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. © The Genetical Society of Great Britain.