THE POPULATION CYTOLOGY OF SCILLA AUTUMNALIS
MetadataShow full item record
Scilla autumnalis L. (the autumn squill) is a bulbous member of the Liliaceae. S. autumnalis has a circum-Mediterranean distribution and is restricted to open, free draining sites. In England S. autumnalis is a plant of open habitats in which the vegetation remains very short. Reproduction is exclusively by seed. Cytological investigation of population samples from England, the Channel Islands, northern France, Greece and Portugal have revealed that S. autumnalis is a polyploid complex. The complex comprises six cytologically distinct races, involving two separate genomes A and B; a diploid BB (2n = 2x = 14), a diploid AA (2n = 2x = 14), an allotetraploid AABB (2n = 4x = 28), an autotetraploid BBBB (2n = 4x = 28) , an autoallohexaploid AABBBB (2n = 6x = 42) and an autohexaploid BBBBBB (2n = 6x = 42). There is no homology between the two genomes and the A genome is 43% longer than the B genome. No populations have been found which contain a mixture of chromosome races. Plants of the six chromosome races are morphologically very similar even though there has been considerable differentiation of the two genomes. A possible scheme for the evolution of the polyploid complex is proposed. The chromosomal structure of populations of BB diploid. BBBB auto tetraploid and AABBBB autoallohexaploid races has been investigated ~n forty-five populations from England. the Channel Islands and Corfu (Greece). The incidence of chromosomal variation, both structural and numerical is extraordinarily high in all three races. Numerical variation comprised aneusomaty. aneuploidy, polysomaty and polyploidy. The extent of numerical variation increased with ploidy level. Hexaploids were unstable 1n somatic tissues. Structural variation 1n S. autumnalis is of three types; spontaneous between-cell, whole plant unique and whole plant polymorphic. The frequency of all three increases with ploidy level. Of the structural changes affecting whole plants, deletions, inversions and duplications were common but only the latter two were involved in polymorphic systems. Forty-five polymorphisms were detected, some of which were geographically widespread. Three polymorphisms were present in more than one chromosome race. The number of polymorphisms in a population is negatively correlated with latitude. Peripheral populations show less variation than central populations.
AuthorsAinsworth, Charles C.
- Theses