SELECTIVELY ADVANTAGEOUS EFFECTS OF B-CHROMOSOMES ON GERMINATION BEHAVIOR IN ALLIUM-SCHOENOPRASUM L

The effects of B chromosomes in Allium schoenaprasum on germination ra te and on the ability of seeds to germinate under drought conditions h ave 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 emplo yed: in one ('droplet') seeds were provided with a limited amount of w ater, and in the other ('PEG') the availability of water was limited o smotically. There was a significantly increased frequency of B-contain ing individuals amongst the 5 per cent of seeds that were able to germ inate 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-cont aining seedlings, the individual seedlings did not carry a significant ly 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 wi ld 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 relati onship between the presence of B chromosomes and seed size, seed densi ty or seed shape, implying that differences in these seed characterist ics do not provide an explanation of the effects of B chromosomes on g ermination.