II.5 Genetic background as a factor in influencing the expression of net blotch resistance.
W. J. R. Boyd and T. N. Khan, Department of Agronomy, The University of Western Australia, Nedlands, Western Australia 6009.
The Ethiopian variety C.I.5791 has proved resistant to all isolates of D. teres to which it has been tested, and under all conditions of testing. In contrast, the resistance of the Manchurian variety C.I.2330 is specific to certain isolates and subject to variability in expression, depending upon the conditions of testing. Dampier (C.I.13521) and Atlas (C.I.4118) represent susceptible varieties. In crosses between resistant and susceptible parents F1 host reaction is more resistant (more dominant) in those instances in which C.I.5791 is the resistant, or, when C.I.13521 is the susceptible, parent. This result was interpreted to indicate that these varieties possess a genetic background which promotes the penetrance and expressivity of the gene (s) governing resistance to net blotch (Khan, 1969). In order to confirm this hypothesis single plants of the cross (Dampier x Atlas) x C.I.5791 have been tested. With every plant heterozygous for the genetic complement of C.I.5791, segregation would be dependent upon segregation for "background" effects contributed by the susceptible varieties. Of the 76 plants examined, host reactions ranged from resistant (as expected from F1's of Dampier x C.I.5791) to moderately susceptible (as expected from Atlas x C.I.5791).
KHAN, T. N. (1969). Can. J. Genet. Cytol. 11:587-591.