Test of the first-in, first-in pollination hypothesis in coastal Douglas-fir

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Abstract
The hypothesis that pollen arriving first to receptive seed-cone buds has an advantage over pollen arriving later (first-on, first-in) was tested in Douglas-fir using two reciprocal pollination experiments. In the first test, one each of two outcross-pollen parents was applied first followed by the other 5 min or 24 h later. In the second test, self- and outcross-pollen parents were compared in a similar reciprocal arrangement 5 min, 6 h, and 24 h apart. Electrophoretic analysis of isocitrate dehydrogenase alleles was used to distinguish between the two pollen parents in resultant seeds. When a second pollen parent arrived within 5 min of the first, both contributed to the seed produced. However, when the second pollen parent arrived 6 or 24 h later, its contribution to the resultant seed was less. Pollen fertility potential interacted with arrival time and affected both seed yields and parental composition. When pollen of lower fertility was applied first followed by a higher fertility pollen, seed yields were lower; as the time interval for the arrival of the second pollen parent increased to 24 h, the percent contribution of the first pollen increased. However, when the higher fertility pollen was applied first, there was little effect of the lower fertility pollen arriving within 5 min or 24 h.

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