Further Investigations on the Chromosome Number of Secale Cereale L

Abstract

Two new chromosome numbers, 9 and 10, were added in Secale cereale L. The extra chromosomes of these plants must represent the k-chromosome of the 8-chromosome rye. Such plants arose probably from 8-chromosome plants through duplication of the k-chromosome. These chromosomes form sometimes multivalent associations.
Such a chromosome multiplication disturbs the balance in the cell and weakens the viability of both, germ cells and zygotes, which accordingly show high sterility.
Crossings between the 7- and the 8-chromosome rye have been carried out. The F_I-plants had for the most part either 14 or 16 somatic chromosomes. The former number will be obtained when the two segments _??_ and _??_ reunite into the original chromosome _??_. The latter number will be easily produced through segmentation of the original chromosome into _??_ and _??_. Moreover two plants with 7_II+ 1_I have been found. They may have resulted from a non-disjunction of the two k-chromosomes in the 8-chromosome parent.
Thus crossing experiments have confirmed the assumption proposed in my previous paper (GOTOH 1924) that 8-chromosome plants arose from 7-chromosome ones through transversal segmentation into two of both members of the longest bivalent. Such fragmentation, and on the other hand rejunction of the two fragments, takes probably place in the first division after fertilisation.
LEVITSKY's (1930) 8-chromosome rye is discussed. The author assumes that in this case probably a secondary 8-chromosome rye was involved.