| Progress in the transfer of resistance to bunt (Tilletia
Caries, and T. foetida) from Agropyron to wheat*
C. F. KONZAK and R. E. HEINER Agronomy Departnent, Washington State University, Pullman, Washington, U.S.A. The transfer of a chromosome responsible for bunt resistance from A. elongatum 2n=70 to T. compactum variety Elgin, 2n=42, was completed by F. C. Elliott. This was accomplished through a number of backcrosses of the resistant hybrid to the variety Elgin. Numerous lines resistant to bunt have been selected by the present workers. Cytological examination has revealed that all resistant lines carry 44 chromosomes. Certain resistant lines, however, appeared to have 42 normal chromosomes, and a pair that are about half the size of normal chromosomes. These may be isochromosomes of the segment carrying the bunt resistance, and should greatly facilitate transfer of the desired genetic element to the standard variety. All lines carrying 42 chromosomes, when tested in the field, proved to be susceptible, indicating that no substitution lines, as yet have been observed. The Elgin backcross lines that contain the 42+2 isochromosomes appear to be superior to the 44 chromosome lines as far as visible agronomic merit is concerned. We may thus logically assume that the isochromosomes are identical with one of the arms of the Agropyron chromosomes in the 44 chromosome lines, but the possible inferiority of the 44 lines stems from the fact that the other arm contains genes responsible for undesirable characters. The isochromosomes can be readily identified both in mitotic and meiotic cells. Certain lines show some cytological instability, and as a consequence, instability in their bunt resistance. However, other lines appear to be quite stable both in chromosome behavior and bunt resistance. At present we are attempting to induce, by x-rays, a transfer of a segment carrying the resistance to a normal chromosome of Elgin. This can best be accomplished by using lines promising the 42+2 complement. |
| (* Journal note, Washington Agricultural Experiment Stations. Work was conducted project 966, in cooperation with the Washington State Department of Agriculture.) |