Self-fertility studies in three species of commercial grasses

1. Clonal lines of creeping brome grass, crested wheatgrass, and meadow foxtail were grown in replicated trials and seed setting was studied under conditions of open-pollination and under isolation by the use of bags. Brome and crested wheat were studied both in 1943 and 1944 and meadow foxtail only in 1944. Significant differences in seed setting between clonal lines within each of the three species were obtained both under open-pollination and under bags. There were wide differences also due to seasonal conditions. 2. Under open-pollination conditions, 3 of the 29 S2 or open-pollinated plants of brome grass, 6 of the 12 S2, S1, or open-pollinated plants of the forage type crested wheat grass, and 1 of the 24 S1 or open-pollinated plants of meadow foxtail were definitely low seed-producers. Clones of the forage type of crested wheat average lower in seed production than did those of the Fairway type. In brome grass a number of S2 lines were distinctly lower in seed production than open-pollinated plants, but this was not true for S1 lines of crested wheat and meadow foxtail. 3. Under isolation in parchment bags, 19 of 29 clones studied in creeping brome, 3 of 34 clones in crested wheatgrass, and 23 of 24 clones in meadow foxtail were found to produce sufficient seed for the production of selfed plant progenies. Others were highly self-sterile. Self-fertility in crested wheatgrass was very low when compared with that in brome grass and meadow foxtail. Self-fertility in meadow foxtail was definitely higher than in brome grass and much higher than in crested wheatgrass. 4. In both brome grass and crested wheatgrass, seed setting under space isolation was higher than that under isolation in parchment bags. The few clones isolated in pairs indicate also that increased fertility could be obtained in this manner. 5. Positive and significant inter-annual correlations were found in seed setting under open pollination in 1943 and 1944 for brome grass and crested wheatgrass, which indicated hereditary differences in seed-setting ability. Other correlations were reported between seed setting under various conditions. The only positive relationship of great importance was the significant r value between seed setting under bags and under space isolation in brome grass. 6. There was no consistent relationship between the diameter of pollen grains and seed-setting ability in the clones of the three species. This was true also in comparisons between forage and Fairway types in crested wheatgrass, indicating no relation between chromosome number and pollen size, the forage type having 2n = 28 and Fairway 2n = 14 chromosomes. 7. For the clones of brome grass and crested wheatgrass, there was a significant negative correlation between the percentage of aborted pollen and the number of viable seeds produced per sample under open-pollination conditions. The correlation between pollen abortion and seed setting under bags in meadow foxtail was not significant. 8. In brome grass, a close relationship was found between the percentage of aborted pollen of a clone and the frequency of quartets showing micronuclei. In meadow foxtail, no such definite relation was evident.