| 1. Seed setting and germination in F1 generation: The average seed setting (12.32 percent) and germination (42.60 percent) of the F1 hybrids involving monosomic series of Pb C 591 x Bijaga Yellow was low compared to disomic Pb C 591 (Table 1). In disomic cross it was 22.58 percent and 67.86 percent respectively. None of the crosses involving monosomic lines of Pb C 591 x Bijaga Yellow showed better seed setting with high germination. This may be due to the monosomic condition of female parent when crossed with tetraploid Bijaga Yellow where there will be greater imbalance of the proportion of chromosomes for the development of embryo and endosperm. Because of the incompatibility of female and male gametophytes, fertilization does not occur, even if there is a fertilization, the embryo aborts during its developmental stages. Seed setting was drastically affected in the crosses involving 6A, 1B, 3B, 4B, 5B and 6B with Bijaga Yellow. MOKHTARZADEH (1975) reported the chromosomes 1A, 2A, 7A, 1B, 4B and 6B to carry genes which promote seed setting and in the absence of these chromosomes significant reduction in seed setting was observed. In the present investigation, germination was reduced drastically in crosses involving the chromosomes 1A and 2A in monosomic condition with Bijaga Yellow. Failure to obtain viable seeds could largely be due to abnormal chromosome relationships between embryo and endosperm (STEBBINS 1958), and the dosage of genes and genomes in the endosperm. In addition, deleterious effects of genes located on chromosomes 1A, 2A, 4A, 5A, 6A, 7A, 1B, 4B and 7B in the corresponding Bijaga Yellow could probably be the prime cause of the observed zygotic lethality. The same factors might have been the cause of zygotic lethality in the interspecific hybrids observed previously (THOMPSON & HOLLINGSHEAD 1927, WATERHOUSE 1933, 1952). 2. Seed setting and germination in first back cross generation The average seed setting (10.46 percent) and germination (43.48 percent) was lower than the control hybrid i .e. disomic hybrid or eupentaploid (Table 2). It may be concluded that all chromosomes from the A and B genomes of Bijaga Yellow except the chromosome 3B influenced the seed setting of the interspecific hybrids. But SEARS (1954) found all the chromosomes including 3B in common wheat to influence fertility. The decreased seed set in the present investigation may be due to the presence of major promoter genes for seed setting of the back cross progeny. The presence of all chromosomes carrying the major or minor promoter genes for seed setting may collectively have a complementary epistatic effect on the suppressor genes and result in relatively high seed set of the pentaploid hybrids. MOKHTARZADEH (1975) reported chromosomes 1A, 1B, 4B and 6B to carry genes with major effects for the promotion of seed setting and 4A, 2B, 6A and 7B to carry inhibitary genes. |
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