| In the present study, seed setting was drastically reduced in the crosses
involving parents with monosomic condition for 2A, 3A, 6A, 4B, 5B, 6B and
7B and better seed setting was observed in crosses involving monosomics
for 1A, 4A, 5A, 7A, 2B and 3B. Disturbance in the seed setting of the interspecific hybrids may be expected as a result of interactions between A and B genomes originating from different sources (PISSAREV 1966). In addition, the absence of chromosomes influencing fertility and crossability may reduce significantly the fertility of the monopentaploid hybrids. Loss of chromosomes carrying genes which promote or suppress fertility can be revealed by very low or very high fertility in the monopentaploid plants when compared with the average of the monosomic lines (BOZZINI & GIORGI 1971). Based on the results of the present experiment, chromosomes 2A, 3A, 1B, 4B, 5B and 6B in Bijaga Yellow can be considered as the carriers of promoter genes for seed fertility. The cytoplasmic effect of the hexaploid parent in reducing the hybrid fertility has already been ruled out (KIHARA 1968, SUEMOTO 1968). In the present study reduction in seed germination was confined to lines 6A, 2B, 6B and 7B. This may be due to abnormal chromosome relationships between embryo and endosperm. 3. Seed Setting and germination in second back cross generation: As in case of F1 and BC1 generations, in second backcross generation also, seed setting was poor, particularly in lines 2A, 3A, 4A, 2B, 4B, 6B and 7B seed setting was very less. It seems chromosomes 2A, 3A, 4A, 2B, 4B, 6B and 7B in Bijaga Yellow carry genes which promote seed setting. Seed germination was increased in second back cross generation. This may be due to the following reasons, when plants with 13"+2' were crossed to Bijaga Yellow, 72.81 percent of the plants obtained by this cross were found to be disomic for A and B genomes (14") (Table 3). So, most of the 13"+2' plants may be producing 14 chromosome female gamete and when this gets fertilized with Bijaga Yellow pollen (n=14), there will be normal seed setting, because of the absence of variation in chromosome number. 4. Seed setting and germination in thrid back cross generation: In third back cross generation in monosmic lines 3A, 4A and 6B, seed setting was reduced compared to other lines (Table 4). This was also observed in F1, BC1 and BC2 generations. This may mainly be due to the presence of promoter genes for seed setting on chromosomes 3A, 4A and 6B in Bijaga Yellow and the absence of these chromosomes has drastically reduced the seed setting. |
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