Haploid and Twin Formation in a Wheat Strain Salmon with Alien Cytoplasms

抄録

In order to elucidate the developmental mechanism underlying the frequent formation of haploids and twins in a nucleus-substitution line of a common wheat Salmon (2n=42), several experiments were carried out with the following results:
1. Salmon's nucleus was placed by repeated backcrosses into the three alien cytoplasms of Aegilops caudata, Ae. ovata and Triticum timopheevi, and the occurrence of haploids and twins was investigated in the three nucleus-substitution lines (indicated by (caudata)-Salmon, (ovata)-Salmon and (timopheevi)-Salmon) and a normal line of Salmon. Both haploids and twins were frequently found only in (caudata)-Salmon; Ae. caudata cytoplasm was evidently different in this regard from the other cytoplasms employed.
2. In (caudata)-Salmon, parthenogenetic embryos were found in 29.8 per cent of ovules, which remained non-pollinated and were fixed six to nine days after emasculation, while 29.4 per cent of plants obtained from pollination delayed for five to nine days after emasculation were haploid. This fact indicates that haploid formation in this material is mainly due to haploid parthenogenesis of the egg cell.
3. Frequency of twin seedlings was on the average 6.5 per cent, most of them being of haplo-diplo type. Embryological studies of non-pollinated and delayed pollinated ovules as well as cytological and morphological studies of twin seedlings revealed that parthenogenetic development of the egg cell, followed by fertilization of one of the synergids is the main mechanism of the formation of twin embryos; fertilization of a synergid was taking place in about 24 per cent of ovules, whose egg cell had developed parthenogenetically.