HYBRID CHLOROSIS IN INTERSPECIFIC CROSSES OF OENOTHERA: POLYGENIC INHERITANCE OF THE NUCLEAR COMPONENT
Interspecific hybrids between Oenothera hookeri or O. elata and O. argillicola are severely chlorotic and die as seedlings because the chloroplasts of either species are unable to function in the presence of the chromosome complex inherited from the other (Stubbe, 1959; Stinson, 1960). In the present investigation the chromosome complex of O. argillicola was genetically partitioned into a number of small sets of chromosomes by means of backcrosses, and the chlorosis-inducing potential of these sets on chloroplasts of O. hookeri and O. elata was determined. The chlorosis-inducing potential of sets of O. hookeri and O. elata chromosomes on the chloroplasts of O. argillicola was determined in a parallel series of crosses.In both series the results indicated that the nuclear component of hybrid chlororis was polygenic. No individual foreign chromosome produced an observable degree of chlorosis while various combinations produced various degrees of chlorosis. In general, the level of the chlorosis paralleled the number of foreign chromosomes in the hybrid, the F-1 hybrid in each case being the most severely affected.