COMPENSATION INDEXES OF RADIATION-INDUCED WHEAT AGROPYRON-ELONGATUM TRANSLOCATIONS CONFERRING RESISTANCE TO LEAF RUST AND STEM RUST

Species belonging to the genus Agropyron are an important source of di sease resistance for bread wheat. Several resistance genes have been t ransferred. C-banding and in situ hybridization are the methods of cho ice for analyzing introgressed alien chromatin. Using these methods, w e characterized radiation-induced wheat-Agropyron elongatum chromosome translocation lines carrying the rust resistance genes Sr26 and Sr25/ Lr19. Data show that Sr26 is located on the translocation chromosome T 6AS.6AL-6Ae#1L. The Ag. elongatum segment in this translocation has a length of 2.48 mum. The Sr25/Lr19 genes in cultivar 'Agatha' are locat ed on a 2.55 mum long Ag. elongatum segment present in the translocati on chromosome T7DS.7DL-7Ae#1L. The wheat-Ag. elongatum. translocation chromosome present in the ethyl methanesulfonate (EMS) treated derivat ive 'Agatha-28' is similar to that present in Agatha. The Ag. elongatu m segment present in the EMS treated derivative 'Agatha-235' has a len gth of 1.99 mum and is inserted intercalary in the long arm of wheat c hromosome 7D, resulting in the translocation chromosome T7DS.7DL-7Ae#1 L-7DL. A compensation (CI) index was calculated as the ratio of the le ngth of the missing wheat segment as percent of the corresponding whea t arm divided by the length of the transferred alien segment as percen t of the corresponding alien chromosome arm. The CIs in T6AS-6AL-6Ae#1 L and T7DS-7DL-7Ae#1L are 1.15 and 0.95, respectively. These are close to the desirable value of 1 and indicate good compensation ability. T he CI in T7DS.7DL-7Ae#1L-7DL is 0.60 and indicates poor compensation a bility. This index may allow the prediction of the performance of any compensating wheat-alien chromosome translocation.