The genetics of self-incompatibility in Brassica campestris L. ssp. Oleifera Metzg. II. Genotypic and environmental modification of S locus control

Continuous variation in the expression of self-incompatibility, from complete self-incompatibility to self-compatibility, was observed among plants of the spring turnip rape cultivar Arlo. Significance of the variation between inbred progenies of plants from the base population suggested that a polygenic system had some influence on the expression of self-compatibility. The responses to one generation of selection within some of these progenies supported this conclusion. Further evidence of the operation of some polygenic modifying complex was provided by an analysis of a diallel cross among seven of the inbred lines. The analysis detected significant additive genetic variation among the parental lines, considerable non-allelic interaction and some dominance of an ambi-directional type.Significant seasonal variation in the expression of self-compatibility was observed in Arlo, the level of self-compatibility being substantially higher in summer than in winter. Under controlled environments, an increase in temperature from 25°C to 30°C resulted in a significant increase in the level of self-compatibility. The extent to which self-compatibility was affected by temperature differed among lines which were homozygous for a specific S allele.