Thecyanogenicpolymorphismintrifoliumrepensl.(whiteclover)

Abstract

The genetic basis of male sterility in the gynodioecious species Plantago coronopus was studied. As the aim was to find strains with a single, varying nuclear locus for male sterility, cytoplasmic variation was avoided by starting with one open pollinated female. The progeny appeared to vary for a single locus with the homozygous recessive being male sterile. The locus was designated msl. Expected segregation ratios were disturbed by two different factors, both leading to a shortage of male steriles. An accidental drought in Petri dishes caused a relatively higher mortality of seedlings with a male sterility genotype in most cases. When this effect was avoided a systematic shortage of male steriles remained in many crosses. An experiment with varying levels of pollen competition justified the interpretation that selection at the gametophytic stage was involved. Pollen carrying the sterility allele was estimated to have a fertilization success relative to pollen with the restorer allele of 0.56. Finally the role of the msl locus in the genetics of male sterility in natural populations was assessed by crossing heterozygously and homozygously restored plants with male steriles collected from the wild. It appeared that the inheritance of male sterility is more complicated than the msl locus alone, which was expected. If the selection effects on the msl locus observed in this study occur in nature, this would have interesting consequences for the evolutionary dynamics of gynodioecy. © 1991 The Genetical Society of Great Britain.