Crosses between sexual and apomictic dandelions (Taraxacum). I. The inheritance of apomixis

Abstract

Some dandelions, Taraxacum, are diplosporous gametophytic apomicts. Crosses between closely related diploid sexuals and triploid apomicts were made to study the inheritance of apomixis. Seed-set was less than one-third of that in diploid´diploid crosses, probably because of the inviability of aneuploid pollen or zygotes. Almost 90% of the viable ospring were diploid and the result of sel®ng, as was shown by a discriminating allozyme marker. Aneuploid outcross pollen had a mentor eect on self-pollen, causing a breakdown of the sporophytic self-incompatibility system. A similar phenomenon has been reported before in wide crosses. Of the 26 allozyme-con®rmed hybrids, four were diploids, 15 were triploids and seven were tetraploids. Diploid hybrids were signi®cantly less frequent than triploid hybrids, suggesting either low ®tness of haploid pollen or more numerous formation of diploid pollen. Emasculation and bagging of¯owers indicated apomictic seed-set in none of the diploid, in one-third of the triploid and in all of the tetraploid hybrids. All apomictic hybrids showed partial seed-set, but additional cross-pollination did not increase seed-set. Cytological analysis of the F 2 progeny con®rmed that partial apomixis was caused by semisterility and not by residual sexuality (facultative apomixis). The dierence in segregation for apomixis between triploid and tetraploid hybrids may be because the triploids originated from partially reduced diploid pollen grains, whereas the tetraploids originated from unreduced triploid pollen grains.

New chromosome counts and genome size estimates for 28 species of Taraxacum sect. Taraxacum

“…Although there is no evidence for the potential evolutionary scenario in European Taraxacum sections, we can speculate that the origin of apomictic species of T. sect. Taraxacum ( T.officinale group) may be a result of “recent” hybridization between triploid apomicts and diploid sexuals in the sexual-asexual cycle in a mixed dandelion population, a phenomenon experimentally described in this group (Tas and van Dijk 1999, van Dijk 2003, van Dijk and Vijverberg 2005). In a mixed population (2x and 3x cytotypes; sexual and apomictic types), triploids are results of hybridization between triploid apomicts (diploid pollen) and diploid sexuals (haploid egg cell); however, a rare occurrence of tetraploidy (probably of temporary occurrence) can accelerate the formation of novel triploids (Verduijn et al 2004b).…”

Geographic parthenogenesis and plant-enemy interactions in the common dandelion

“…Ploidy level was determined in leaf tissue from two seedlings from each collected capitulum, using a Partec Ploidy Analyzer ultraviolet flow cytometer to measure nuclear DNA content relative to a reference sample of known diploidy [70]. In virtually all cases the two seedlings were either both diploid or both triploid, indicating respectively sexual or apomictic status of the field-sampled mother plant [70]. In mixed populations with both diploids and triploids we screened an additional 30–70 plants to improve the estimation of the proportion of apomicts in the population.…”

Efficient long-term conservation of Taraxacum pieninicum synthetic seeds in slow growth conditions

“…Factors such as a small number of individuals and limited seeds germination due to the feeding of invertebrates, in particular snails, are a threat to the survival of this species. In addition, the seeds of Taraxacum species are difficult to store because germination of seeds occurs immediately after maturation and seeds lose their vitality significantly after 2 years of storage (Tas and Van Dijk 1999;Honek et al 2005).…”