANSKY et al.1978). Further research was thus needed for several reasons. Compiling all cytological data so far available it is evident that cultivars having the 1B-1R translocation are at least as frequent as the 1R(1B) substitution (Table 1). Phytopathological and electrophoretical studies reveal the presence of even more lines (HYZA 1978; SLOVENCIKOVA et al. 1978), though cytological checks are still lacking. There is, moreover, some indication that translocations are prevailing against substitutions in the breeders' material. Based on these findings it can be suggested that this particular type of rye introgression might occur also during the development of secondary Triticale via substitutional polyploidy. The interachange status of chromosome 1B-1R has been deduced from meiotic pairing with both chromosomes 1B and 1R resp. (ZELLER and SASTROSUMARJO 1972; BLUTHENER and METTIN 1973; ZELLER 1973). These data suggested the break point being located near or at the centromere, so that the translocated chromosome contains at least the major part of the short arm of 1R. Additional evidence has been achieved by using the Giemsa banding technique. While the short arm of chromosome 1B-1R of the translocation lines listed in Table 1 is characterized by the very distinct terminal band together with a subterminal intercalary C-band, the pattern for the long arm is somewhat conflicting, at least in one line. Wheat chromosome 1B has, according to GILI and KIMBER (1974), a medium-sized C-band at the end of the long arm, while the telomeric band on the long arm of 1R is very pronounced. The terminal band on the long arm of the interchange chromosome 1B-1R was found to be wheat-like by most of the authors (BENNETT and SMITH 1975; FRIEBE 1976; JORDANSKY et al. 1978). However, MUNZER (1977) observed a telomeric band being indistinguishable from the appropriate rye band, and suggested thus an intercalary translocation. A re-investigation of most of the translocation lines listed in Table 1 under comparable conditions revealed a medium-sized C-band at the end of the long arm, similar to wheat. Thus, on the basis of the banding pattern as well as the differences in arm length we confirm FRIEBE's results. |
| 1) Paper presented at the XIV. ICG, Moscow 1978, Contributed Paper session C 27 |
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