Ruth Ingram

Chloroplast DNA and biosystematics: The effects of intraspecific diversity and plastid transmission

Summary Harris, S. A. & Ingram, R.: Chloroplast DNA and biosystematics: The effects of intraspecific diversity and plastid transmission. - Taxon 40: 393-412. 1991. - ISSN 0040-0262. The widespread application of chloroplast DNA (cpDNA) to plant biosystematics is usually based on a number of assumptions. The assumption of low levels of intraspecific cpDNA variation is reviewed and the conclusion reached that far from being rare, intraspecific cpDNA variation is relatively common. The evidence for the assumption of predominantly maternal plastid transmission is also reviewed. In both of the cases some of the possible effects on phylogenetic reconstruction are considered.

Molecular systematics of the genus Senecio L. I: Hybridization in a British polyploid complex

A survey of chloroplast DNA and nuclear ribosomal DNA variation was conducted in the allohexaploid Senecio cambrensis, the putative introgressant S. vulgaris var. hibernicus and their parental taxa: S. vulgaris var. vulgaris and S. squalidus. Ribosomal DNA allowed the differentiation of the two parental taxa and supported the hybrid origin of S. cambrensis at three of the four sites sampled; at the fourth site, in Edinburgh, non-additive rDNA phenotypes were found. No evidence, for or against the introgressive origin of var. hibernicus was found. Chloroplast DNA analysis provided independent evidence for the dual origin of S. cambrensis in Wales and Scotland, although the two parental taxa could not be distinguished.

A phylogenetic analysis of Leucaena (Leguminosae: Mimosoideae)

Chloroplast DNA restriction fragment length polymorphisms have been used to reconstruct the maternal phylogeny of all the known taxa in the small neotropical legume genusLeucaena. Three major plastome clades were recognized, but these did not conform with relationships between the taxa proposed on other characters from morphology, cytology or hybridization. The maternal parentage of tetraploids within the genus has been proposed. Evidence for introgression was found between “diploid”L. diversifolia and “tetraploid”L. diversifolia. The implications of these results for the origin of the cultivated taxa are discussed.

Synthesis of the hybrid Senecio squalidus L. × S. vulgaris L. F. radiatus hegi

SummaryHybrids between Senecio vulgaris L. f. radiatus Hegi and S. squalidus L. were obtained with little difficulty. This is in marked contrast to the experience of other workers attempting the cross using S. vulgaris L. f. vulgaris. The implication is that the spread of S. vulgaris f. radiatus may have important effects on the isolation of the species when it is in contact with S. squalidus.

The genomic relationship of Senecio squalidus L. and Senecio vulgaris L. and the significance of genomic balance in their hybrid S. × Baxteri druce

SummaryThe genomic relationship of S. squalidus L. and S. vulgaris L. is clarified by a cytological study of the offspring of the F1 hybrid between them. It is demonstrated that the effective gametes produced by the hybrid are all genomically balanced. The importance of this gametic selection in introgression is discussed.

Molecular systematics of the genus Senecio L. II: The origin of S. vulgaris L.

The origin of Senecio vulgaris L. and the relationship of its two subspecies, ssp. vulgaris and ssp. denticulatus (O. F. Muell.) P. D. Sell, are examined using nuclear ribosomal and chloroplast DNA analyses. No evidence was found to support either an allopolyploid or an autopolyploid origin of S. vulgaris, although it would appear that S. vernalis Waldst. & Kit. is not one of the progenitor taxa. Two results of particular interest were found: (i) the apparent identity of the chloroplast genomes of S. vulgaris ssp. vulgaris and S. squalidus L. and (ii) the divergence of the chloroplast genomes of ssp. vulgaris and Ainsdale ssp. denticulatus by at least eight site mutations. These results are discussed in the light of evidence derived from morphological, cytological and allozyme studies.

The control of chiasma formation in colchicine treated meiocytes of Senecio squalidus

Colchicine induced multivalent formation is used to examine the effects of multivalent formation on chiasma frequency in Senecio squalidus. The increases observed are interpreted as the results of increases in numbers of pairing segments or decreases of chiasma interference following pairing partner exchange.