Cytoplasm of a Wild Species, Allium galanthum Kar. et Kir., is Useful for Developing the Male Sterile Line of A. fistulosum L.

Abstract

To develop the male sterile line of Allium fistulosum L., cytoplasmic substitution by continuous backcrossing was performed using A. galanthum Kar. et Kir. as a cytoplasm donor. Pollen and seed fertility in F1 hybrid and the backcross progenies were examined. In backcrossing, progenies were selected in the direction of high seed fertility from B1 generation and in the directions of low and high pollen fertility from B2 generation. The pollen fertility in F1 hybrid was 65% ; that in B1 and B2 generations varied from 10 to 77%, 0 to 98%, respectively. Almost all plants in B3, B4, and B5 generations selected in the direction of low pollen fertility were pollen sterile. The decrease of pollen fertility in F1 hybrid is attributed to the hybridity of nuclei. However, it is difficult to relate pollen sterility observed in the backcross progenies to the hybridity of nuclei because the nuclei of those plants are mostly composed of genomes of A. fistulosum. Therefore, it is concluded that the pollen sterility observed in the backcross progenies is attributed to incompatibility between the cytoplasm from A. galanthum and the nucleus from A. fistulosum. In each of B3, B4, and B5 generations selected in the direction of high pollen fertility, pollen fertile and pollen sterile plants segregated at a ratio of approximately 1 to 1. This finding strongly indicates that the pollen fertile plants had a single dominant fertility restoring gene which originated from the nuclear genome of A. galanthum and that the pollen sterile plants had not this gene. Although the seed fertility somewhat varied among the progenies at each backcross generation, it could be improved with frequency of backcrossing, and some plants had higher seed fertility than A. fistulosum. Analyses of chloroplast and mitochondrial DNAs proved that all the backcross progenies examined inherited the cytoplasm from A. galanthum. From these results, we conclude that the cytoplasm of A. galanthum is useful for developing the male sterile line of A. fistulosum.