| Results and Discussion Monosomic lines of Pb C 591 which were used as female parents in the present investigation would produce either 'n' or 'n-1' gametes in different proportions. As the transmission of monosomic condition from female side in hexaploid wheat is about 75 percent, 75 percent of the monopentaploid plants are expected when crossed with a tetraploid Bijaga Yellow. But in the present investigation only 52.51 percent of the plants were monopentaploids (Table 1). This may be due to reduced viability or inviability of n-1 spores or reduced viability of 2n-1 zygotes. Occurrence of the monopentaploid condition (81.82 percent) occurred in 5D and minimum was seen in line 2D. This may be due to differential transmission rate of monosomic condition to its progeny. BOZZINI & GIORGI (1971) also observed such variability in transmission rates of monosomic condition in different A and B genome lines. ALSTON & JONES (1968) studied the breeding behaviour of monopentaploid plants when back crossed to T. durum. In the BC1 progeny they observed 57 percent of the plants with 28 chromosomes and 23 percent of the plants with either 29 or 30 chromosomes. In the present investigation, in the first back cross generation of monophentaploids x Bijaga Yellow, it was observed that the percentage of plants with 28, 29 and 30 chromosomes was 29.95, 5.88 and 27.81 respectively (Table 2). In all the D-genome lines, frequencies of plants with haplosomic condition (14"+1') occurred in lesser frequency, the range being 3.23 percent to 9.25 percent. Same observations were made by ALSTON & JONES (1968). In the progenies of eupentaploids when back crossed to Bijaga Yellow, 40 percent of the plants were observed to be with 28 chromosomes, whereas only 5 percent of the plants had 29-chromosomes. Plants with 30 chromosomes were about 20 percent. ALSTON & JONES (1968) also observed the same frequencies. They noticed 49 percent of plants with 28-chromosomes and 28 percent with 29 or 30 chromosomes. YAMASHITA (1947) and MATSUMURA (1952) isolated seven haplosomics representing each of the D-genome chromosomes from a Triticum spelta (2n =42) x T. polonicum (2n =28) pentaploid hybrid. MATSUMURA (1961) was able to maintain his lincs as diplosomics (2n = 30) selected from the progeny of each haplosomic line. OPEKE (1961) studied the haplosomic lines from pentaploid hybrids of T. aestivum x T. durum and of T. aestivum x T. dicoccum but was not able to maintain them as diplosomics. However, he suggested that it might be possible to maintain them if the tetraploid complements were more homozygous. In the present investigation, in the second back cross generation in general, plants with 29-chromosomes (14"+1') were observed in less frequency (8.69 percent) compared to disomics (91.31 percent) (Table 3). In third back cross generation (Table 4) also, the transmission frequency of haplosomic condition to its progeny was quite low (3.84 percent). The range was from 3.44 percent to 6.97 percent. |
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