Frequencies of genetical factors determining male sterility in onion (Allium cepa L.) and their significance for the breeding of hybrids

Summary In selections of some more or less commonly grown onion varieties in the Netherlands the frequencies of genetical factors governing male sterility were determined. In the leading Dutch variety Rijnsburger the chromosomal factor ms was found to occur in a frequency of over 0.95 and the cytoplasmic factor S in a frequency of less than 0.01.As a consequence, a programme of breeding hybrid onions with the aid of this variety can be started in a simple way by selfing selected plants to produce B lines. Simultaneously seed is harvested from male-sterile plants in the same variety. Subsequently in the third, fifth or seventh year, backcrossing can be started to obtain corresponding A lines. For backcrossing the progenies of the initially selected male-sterile plants are used.The choice of the year in which backcrossing will be started depends mainly on circumstances and on one's personal views.