| In the various hexaploids synthesised from different tetraploid wheats
and Ae. squarrosa varieties, the percentage florets which yielded
viable kernels when crossed with diploid rye ranged from 1.24% to 24.74%
(Table 2). Similarly the precentage florets of
the natural hexaploids (bread wheats) which produced viable hybrid kernels
ranged from 1.66% to 39.80% (Table 2). This wide
range in both the synthesised hexaploids and bread wheats is due to genetic
variability that affects crossability and the viability of the hybrid kernels.
Kernel set ranged from 6.12% to 50.0% in the synthesised hexaploids, and
from 8.33% to 71.2% in the bread wheats, whereas the viability of the hybrid
kernels ranged from 6.38% to 73.24% in the synthesised hexaploids, and from
13.58% to 80.0% in the bread wheats (Table 2).
The D-genome not only affects the germinability of the wheat x rye hybrid kernels, but also appears to have an effect on the crossability of wheat with rye. The tetraploids, T. durum, T. dicoccum and T. carthlicum, produced a significantly (at 1% level) larger number of hybrid kernels than their synthesised hexaploid counterparts (Table 2). This may be due to the operation of a weak Kr-system in the D-genome as suggested by KROWLOW (op. cit.). The crossability with rye of various wheat species and cultivars, with special reference to the Kr-system, is discussed in a separate paper (MARAIS and PIENAAR, 1976). The cytoplasm of 6x breads wheats appears to have no effect on the development of wheat x rye hybrid kernels. In Table 2 it can be seen that the F1 kernels resulting from the Tetra-Canthatch (with 6x cytoplasm) x rye crosses are as inviable as those produced by the crosses involving the normal tetraploid wheats - none of the 25 Tetra - Canthatch x rye hybrid kernels that were obtained, germinated. Acknowledgments We wish to thank Dr. E.R. KERBER, Canada Department of Agiculture, Winnipeg, Manitoba, Canada, for most of the material listed in Table 1. Literature Cited KATTERMANN, G. 1941. Ueber heterogenomatische amphidiploides Weizenroggenbastard. Z. Pflanzenzuchtung. 23: 179-209. KERBER, E.R. and G.G. ROWLAND 1974. Origin of the free threshing character in hexaploid wheat. Can. J. Genet. Cytol. 16: 145-154. KROWLOW, K.D. 1964. Kreuzungen zwischen tetraploiden Weizen der Emmerreihe und 4n-bzw. 2n-Roggen in Verbindung mit Embryotransplantationen. Z. Pflanzenzuchtg. 51: 21-46. KROWLOW, K.D. 1970. Untersuchungen uber die Kreuzbarkeit zwischen Weizen und Roggen. Z. Pflanzen-zuchtung. 64 : 44-72. KROWLOW, K.D. 1973. 4x-triticale, production and use in triticale breeding. Proc. 4th Int. Wheat Genet. Symp., Columbia. Mo. 237-243. KRUSE. A, 1974. An in vivo/vitro embryo culture technique. Hereditas 77: 219-224. LEIGHTY, C.E. and W.J. SANDO 1928. Natural and artificial hybrids of a chinese wheat and rye. J. Heredity 19: 23-27. MARAIS, G.F. and R. DE V. PIENAAR 1976. Hybridisation between wheat and rye. I. Variations in the frequency of kernels set. Agroplantae. (In press). MELNYK, J. and J. UNRAU 1959. Pairing between chromosomes of Aegilops squarrosa L. var. typica and Secale cereale L. var. prolific. Canad. J. Genet. Cytol. 1: 21-25. OEHLBR, E. 1931. Untersuchungen uber Ansatzverhaltnisse, Morphologie und Fertilitat bei Weizen- Roggen bastarden. Z. Pflanzenzuchtung. 16: 357-393. PIENAAR, R. DE V. 1973. Methods to improve the gene flow from rye and wheat to triticale. Proc. 4th Int. Wheat Genet. Symp., Columbia, Mo. 253-258. ROMMEL, M. 1958. Eine vereinfachte Methode der Embryokultur bei Getreide. Zuchter 28: 149-151. ROMMEL, M. 1960. The effect of embryo transplantation on seed set in some wheat-rye crosses. Can. J. Plant Sci. 40: 388-395. |
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