| The plants of the monosomic addition line and the disomic addition line
both showed very characteristic appearances. They had rather shorter culms
and selenderer spikes. This aberration was evidently caused solely by the
added cylindrica chromosome (s). Table 1 shows the effects of the added cylindrica chromosome (or chromosomes) on the fertility of Jones Fife. The monosomic addition line set a few plump seeds and many aborted ones on a spike by either artificial pollination or self-pollination. The aborted seeds were flattened and seemed to have no embryo and endosperm ; they did not germinate at all. Therefore, the seed-set ratios of viable seeds (plump ones) were only 14.9% (23 seeds set out of 154 florets) by crossing and 12.3% (37 out of 300) by selfing. The pollen fertility of the monosomic addition line on the other hand was almost normal in appearance. In contrast the disomrc addition plants had a nearly normal fertility of both sexes. They set seeds in 76.9% of florets by crossing (20 out of 26) and 81.7% of florets by selfing (98 out of 120). They did not produced aborted seeds. In short, the monosomic addition of the cylindrica chromosome to Jones Fife reduced the seed fertility strikingly, while disomic addition of that chromosome exerted no effect on the fertility of Jones Fife. In respect to transmission of the cylindrica chromosome, chromosome constitutions of the viable offspring of the monosomic addition line were examined. and the results are given in Table 2. All the offspring except three (16 plants) had 2n=43 chromosomes which included the cylindrica chromosome when the monosomic addition line was crossed as female with normal Jones Fife. One of the two plants with unexpected chromosome constitutions had 2n=42 chromosomes including the cylindrica chromosome, and the other had 41 whole chromosomes and a small telocentric one. Therefore. the cylindrica chromosome was confirmed to be transmitted to 17 plants out of 19. When the monosomic addition line was self-pollinated, almost all offspring (20 out of 22) were disomic addition plants with 2n=44 chromosomes including a pair of the cylindrica chromosomes. One of the unexpected chromosome constitutions was 2n=45 including a pair of the cylindrica chromosomes, and the other was 2n=44 including two cylindrica chromosomes plus an aberrant chromosome with a subterminal centromere which was smaller than the cylindrica chromosome. The results shown in Table 2 suggested that the cylindrica chromosome had been transmitted exclusively through egg cells and pollen. The unexpected chromosome constitution might have originated from the unstable chromosome pairing of the monosomic addition line. |
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