Study of pentaploids N. tabacum­tabacum-glutinosa, revealed the following: a) The chromosomes behaved very regularly at meiosis, forming 24 N. tabacum pairs and 12 N. glutinosa univalents; non-conjunction of tobacco pairs was very rare and whether trivalents were formed at all could not be ascertained with certainty. The chances of achieving substitution in the pentaploid generation are therefore very poor. b) Of the 37 pentaploid plants sampled ten lacked a N. glutinosa chromosome (the sample was not random since selected plants of recessive phenotype had been included). Three plants lacked N. tabacum chromosomes and were substitution heterozygotes, Because of the appreciable chance for substitution the breeder should concentrate on amphidiploid generation. c) Segregation in N. tabacum × glutinosa amphidiploids observed in the past was found to be due in part to loss of chromosomes carrying dominant marker genes; differential affinity of chromosomes at meiosis is thus very pronounced. The cause of the greater meiotic irregularity of amphidiploids as compared with pentaploids has not been determined.

(Full article published with kind permission from "Tobacco International")