Theor Appl Genet (1998) 96 : 1110—1120 ( Springer-Verlag 1998 A. J. Worland · V. Korzun · M. S. Ro ¨ der M. W. Ganal · C. N. Law Genetic analysis of the dwarfing gene Rht8 in wheat. Part II. The distribution and adaptive significance of allelic variants at the Rht8 locus of wheat as revealed by microsatellite screening Received: 17 October 1997/Accepted: 12 November 1997 Abstract Wheat microsatellite WMS 261 whose 192-bp allele has been shown to be diagnostic for the commer- cially important dwarfing gene Rht8 was used to screen over 100 wheat varieties to determine the worldwide spread of Rht8. The results showed Rht8 to be wide- spread in southern European wheats and to be present in many central European wheats including the Rus- sian varieties ‘Avrora’, ‘Bezostaya’ and ‘Kavkaz’. Rht8 appears to be of importance to South European wheats as alternative giberellic acid (GA)-insensitive dwarfing genes do not appear to be adapted to this environment. The very successful semi-dwarf varieties bred by CIM- MYT, Mexico, for distribution worldwide have been thought to carry Rht8 combined with GA-insensitive dwarfing genes. Additional height reduction would have been obtained from pleiotropic effects of the photoperiod-response gene Ppd1 that is essential to the adaptability of varieties bred for growing under short- winter days in tropical and sub-tropical areas. The microsatellite analysis showed that CIMMYT wheats lack Rht8 and carry a WMS 261 allelic variant of 165 bp that has been associated with promoting height. This presumably has adaptive significance in partly counteracting the effects of other dwarfing genes and preventing the plants being too short. Most UK, Ger- man and French wheats carry an allelic variant at the WMS 261 locus with 174 bp. This could be selected because of linkage with the recessive photoperiod-sen- sitive ppd1 allele that is thought to offer adaptive signif- icance northern European wheats. Communicated by G. Wenzel A. J. Worland ( ) · C. N. Law John Innes Centre, Cereals Research Department, Norwich, NR4 7UJ, UK Fax:#44 1603 502241 V. Korzun · M. S. Ro¨der · M. W. Ganal Institut fur Pflanzengenetik und Kulturpflanzenforschung (IPK), Corrensstr 3, D-06446, Gatersleben, Germany Key words Adaptability · Dwarfing gene (Rht8) · Microsatellite · Molecular markers · Wheat Introduction A semi-dwarf stature for wheat (¹riticum aestivum 2n"6x"42) has been shown to permit increased yields through more efficient utilisation of available assimilates (Ford et al. 1985) and by reducing yield losses associated with crop lodging (Dalrymple 1986). The very complex genetic control of plant height in wheat is determined by genes on many chromosomes (Law et al. 1973). To date 21 genes of major effect on plant height have been assigned Rht symbols in wheat (McIntosh et al. 1995). The major genes determining plant height are normally classified into two groups depending on their reaction to exogenous giberellic acid (GA) (Gale and Gregory 1977; Bo¨ rner et al. 1996). The GA-insensitive dwarfing genes of wheat are present in two homoeologous allelic series located on the short arms of chromosomes 4B1 and 4D (Gale et al. 1975; Gale and Marshall 1976; McVittie et al. 1978). GA- responsive dwarfing genes have been located on chro- mosomes 2A (Worland et al. 1980), 2DS (Worland and Law 1986), 7BS (Worland et al. 1990) and 5A (Sutka and Kovacs 1987). The height reductions determined by the wheat dwarfing genes can be further modulated by increasing the potency of alleles for height sup- pression (chromosome 4B1 and 4D, GA insensitive dwarfing genes, Rht12), reducing the potency of height- promoting alleles (Rht7, Rht8) or by shortening the life cycle (pleiotropic effects of Ppd1, Ppd2 or Ppd3). In bread wheat there is a general correlation between reduced height and reduced yield (Law et al. 1973). In 1 Nomenclature post-7th International Wheat Genetics Symposium, Cambridge, UK, 1988