No abstract

In genetically-heterogeneous outcrossing species, there is the opportunity for selection based on the male gamete . Buckwheat (Fagopyrum esculentum Moench) is self-incompatible with one ovule per flower, so pollen competition at each ovule can be studied . The occurrence of selection among pollen parents was determined, as well as the relative importance of prezygotic and post-zygotic selection . Mixed pollinations from two donors produced nonrandom paternity, with one of the donors being favored about 2 :1 on several females . Individual plants showed significant variation in the speed of pollen-tube growth . Therefore, prezygotic selection is likely to have occurred based on the speed of pollen tube growth . In single-donor pollinations, donors had equal success as expected in the absence of post-zygotic selection among donors . However, a significant male x female interaction was found, consistent with postzygotic selection against particular parental combinations . To test whether male fitness is reduced by increased allocation to seed filling during pollen production, large-and small-seeded lines were compared, both as pollen donor and as pollen recipient . The large-seeded line was better in both roles, thus there was no evidence that greater allocation to seeds reduced the quality of the pollen .

Production of broccoli in areas where summer temperatures exceed 30C is difficult because the head may not form properly. The high temperature causes an unevenness in the head due to widely differing sizes of buds. The sensitive stage of development was determined for the early maturing variety `Galaxy' by exposing it to 1-week at 36C at varying developmental stages, and subsequently analyzing the head structure. The injury is a cessation of bud enlargement during the high-temperature exposure. There is no corresponding cessation of bud initiation at the apex. The patter of injury is consistent with susceptibility over a relatively small range of bud development: even with a 1-week exposure, only about 1/3 of the buds will be affected. The plant's most developmental stage at this sensitive period still appears vegetative, but the youngest leaves are just beginning to reorient as a consequence of the reduced stem elongation rate. The meristem is less than 1 mm wide, and scanning electron micrographs show floral primordia just forming, still subtended by leaf primordia. The injury is fully expressed when the head is first exposed (≈10 mm wide), though it becomes more apparent as the head matures. The buds that were delayed in development by the high temperature developed into fertile flowers, albeit about a week late.