Sj. Hiscock, Genetic control of self-incompatibility in Senecio squalidus L. (Asteraceae): a successful colonizing species, HEREDITY, 85(1), 2000, pp. 10-19
Senecio squalidus (Oxford ragwort) is a well-known introduction to the Brit
ish flora that has proved to be an extremely successful colonist over the l
ast 150 years. Unusually for a colonizing species, S. squalidus is self-inc
ompatible (SI). Being a member of the Asteraceae, SL in S. squalidus is exp
ected to be sporophytic. This paper presents genetic data showing that the
SI system of S. squalidus is indeed sporophytic and is controlled by a sing
le multiallelic S locus, alleles of which show the dominance/recessive rela
tionships characteristic of sporophytic SI (SSI). Early indications are tha
t the number of S alleles in populations is low because only four different
S alleles were identified in a sample of four plants from two distinct pop
ulations; one S allele, S-1, a pollen/stigma recessive allele, was present
in all four plants. Forced inbreeding, using salt-treatment to overcome SI,
was shown to generate 'pseudo-self-compatible' individuals with weakened S
I and a loss/reduction in stigmatic S-specific discrimination. Relatively h
igh frequencies of unpredictable compatible crossing 'anomalies' suggest th
at a 'gametophytic element' may influence the outcome of crosses in certain
genetic backgrounds so as to increase levels of compatibility when S allel
es are shared. Together, these findings indicate a genetic 'flexibility' in
the SSI system of S. squalidus that could be crucial to its success as a c
olonizer.