Inheritance of Cytoplasmic Male Sterility in Allium fistulosum L. (Welsh onion)

Abstract

The mode of inheritance of male sterility, discovered in Allium fistulosum by Nishimura et al. (1972), was investigated by three successive backcrossings and crosses between the second backcrossed plants and 7 varieties. The segregation ratio of sterility and fertility in the pollens and seeds was tested to determine the genes involved in male sterility.
The materials used were male sterile plants MS, hybrids F₁, families backcrossed to ‘Kaga’ (B₁ B₂ and B₃) and 7 other varieties (‘Kaga’, ‘Choju’, ‘Koshizu’, ‘Towada’, ‘Kujo’, ‘Kincho’ and ‘Ishikura esu’). The male sterile plants were usually used as the female. The male sterile plants obtained by the backcross were used in the cross with the pollinator (recurrent parent ‘Kaga’) or the 7 other varieties. Polle and seed fertility was determined by shape and color when stained with acetocarmine, and by the presence of mature seeds.
All plants obtained by the three successive backcrossings had sterile pollen and seeds, indicating that the male sterility of plant MS is controlled by cytoplasmic factors. In these experiments, segregation ratios of 1:3, 0:1, 1:1 and 1:0 for the sterility and the fertility of the pollens and seeds were observed in the progenies of the cross between the male sterile plants (B₂) and 7 varieties and in the selfed progenies.
From these results, it is apparent that male sterility is controlled by the interaction between the cytoplasm and nuclear genes and that the recurrent parent ‘Kaga’ is a maintainer. From the segregation ratios obtained in these experiments, the genotypes of the male sterile plants and the maintainer are assumed to be Sms₁ ms₁ms₂ms₂ and Nms₁ms₁ms₂ms₂. Male sterility may be used for the breeding of hydrid varieties of Allium fistulosum.