Selection at the Ms locus in open pollinated onion (Allium cepa L.) populations possessing S-cytoplasm or mixtures of N- and S-cytoplasms

Abstract

The bulb onion (Allium cepa L.) was historically seed propagated by open pollination (OP). Cytoplasmicgenic male sterility (CMS) and protandry encourage outcrossing among individual onion plants. The most common source of CMS in onion is conditioned by the interaction of sterile (S) cytoplasm with a single nuclear male-fertility restoration (Ms) locus. We previously reported that the majority of OP onion populations possess normal (N) male-fertile cytoplasm and varying frequencies of the dominant Ms allele. It was unclear why N-cytoplasmic onion populations often possess relatively high frequencies of the Ms allele, which has no obvious function. We used computer simulations to estimate changes in allelic frequencies at Ms for onion populations possessing S-cytoplasm or a mixture of N-and S-cytoplasms, and to determine if frequencies of the Ms allele stay constant or change due to failure of male gamete production from malesterile (S msms) plants. The models revealed selection against the recessive ms allele over generations in onion populations possessing S-cytoplasm and varying amounts of self pollination and inbreeding depression. These models were consistent with field and molecular analyses documenting that N-cytoplasm and the dominant Ms allele predominate in OP onion populations.

Limitations of PCR‐based molecular markers to identify male‐sterile and maintainer plants from Indian onion (Allium cepa L.) populations

“…In India, Pathak () crossed a male‐sterile line with several fertile lines which included both indigenous and exotic accessions and found that all hybrids were male sterile which lead to two distinct possibilities (i) either all the germplasm lines involved in the crossing programme had recessive ms genes, or (ii) the male‐sterile cytoplasm was not restored by the nuclear genes. The possibility of all the lines having ms genes is very unlikely 0 based on the simulation studies carried by Gökçe and Havey () where simulation produced 60% recessive allele frequency after 25 generations given that the starting frequency was 79% as reported by Little et al. ().…”

Perspectives of onion hybrid breeding in India: An overview

“…Male sterile cytoplasms in onion N-cytoplasm: Normal (N) cytoplasm might have been developed from Allium vavilovii and is reported to be the progenitor of onion cytoplasm and this cytoplasm is predominant in occurrence in wild and domesticated Allium species of Central Asia (Havey 1997). In open pollinated onion populations, this type of cytoplasm is dominant with high frequency of dominant fertility restorer (Ms) alleles Randle 1996, Gökçe andHavey 2006). The major reason is continuous selection of dominant against recessive alleles over several y e a r s a n d generations.…”