Self-incompatibility in Cosmos atrosanguineus: a rare Mexican endemic species of Asteraceae

Lewendon, Sarah (2005) Self-incompatibility in Cosmos atrosanguineus: a rare Mexican endemic species of Asteraceae. PhD thesis, University of Greenwich.

Abstract

Cosmos atrosanguineus, exhibits strong sporophytic self-incompatibility (SSI), does not set seed, and must be propagated vegetatively, a factor that has contributed to the proliferation of closely related or identical genotypes. Microsporogenesis within the species appears normal, with no discernible differences between microsporogenesis in C. atrosanguineus and two seed-producing Cosmos species. The C. atrosanguineus karyotype and chromosome associations at meiosis identify the species as an allotetraploid that produces viable gametes with ~30% pollen viability. Self- and cross-pollinations of C. atrosanguineus are strongly incompatible with an average of zero pollen grains germinating per stigma. In contrast, cross and self-pollinations in C. bipinnatus and C. sulphurous produced three compatibility groups; incompatible (-), compatible (+) and semi-compatible (±) and four categories of pollen-stigma interaction that putatively identify a gametophytic-sporophytic (G-S) incompatibility system in Cosmos. Dominance interactions of S-alleles are prevalent in the genus and pseudo-self-compatibility was observed in C. bipinnatus but not C. atrosanguineus. The Cosmos stigma is dry, papillate and becomes receptive only after stigmas become reflexed. Prior to this period, the stigmas do not respond to pollination and selfed bud pollinations and crossed bud pollinations are incompatible. Degenerate S-specific primers identified 41 S-domain-encoding sequences from Cosmos and four other genera of Asteraceae. These 41 Asteraceae sequences encoded S-domains related to Brassica S-domain proteins, but none identified as a putative self-incompatible molecule, indicating the control of SI in Cosmos is probably different to that in Brassica. Genetic fingerprinting (AFLP) of various European sources of C. atrosanguineus showed no genetic variation. In conclusion, Cosmos atrosanguineus is a strongly self-compatible species with a reduced genome.

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