Pollen germination and tube growth in selfing and outcrossing populations of Clarkia tembloriensis (Onagraceae)

Pollen germination, pollen tube growth, and seed set were compared in growth chamber-grown plants derived from a typically outcrossing (Idria-2) and a typically selfing (Cantua Creek-2) population of Clarkia tembloriensis. Pollen of Idria-2 plants germinated uniformly and rapidly, usually within 1 h after pollination. Pollen of Cantua Creek-2 plants germinated more slowly, over a period of 1-7 h after pollination. The styles of Idria-2 plants were nearly twice as long as those of Cantua Creek-2 plants, but the time elapsed between the moment of pollination and when the pollen tubes reached the ovary was the same for both populations. However, even though the pollen tubes reached the ovaries at approximately the same time after pollination for all plants, fertilization of ovules, as measured by seed set, occurred immediately in the Cantua Creek-2 plants, while fertilization was delayed by 2-3 h in the Idria-2 plants. These differences in pollen germination and tube growth were significant and may have evolved in response to different levels of pollen competition in the two populations.