Distribution of haploids on the ear
--K.R. Sarkar, B.M. Prasanna and P. Gayen
In a controlled pollination with silk trimming, the ovules at the bottom of the ear have longer silk length than those at the tip and the pollen tubes have to traverse a longer distance. Hence, there should be greater likelihood of getting haploids at the bottom half of the ear. In a survey of over 161 ears obtained from ACR x C-I, a haploidy-inducer line cross, this expectation was not realized. On the contrary, the tip half showed a haploid frequency of 7.49 percent (11739 kernels) as against 3.77 percent (11345) kernels in the bottom half. In a further study of the same cross, an additional 122 ears were longitudinally divided into three zones, top, middle and bottom, and the haploid cases were scored (Table 1). The results were interesting. While the top third of the ears always yielded the highest frequency (8.52%), there was no substantial difference between the middle (4.91%) and the bottom thirds (4.40%). However, some families showed higher frequencies at the bottom portion while others had more haploids in the middle zone. The same trend was also observed when one common male was used to cross on seven female cultures. The reasons behind such occurrences are not immediately clear; perhaps the sequence of fertilizations of ovules on the ear tip and differential silk factors are responsible for this uneven spatial distribution of haploidy cases on the cob. This observation will, however, help in further studies on the mechanism of the origin of haploids.
Table 1. Distribution of haploids in ears from ACR x C-I
crosses.
|
|
||||
| ACR culture | No. Ears | Top | Middle | Bottom |
| 6732 | 14 | 10.23 | 6.93 | 3.54 |
| 6733 | 9 | 14.93 | 10.93 | 7.04 |
| 6735 | 15 | 9.65 | 3.97 | 3.71 |
| 6736 | 15 | 8.94 | 4.91 | 4.16 |
| 6738 | 8 | 7.36 | 5.14 | 4.05 |
| 6744 D | 8 | 6.78 | 2.72 | 2.12 |
| Subtotal | 69 | 9.69 | 5.76 | 3.94 |
| 6666 | 12 | 5.95 | 2.63 | 5.01 |
| 6729 | 18 | 8.25 | 5.12 | 6.39 |
| 6734 | 17 | 5.92 | 3.46 | 4.39 |
| 6744 E.4 | 6 | 8.80 | 2.01 | 3.08 |
| Subtotal | 53 | 6.90 | 3.68 | 5.04 |
| Total | 122 | 8.52 | 4.91 | 4.40 |
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