Variability of outcrossing frequency in Senecio vulgaris L.

Abstract

SUMMARYUsing a marker gene controlling capitulum type, 30 lines derived from each of a dune and a garden population of Senecio vulgaris L. were tested for their tendency to outcross. Compared with previous estimates of outbreeding in the species a relatively high degree of outcrossing was found in both experimental populations (an overall average of 224 per cent). It was shown that the dune population had a slightly greater mean outcrossing frequency than the garden population but, more importantly, had significantly more heritable variation (between lines) for this trait. In discussion, some reasons are advanced to account for the unexpectedly high level of outcrossing in both populations. It is suggested that the presence of significant genetic variation for outcrossing within the dune population may provide for adaptive flexibility in the native dune habitat where there is much spatial and temporal variation of the environment.

Inhibition of self pollen germination in Senecio vulgaris L.

“…Because each plant was selfed, and also provided pollen for one cross chosen at random, the differences found between selfs and crosses at 24 hours (table 2) will not reflect defective pollen from any one plant. When cross pollinated (table 3), a vast range of crossing frequencies was observed in all treatments, showing a high potential for outbreeding; similar ranges were reported from open-pollinated plots by Campbell and Abbott (1976). Since self pollen was already present upon stigmas before crossing occurred, it is remarkable to find that some capitula set 100 per cent crossed seeds.…”

“…The ray-floret locus itself has been used as a marker to measure inter-morph outcrossing rates in S. vulgaris (Campbell and Abbott, 1976;Abbott, 1982, 1984a). Without the existence of another, unlinked marker locus it is impossible to estimate intra-morph outcrossing rates.…”

“…The species used to be considered highly inbred, with reproduction verging on complete autogamy (Gibbs et a!., 1975), but in experimental plots Campbell and Abbott (1976) found an average outcrossing rate of 224 per cent in nonradiate lines. Furthermore, Abbott (1982, 1984a), using the ray floret locus as a marker, showed that in populations polymorphic for capitulum type, the radiate morph had a greater "female" outcrossing frequency than the nonradiate morph.…”

Outcrossing frequencies within- and between-capitulum morphs in groundsel Senecio vulgaris L.

“…The levels of inter-morph outcrossing observed both here (tables 1 and 2) and also by Campbell and Abbott (1976) might be expected to result in a large number of short-rayed heterozygous plants in the wild. Hull (1974) and Oxford and Andrews (1977), however, have reported that such heterozygous plants are conspicuous by their rarity in natural populations.…”

“…Gibbs et al (1975) also considered it to be a highly inbred species, to the point of autogamy. In experimental plots, however, levels as high as 22 per cent female outcrossing have been recorded in non-radiate lines (Campbell and Abbott, 1976).…”