The height-reducing gene
Rht8 was introduced into Italian wheats by breeder Nazareno Strampelli from the Japanese landrace Akakomugi, and has been widely
used in wheats adapted to southern and eastern European conditions. Following identification of a close linkage to
Rht8, microsatellite marker
Gwm261 has been used extensively to screen large numbers of diverse international germplasm. A 192bp allele at this locus has been
taken as “diagnostic” for
Rht8 and used to infer the international distribution of
Rht8. In this paper, we report several instances of cultivars and mapping populations that vary for the presence of the 192bp
allele at the
Xgwm261 locus (
Xgwm261
192
), but with no associated reduction in height, suggesting a lack of association with
Rht8. For instance, in the population derived from a cross between Sunco (
Rht-B1b,
Xgwm261
165
) and Tasman (
Rht-D1b,
Xgwm261
192
), there were significant height differences associated with the segregation of
Rht-B1b and
Rht-D1b, but no height differences between
Xgwm261 genotypes. Similar results were obtained in a population derived from the cross between Molineux (
Rht-B1b,
Xgwm261
192
) and Trident (
Rht-D1b Xgwm261
208
). In contrast, the cross between Trident and Chuanmai 18 (
Xgwm261
192
) gave significant height effects at both the
Rht-D1 and
Xgwm261 loci, with no epistatic interaction between loci. Chuanmai 18 is closely related to the Strampelli wheat Mara (ancestrally
derived from Akakomugi) and is therefore likely to carry
Rht8. The old Japanese cultivar Norin 10, used by Norman Borlaug to introduce
Rht-B1b and
Rht-D1b into Mexican wheats, also has a 192bp allele at the
Xgwm261 locus, and the sequence of the amplified product is identical to that of Akakomugi. We suggest that the widespread use of
Norin 10-derived germplasm during and after the Green Revolution introduced a second haplotype into international germplasm,
in which
Xgwm261
192
has no association with
Rht8. Therefore, the presence of
Xgwm261
192
is only indicative of
Rht8 in wheat cultivars that have inherited this allele from Akakomugi or a Strampelli wheat ancestor.
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