Ramsey M
Department of Botany, University of New England, 2351, Armidale, New South Wales, Australia.
Department of Zoology, University of New England, 2351, Armidale, New South Wales, Australia.
Oecologia. 1995 Jul;103(1):101-108. doi: 10.1007/BF00328430.
The extent, frequency and causes of pollenlimited seed production were examined in partially selffertile populations of Blandfordia grandiflora for 2 years. Percentage seed set of open-pollinated plants (50-57%) did not differ within or between years, and was about 19% less than experimentally cross-pollinated plants (70-75%). Floral visits by honeybees did not differ through the flowering season and the number of pollen grains deposited on stigmas within 12 h of flowers opening exceeded the number of ovules per flower, indicating that the quality rather than the quantity of pollination limited seed set. Pollen limitation was caused by concurrent self- and cross-pollination and the subsequent abortion of some selfed ovules due to inbreeding depression. Natural seed set (55%) was intermediate between selfed (43%) and crossed (75%) flowers and was not increased when flowers that had been available to pollinators for 24 h were hand cross-pollinated, suggesting that ovules were already fertilized. Similarly, experimental pollination with both cross and self pollen within 24 h of flowers opening did not increase seed set relative to natural seed set, indicating that both cross- and self-fertilizations had occurred. In contrast, when selfing followed crossing by 48 h, or vice versa, seed set did not differ from crossed-only or selfed-only flowers, respectively, indicating that ovules were pre-empted by the first pollination. Collectively, these results indicate that under natural conditions self pollen pre-empts ovules, rendering them unavailable for cross-fertilization. This selfing reduces fecundity by 50%, as estimated from the natural production of cross seeds when selfing was prevented. Consequently, selection should favour floral traits, such as increased stigma-anther separation or protandry, that reduce interference between male and female functions that leads to selfing.
在两年时间里，对大花布氏草部分自交可育种群中花粉限制种子产量的程度、频率和原因进行了研究。开放授粉植株的结实率（50%-57%）在不同年份间或年份内并无差异，且比人工异花授粉植株（70%-75%）低约19%。蜜蜂的访花次数在整个花期并无差异，且花朵开放12小时内落在柱头上的花粉粒数量超过每朵花的胚珠数量，这表明授粉的质量而非数量限制了结实率。花粉限制是由自花授粉和异花授粉同时发生，以及随后部分自交胚珠因近亲繁殖衰退而败育所致。自然结实率（55%）介于自花授粉（43%）和异花授粉（75%）的花朵之间，当已对传粉者开放24小时的花朵进行人工异花授粉时，结实率并未增加，这表明胚珠已经受精。同样，在花朵开放24小时内用异花和自花花粉进行实验授粉，相对于自然结实率，种子产量并未增加，这表明异花受精和自花受精都已发生。相比之下，当自花授粉在异花授粉48小时后进行，或者反之，结实率分别与仅异花授粉或仅自花授粉的花朵并无差异，这表明胚珠被首次授粉抢先占据。总体而言，这些结果表明，在自然条件下，自花花粉抢先占据胚珠，使其无法进行异花受精。这种自花授粉使繁殖力降低了50%，这是根据防止自花授粉时异花种子的自然产量估算得出的。因此，选择应有利于花部性状，如增加柱头与花药的间距或雄蕊先熟，以减少导致自花授粉的雌雄功能之间的干扰。
