Formation of Haploids by Means of Delayed Pollination in Triticum monococcum

Abstract

A strain of Triticum monococcum L. var. vulgare KÖRN. gives rise to about 0.5% haploids under natural conditions. The percentage may be increased to 13.66% if the pollen is treated by X-rays before pollination (Tab.1).
The same strain was used to investigate the effect of delayed pollination in the production of haploids.
The pollen used for this investigation was taken from T. aegilopoides and the offspring of the hybrid T. aegilopoides×T. monococcum. The pollen parent posessed always dominant genes for hairs on the leaves. The emasculation was made in the young florets, which, it was estimated by the control spikes, would open 3-4 days later.
No haploid individual was produced from the pollination made on the 2nd and 5th day after emasculation. Pollination, which was carried out later, was successful. The highest percentage of haploid formation was obtained from a delayed pollination of 9 days (Tab.2 and Fig.1).
The seeds, from which haploids are produced, have normal endosperm. The haploids were always mother-like notwithstanding dominant genes from the pollen parents.
The microscopical investigations of KATAYAMA (1933) show that many celled embryos may be found in the ovaries on the ninth day after emasculation. Without endosperm these ovaries seem not to develop further. The present author could riot obtain any seeds from the emasculated forests, which were left unpollinated.
From these results, it may be concluded that normal double fertilization does not take place owing to delayed pollination. However the triple fusion of the pole nuclei and the sperm nucleus is realized and the endosperm is formed accordingly.
The egg cells develop parthenogenetically into the haploid embryos, if the ovules are left unpollinated after emasculation. The formation of haploid embryos seems to begin from the sixth day after emasculation.
The rôle of the unfertilized sperm nucleus as a stimulating agency in the parthenogenesis of egg cells was not taken into consideration. No haploid individual was found in the F2- and F3-progenies of the hybrid between T. monocoecum×T. aegilopoides (Tab. 3).
Twin seedlings were never found in the progeny of T. monococcum on selfing or on open pollination. They are, however, frequently found in the seedlings obtained from cross pollination (0.78%). The percentage was very high in the case of delayed pollination. 3 pairs of twins were found among 195 seedlings.