Self-pollination, style length development and seed set in self-compatible Asteraceae: evidence from Senecio vulgaris L.

Figures & data

Figure 1. Stages in style length development during phases of elongation and contraction in Senecio vulgaris. (A) Elongation phase scores: 1, style remains inserted in corolla tube just after floret has opened; 2, closed stigma protrudes from corolla apex; 3, style exserted just above rim of corolla tube with stigmatic lobes not completely unfurled; 4, style exserted from corolla tube with stigmatic lobes completely unfurled just above corolla rim; 5, style fully elongated with stigmatic lobes unfurled above corolla rim. (B) Contraction phase scores: 4, as 4 above; 3, similar to 3 above; 2, as 2 above, but stigmatic lobes remain partially unfurled with tips protruding from corolla tube apex; 1, as 1 above, but stigmatic lobes remain partially unfurled though fully reinserted into corolla tube.

Table 1. Frequency (%) of long and short styles with 0, 1, 2, 3 or >3 germinated pollen grains on their stigmas in the radiate and non-radiate variants of Senecio vulgaris in Scottish and Welsh populations.

			Number of germinated pollen grains per stigma
Variant	Style type	N	0	1	2	3	>3	(>0)
Radiate	Long	123	77.2	13.8	5.7	1.6	1.6	(22.8)
	Short	84	10.7	32.1	15.5	16.7	25.0	(89.3)
χ^2(1) = 88.33 (P < 0.001)
Non-radiate	Long	136	71.3	12.5	8.1	3.7	4.4	(28.7)
	Short	111	12.6	18.9	15.3	7.2	46.0	(87.4)
χ^2(1) = 85.12 (P < 0.001)

Frequencies were estimated after pooling data over populations. N equals number of styles sampled. χ² values are for 2×2 tests of independence of style length and frequency of stigmas with either 0 or >0 germinated pollen grains on them. P equals probability of independence.

Table 2. Frequency (%) of styles (pooled over populations) with 0, 1, 2, 3 or >3 germinated pollen grains on their stigmas of Senecio vulgaris in Scottish and Welsh populations.

			Number of germinated pollen grains per stigma
Variant	Style type	Floret position	N	0	1	2	3	>3	(>0)
Radiate	Long	Outer	58	86.2	5.2	6.9	0.0	1.7	(13.8)
		Inner	65	69.2	21.5	4.6	3.1	1.5	(30.8)
χ^2(1) = 5.017 (P = 0.025)
Non-radiate	Long	Outer	85	75.3	9.4	7.1	5.9	2.3	(24.7)
		Inner	51	63.5	19.2	9.6	0.0	7.7	(36.5)
χ^2(1) = 1.746 (P = 0.186)
Radiate	Short	Outer	27	7.4	22.2	14.8	25.9	29.6	(92.6)
		Inner	57	12.3	36.8	15.8	12.3	22.8	(87.7)
χ^2(1) = 0.4549 (P = 0.500)
Non-radiate	Short	Outer	53	13.2	24.5	11.3	7.6	43.4	(86.8)
		Inner	58	12.1	13.8	19.0	6.9	48.3	(87.9)
χ^2(1) = 0.0335 (P = 0.855)

Frequencies are presented for long- and short-styled florets located in the outer and inner whorls of capitula produced by the radiate and non-radiate variants. N equals number of styles sampled. χ² values are for 2×2 tests of independence of style length and frequency of stigmas with either 0 or >0 germinated pollen grains on them. P equals probability of independence.

Figure 2. Mean number of germinated pollen grains present on stigmas of styles in long- and short-styled florets of Senecio vulgaris in Scottish and Welsh populations. Standard errors are indicated as bars.

Figure 3. Mean style length scores of non-pollinated and self-pollinated florets of Senecio vulgaris at time of treatment (0 h) and at intervals of 6, 22, 24 and 48 h afterwards. Standard errors of means are indicated by bars.

Table 3. Mean seed set per floret of the radiate and non-radiate variants of Senecio vulgaris following placement of 1, 2–5 or 6–10 grains of self- or cross-pollen per stigma.

		Number of pollen grains per stigma
	Variant	1	2–5	6–10
Self-pollen
	Radiate	0.312 (SE = 0.094)	0.297 (SE = 0.161)	0.514 (SE = 0.066)
	Non-radiate	0.265 (SE = 0.134)	0.619 (SE = 0.098)	0.782 (SE = 0.128)
Cross-pollen
	Radiate	0.263 (SE = 0.047)	0.463 (SE = 0.138)	0.854 (SE = 0.042)
	Non-radiate	0.348 (SE = 0.094)	0.567 (SE = 0.098)	0.744 (SE = 0.063)

Standard errors (SE) are in parentheses.

Figure 4. Mean seed set per floret (across both radiate and non-radiate variants of Senecio vulgaris) following placement of 1, 2–5 or 6–10 grains of self- or cross-pollen per stigma. Standard errors are indicated as bars.