Hybrid dwarfness in crosses between wheat (Triticum aestivum L.) and rye (Secale cereale L.): a new look at an old phenomenon.

The existence of hybrid dwarfs from intraspecific crosses in wheat (Triticum aestivum) was described 100 years ago, and the genetics underlying hybrid dwarfness are well understood. In this study, we report a dwarf phenotype in interspecific hybrids between wheat and rye (Secale cereale). We identified two rye lines that produce hybrid dwarfs with wheat and have none of the hitherto known hybrid dwarfing genes. Genetic analyses revealed that both rye lines carry a single allelic gene responsible for the dwarf phenotype. This gene was designated Hdw-R1 (Hybrid dwarf-R1). Application of gibberellic acid (GA3 ) to both intraspecific (wheat-wheat) and interspecific (wheat-rye) hybrids showed that hybrid dwarfness cannot be overcome by treatment with this phytohormone. Histological analysis of shoot apices showed that wheat-rye hybrids with the dwarf phenotype at 21 and 45 days after germination failed to develop further. Shoot apices of dwarf plants did not elongate, did not form new primordia and had a dome-shaped appearance in the seed. The possible relationship between hybrid dwarfness and the genes responsible for the transition from vegetative to generative growth stage is discussed.

[Genetics of anthocyaninless rye].

Six nonallelic genes have been discovered in rye, the recessive mutations of which lead to a lack of anthocyanin. Crosses with these mutants showed that 13 new anthocyaninless lines carry mutations in the gene vi1, whereas vi2/6 mutations were identified only in single cases. Inheritance of the vi1/6 mutations in the progeny of hybrids with the wild type (Line 7, L7) corresponds to a monohybrid segregation. Segregation for three of these mutations (vi2, vi4, and vi5) in hybrids with line 2 is characterized by anthocyaninless deficiency in plants. We discuss the reasons for such deviations and the previously published data for the identification of the six anthocyanin pigmentation genes in the rye using trisomic analysis.

Genetic studies of self-fertility in rye (Secale cereale L.). 1. The identification of genotypes of self-fertile lines for the Sf alleles of self-incompatibility genes.

Segregation for self-fertility has been studied in progenies from the crosses of self-sterile (SS) plants with interline hybrids obtained by a diallel scheme of pollinations between seven self-fertile (SF) lines (nos. 2-8) and with F1 (SS plant x SF line) hybrids. All the offspring families from the SS plant x F1 (SS plant x SF line) crosses demonstrated a 1SF∶1SS segregation. The crosses of SS plants with some interline hybrids gave only self-fertile plants, whereas the crosses with other interline hybrids gave a segregation of 3SF:1SS expected in the case of digenic segregation. The data obtained permitted us to identify three different S loci (S1, S2, S5) and to estimate the genotypes of self-fertile lines for their Sf alleles: lines 5, 6, 7 and 8 are S1f/S1f S2n/S2n S5m/S5m, line 4 is S1n/S1n S2f/S2f S5m/S5m, and lines 2 and 3 are S1n/S1n S2m/S2m S5f/S5f(Sn, Sm designate active alleles of the incompatibility genes). The identification of the particular S gene which is presented by the Sf allele in each line has been made on the basis of our data concerning the linkage of the Sf mutation with isozyme markers of particular rye chromosomes, which is reported in an accompanying paper.

Genetic studies of self-fertility in rye (Secale cereale L.). 2. The search for isozyme marker genes linked to self-incompatibility loci.

The segregation of several isozyme marker genes has been studied in F2 inbred families from hybrids between self-sterile and five self-fertile inbred lines (nos. 2, 3, 4, 5, and 8) as well as from interline hybrids. Self-pollination of F1 hybrids between self-sterile forms and lines 5 and 8 gave an F2 segregation ratio of 1 heterozygote:1 homozygote for the gene Prx7 (chromosome 1R) against the allele from the line. This is interpreted as a result of tight linkage of the Prx7 gene with the S1 gene in chromosome 1R (recombination at a level of 0-1%). The self-pollination of such hybrids with lines 2,3 and 4 gave normal segregation for the Prx7 gene (1:2:1). This means that these lines carry a self-fertility allele which is not on chromosome 1R. Interline hybrids 5×2, 5×3 and 5×4 had self-fertility alleles for the two S genes and in inbred F2 progenies gave the expected deviating segregation for the Prx7 gene in a ratio of 2:3:1. The segregation of interline hybrid 5×8 was normal, 1:2:1, as expected. Highly-deviating segregation in an inbred F2 family of a hybrid with line 5 has also been obtained for another gene from chromosome 1R - Pgi2 (recombination with the S1 locus of 16.7%). By using the same method it has been estimated that line 4 has a self-fertility allele of the S2 locus from chromosome 2R and that the genes ß-Glu and Est4/11 are linked with it (recombination 16.7% and 17.5-20% respectively). Lines 2 and 3 have a self-fertility allele of the S5 locus from chromosome 5R which is linked with the Est5-7 gene complex (recombination at a level of 28.8-36.0%).