Selectively advantageous effects of B chromosomes on germination behaviour in Allium schoenoprasum L.

Abstract

The effects of B chromosomes in Allium schoenoprasum on germination rate and on the ability of seeds to germinate under drought conditions have been investigated. When water was freely available for germination, there was an increased frequency of B-containing individuals amongst the first 10 per cent of seeds to germinate compared with the middle germinating group (64 cf. 56 per cent). Two drought regimes were employed: in one ('droplet') seeds were provided with a limited amount of water, and in the other ('PEG') the availability of water was limited osmotically. There was a significantly increased frequency of B-containing individuals amongst the 5 per cent of seeds that were able to germinate in both the droplet sample (79 per cent) and the PEG sample (65 per cent) compared with the control sample (56 per cent). Although the early and drought germinating groups had higher frequencies of B-containing seedlings, the individual seedlings did not carry a significantly increased number of B chromosomes. The increases in the frequencies of B-containing seedlings in the early and drought germinating groups were comparable to or greater than that observed previously in the wild between the seed and seedling stages, suggesting that the increased survival of B-containing individuals in natural populations could be due to the effects of Bs on germination behaviour. There was no relationship between the presence of B chromosomes and seed size, seed density or seed shape, implying that differences in these seed characteristics do not provide an explanation of the effects of B chromosomes on germination.

Bewildering Bs: an impression of the 1st B-Chromosome Conference

“…Peculiarly, being raised at a selfish DNA school, I was struck by the clear evidence for the beneficial effects of some Bs (e.g. the case of A. schoenoprasum, Plowman & Bougourd, 1994). We may now have reached a stage where both models are considered valid.…”

“…Other control factors could be maternal effects (e.g. Puertas et a!., 1990), cytotype (Beukeboom & Werren, 1992) (Plowman & Bougourd, 1994). In E. plorans (Lopez-Leon et al, 1992) there is no drive (transmission rate is 0.5) and no selective elimination through harmful effects.…”

The B-chromosome polymorphism of the grasshopper Eyprepocnemis plorans in North Africa: II. Parasitic and neutralized B1 chromosomes

“…Some B chromosomes are good candidates to be heterotic since they have an obvious beneficial effect on carrier fitness (eg, Nectria haematococca (Miao et al, 1991a, b) and Avena sativa (Dherawattana and Sadanaga, 1973)), but their population dynamics has been analysed only in Allium schoeno- Correspondence: Dr M Bakkali, Departamento de Genética, Facultad de Ciencias, Universidad de Granada, 18071, Granada, Spain. E-mail: mbakkaliȰugr prasum, where Bs lack drive and are beneficial in increasing viability from seed to seedling (Holmes and Bougourd, 1989;Plowman and Bougourd, 1994). Camacho et al (1997) have proposed a long-term model for the evolution of parasitic B chromosomes, in which the establishment of a B chromosome depends on the existence of an accumulation mechanism facilitating the initial increase in B frequency, surpassing possible deleterious effects on host fitness.…”

Cytotaxonomy of Allium (Amaryllidaceae) subgenera Cyathophora and Amerallium sect. Bromatorrhiza

“…drought and cold climate, high elevation, etc.) (Plowman & Bougourd 1994, Chen et al 2005, Wu et al 2010. However, a possible correlation among Bs and polyploids concerning their role to species adaption needs more researches.…”