Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 244

Allogamous species depend on agents of pollination, especially wind and insects, and hence tend to produce large amounts of pollen, and have large, bright‐colored fragrant flowers to attract insects. They commonly have taller stamens than carpels or use other mechanisms to better ensure the dispersal of pollen to other plant flowers. Other provisions that promote cross‐fertilization are mechanisms that control the timing of the receptiveness of the stigma and shedding of pollen and thereby prevent autogamy within the same flower. In protandry, the anthers release their pollen before the stigma of the same flower is receptive (protandrous flower). In protogyny, the stigma is receptive before the pollen is shed from the anthers of the same flower (protogynous flower). Several mechanisms occur in nature by which cross‐pollination is ensured, the most effective being dioecy, monoecy, dichogamy, and self‐incompatibility. Some mechanisms are stringent in enforcing cross‐pollination (e.g. dioecy), while others are less so (e.g. monoecy). These mechanisms are exploited by plant breeders during controlled pollination phase of their breeding programs, so that only desired pollen sources participate in siring the next plant generation.