AN ASSESSMENT OF THE POTENTIAL OF 4DS.4DL-4S(L)L TRANSLOCATION LINES AS A MEANS OF ELIMINATING TALL OFF TYPES IN SEMIDWARF WHEAT-VARIETIES

Wheat varieties tend to be chromosomally unstable producing on average 2-3% of plants with abnormal chromosome numbers. A number of semi dwa rf wheat varieties, carrying the gibberellic acid insensitive dwarfing genes Rht1 or Rht2, have been seen to produce distinct tall off types due to reduction in dosage of the chromosome carrying the dwarfing ge ne. The UK variety 'Brigand', carrying Rht2 on chromosome 4D, produced very distinct tall off types when this chromosome was reduced in dosa ge. The frequency of tall off types was sufficiently high to cause the variety to fail United Kingdom statutory uniformity tests. An attempt to prevent the loss of chromosome 4D was made by constructing translo cation chromosomes involving the short arm of chromosome 4D, which car ries Rht2, and the long arm of chromosome 4S(l) from Aegilops sharonen sis, which carries a gene(s) conferring preferential transmission. The work in this paper describes the field evaluation of two lines carryi ng 4DS.4DL-4S(l)L translocations, and demonstrates their success in pr eventing spontaneously occurring monosomy of chromsome 4D in semi-dwar f wheats.