INFLUENCE OF TEMPERATURE AND AGING OF OVULES AND POLLEN ON REPRODUCTIVE SUCCESS IN TRIFOLIUM-REPENS L

Four clones of Trifolium repens L., originating from Iceland, Denmark and Israel, were cultivated in controlled environment chambers at 10, 14, 18 and 22 degrees C. Seed set at 10 degrees C was, on average, 45% lower than at 18 degrees C. Generally, seed frequencies were higher in the stylar ovule positions than in the basal. This polarization became more pronounced at low temperatures. At least 30% of the decrease in seed set was caused by inadequate pollen tube growth. This was further supported by in vitro studies which showed that pollen developed significantly shorter pollen tubes at low temperatures and a strong positive correlation between the capacity of male parents to induce seed set in basal ovule positions and the length of pollen tubes in vitro. Female age, determined by days relative to anthesis, was also found to have a significant influence on seed set, i.e. when pollination was delayed until the fifth day of flowering, seed set decreased by an average of 60% when compared to florets pollinated on the first day of anthesis. Pollen age did not influence seed set. Ageing of pollen decreased in vitro germinability, tube elongation and the percentage of pollen tubes with sperm cells. Seed set, pollen germinability, pollen tube lengths, and ability to form sperm cells in vitro varied significantly among clones.