Cross- and Self-Incompatibility in Relation to Seed-Setting in Bromus inermis

Abstract

1. Interplant compatibility among fourteen plants of inbred origin and fifteen plants from open-pollination in smooth bromegrass (Bromus inermis Leyss.) was studied by determining the percentage seed-set following self-pollination and that accompanying mutual-pollination in clonally replicated diallel crosses. 2. The two groups of plants of inbred and open-pollination origin, respectively, were found to differ significantly within groups in self-compatibility. The frequency distribution of seed-set by plants of inbred origin following self-pollination was strongly skewed in the direction of incompatibility. 3. The plants studied differed significantly in number of seeds set when used as parents in mutual-pollination crosses in all combinations. 4. Highly significant differences between reciprocal crosses in number of seeds set were observed for plants of both inbred and open-pollination descent. 5. Genetic differences among plants for cross-compatibility reactions were indicated by the differential numbers of seeds set by the clones of any one plant when crossed each with a separate pollen parent. 6. Good agreement between years was observed for both groups of plants for seed-set following self- and open-pollination. Plants which proved compatible in crosses the first season were generally compatible in those same crosses the second season, and similarly for the incompatible matings, though specific agreement often was poor. 7. Both additive and nonadditive gene action are thought to influence seedset in diallel crosses. It is concluded that the general level of fertility of each plant is effected by genes acting additively, whereas nonadditive gene action appears to be causally related to specific cross-incompatibility effects. 8. The percentage of seed set by a plant in its most compatible mutual-pollination mating was positively and significantly correlated with the percentage of seed set by that plant following open-pollination. The effect was more pronounced among plants which had been inbred for two or more generations. It is concluded that under conditions of open-pollination fertilization of each plant is effected by the most compatible pollen present. The assumption of random pollination under these conditions appears to be unwarranted on the basis of data presented.