| The alien chromosome substitution line of durum
Wheat II. Substitution of the chromsome e7 of Agropyron elongatum
for the chromosome 4A of Triticum durum cv. Stewart Hisashi TSUJIMOTO Laboratory of Genetics, Faculty of Agriculture, Kobe University, Kobe A monosomic substitution line of Agropyron elongatum chromosome e7 designated by Mochizuki (1962) for the chromosome 4A of Triticum durum cv. Stewart was produced by crossing monosomic 4A of durum wheat [2n=27, (AABB)-4A] as a female with disomic addition line of e7 chromosome [2n=30, (AABB)+e7e7] as a male. This monosomic substitution [2n=28, (AABB)-4A+e7] is morphologically distinct different from normal durum wheat by observing number of tillers, thickness of culm and length of awn. There is, however, no significant difference in plant height between the substitution and the euploid durum. The plants of the monosomic substitution grew vigorously, but had reduced fertility. This is presumably due to the presence of two univalents at meiotic metaphase I (Table 1). The transmission rate of chromosome e7 through pollen grains was determined by crossing this monosomic substitution line as a male with durum wheat. From the number of the F1 plants with 13"+2' at meiotic metaphase I, the male transmission rate of chromosome e7 of Agropyron was 38.8%. Considering the facts that the competition takes place generally between the euploid and the substitution pollens in fertilization and that the nullisomic 4A pollens[(AB)-4A] do not participate in fertilization, this value implies that chromosome e7 fairly well compensates for the lack of chromosome 4A. The female transmission rate of the alien chromosome e7 determined from the reciprocal cross was unexpected high as shown in Table 2. The observed frequencies of 7 types of chromosome constitution derived from the selfed progeny of monosomic substitution e7 (4A) were in agreement with the expected frequencies of those estimated from the data of male and female transmission rates bf chromosome e7. Among the plants having 27 chromosomes obtained from self-pollinated monosomic substitution e7(4A), two types were recognizable from their awn length. One was almost the same as monosomic 4A and the other had shorter awn than that of monosomic 4A. The plants with short awn was mononullisomic e7 (4A), [2n=27, (AABB)-4A4A+e7]. In this case, single dose of chromosome e7 of Agropyron sufficiently compensates for double doses of chromosome 4A. According to cytological observation, the PMCs of monosomic substitution e7(4A) had 2 univalents, but cells with 14" were not observed at meiotic metaphase I. At diakinesis, however, majority of PMCs had 14", suggesting homoeologous pairing between 4A and e7. From the results, it seems that Agropyron chromosome e7 is related to the homoeologous group 4, i.e., the e7 chromosome might be considered as 4E. |