Inheritance in Nicotiana tabacum XXVII. Pollen Killer, An alien genetic locus inducing abortion of microspores not carrying it

A cytogenetic study of experimental introgression from N. plumbaginifolia (pbg) into N. tabacum (tbc) has been pursued in this laboratory for several years
(CLAUSEN 1952). In the hybrid derivatives it was observed that genically controlled pollen abortion was associated with the addition of a pbg chromosome to the tbc complement. This chromosome also carried the locus (Bs) determining resistance or probably immunity to black shank, a serious disease of commercial tobacco caused by Phytophthora parasitica var. nicotianae. (For description see CLAYTON and AICAIVRTRY 1950). Paradoxically, it developed that the pbg chromosome under study produced its effect on gametophytes in which it was not present. Thus, the male gametophytes containing a complete set of 24 tbc chromosomes degenerate while most of the functional pollen had the constitution 24 tbc + 1 pbg.
This paper presents a description of the genetic aspects of the problem with some suggestions as to the possible method of action of the locus involved. Certain other phases of the larger investigation will be mentioned but only as they apply to the pollen lethal condition. The investigation was initiated by the late PROF. R. E. CLAUSEN who participated actively in the work presented here.