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According to MUNTZING (1933), disturbances in endosperm development frequently result from deviations of the normal ratio between chromosome numbers of the maternal tissue, the endosperm and the embryo (2 : 3 : 2). This assumption was based on the observation that the parent with a higher chromosome number, used as a female, yielded the better seeds. In Table 2 the ratios of the chromosome numbers in our hybrids are compared with those of the respective species. The deviation of the crosses Nos. 1-4 from the normal chromosome ratio does, however, not correspond to the percentage of shrivelled seeds, as given in Table 1. For example, there were 4.2 per cent of poor seeds in cross No. 1 and 82.7 per cent in cross No. 3, both of which showed almost the same chromosome ratio between endosperm and embryo (1.75 and 1.80, respectively).

This problem can be solved, if the comparison is not based on the chromosome number as such but on the number of the different wheat and rye genomes in the endosperm itself. It can be seen that in the amphidiploid hybrids, both yielding perfect seeds, 9 wheat and 3 rye genomes each with 7 chromosomes are combined in the endosperm. Wherever this ratio decreases, the endosperm developement is inhibited (cf. cross Nos. 2 and 3), but an equal deviation in the opposite direction does not cause similar disturbances (cf. cross Nos. 1 and 4). This leads to the conclusion that specific interactions between the wheat and rye genomes combined in the hybrid endosperm are responsible for normal endosperm development.

Cytological investigations of the various hybrids were made. In 51.7 per cent of the Secalotricum and in 55.7 per cent of the Triticale pollen mother cells, no pairing of the 28 chromosomes was observed in metaphase I. On the average of 170 cells of the Secalotricum haploids 26.2 univalents and 0.92 bivalents and in 140 cells of the Triticale haploids 26.1 univalents and 0.94 bivalents were counted. From these results it can be concluded, that the different cytoplasm does not affect the pairing of the chromosomes in the reciprocal hybrids, [r] RW and [w] WR, resp. The observations of this study are not in favour of a pairing between rye and wheat chromosomes; the observed bivalents appeared to result from autosyndesis of the wheat chromosomes only. A detailed description of the experiments is given by SMUTKUPT (1968).

Literature

FIRBAS, H. 1920. Uber die Erzeugung von Weizen-Roggen-Bastardierungen. Z. f. Pflanzenzucht 7 : 249-282.

KARAPETIAN, V.E. 1966. Genetical analysis of rye-wheat and wheat-rye hybrids. Proc. 2nd Int. Wheat Genetics Symp., Lund 1963. Hereditas. Suppl. Vol. 2 : 467-468.

MUNTZING, A. 1933. Hybrid incompatibility and the origin of polyploidy. Hereditas 18 : 13-55.

SMUTKUPT, S. 1968. Herstellung und Eigenschaften von Secalotricum im Vergleich mit Triticale. Angew. Botanik 42 (in press).

TSCHERMAK-SEYSENEGG, E.v. 1933. Uber einige bei reziproker Kreuzung nur selten gelingende Bastarde. Zuchter 5 : 123-128.

(Received March 4, 1968)



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