IARI
B chromosomes and abnormal chromosome 10 (K10) in northeastern Himalayan maize
--M. Kumar and J. K. S. Sachan
The presence of B chromosomes in certain maize stocks is of worldwide distribution. B chromosomes have been found floating in the population due to non-disjunction and preferential segregation.
In contrast to the wide distribution of the abnormal chromosome 10 (K10) in different American races, it was reported to be completely absent from Asia and Europe. However, recently the presence of this abnormal chromosome 10 in higher frequency in local maize of Kashmir, India, has been reported (Jotshi and Patel, MNL 58, 1984).
Altogether, 66 maize collections from different areas of the northeastern Himalayas, including Arunanchal Pradesh, Assam, Meghalaya, Nagaland, Tripura, Sikkim, W. Bengal and Nepal, were screened for the presence of B chromosomes and abnormal chromosome 10. Emerging tassels were fixed in a mixture of ethanol-glacial acetic acid (3:1) and were stored at 4±1 C. PMCs were analysed at pachytene for the presence of K10 and at diplotene-diakinesis for B chromosomes. Further later stages were observed for studying the behaviour of B chromosomes during metaphase I and anaphase I.
B chromosomes were found in 9 out of 66 collections studied. The collections possessing B chromosomes include two from Assam, three each from Sikkim and Nagaland and one from Tripura (Table 1). Collections from Assam (AS-59, AS-60) and Sikkim (S-21, S-24 and S-59) had 1-2 B's. Nagaland collections (N-24, N-29 and N-44) had 1-3 B's and the lone Tripura collection possessing B chromosomes (2 B's) was T-17. On the other hand, B chromosomes were found to be totally absent in collections from Arunanchal Pradesh, West Bengal, Meghalaya and Nepal (Table 1).
Table 1. Distribution of abnormal chromosome 10 (K10) and B chromosomes
in NEH maize.
| Region | No. of collections observed | No. of plants analysed | Total collections with K10 | Total collections with B's | Total plants with B's | Average B's/plant |
| Assam | 3 | 15 | - | 2 | 8 | 1.25 |
| Arunanchal Pradesh | 2 | 10 | - | - | - | - |
| West Bengal | 1 | 4 | - | - | - | - |
| Meghalaya | 15 | 73 | - | - | - | - |
| Nagaland | 13 | 62 | 1 | 3 | 9 | 1.33 |
| Sikkim | 18 | 87 | - | 3 | 11 | 1.18 |
| Tripura | 13 | 64 | 1 | 1 | 3 | 2.00 |
The presence of B chromosomes in Indian maize has been reported by some earlier workers also (Jotshi and Patel, 1984; Sarma and Sharma, 1986; Venkateswarlu, 1965). However, there is still only one report of B chromosomes in a maize collection from the Naga Tribe (Venkateswarlu, MNL 39, 1965).
The presence of an abnormal chromosome 10 (K10-I) was a rare event in NEH maize collections, being present in only two collections, namely N-37 and T-17 from Nagaland and Tripura respectively.
Thus, varying frequency of B chromosomes was observed in NEH maize strains,
and its geographical distribution was not as limited as that of K10. This
is the first report of the presence of K10 in NEH maize collections.
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