31. Cytological identificaiton of extra chromosome in trisomics and location of the brittle-culm (bc) gene

There trisomic lines, R78-14-8, R77-16-3 and R77-24-2, made available through the courtesy of the International Rice Reseach Institute, were investigated by using the new technique for root-tip chromosomes developed by Kurata and Omura (1978). The extra chromosomes embodied in the trisomic lines were chromosomes X, VII, and IV, respectively; the chromosomes were numbered according to their length in descending order. R77-16-3 had two pairs of nucleolar chromosomes. This confirmed Liou's analysis of pachytene chromosomes.

Each of the three trisomic lines were crossed to six marker stocks carrying d-1 (Daikoku dwarf), Dn (dense panicle), lg (liguleless), gl (glabrousness), g (long empty glume), and bc (brittle culm), respectively. Since the F\1\ plants had a low fertility due to the effect of an extra chromosme and Indica (trisomic) x Japonica (marker) crosses, only 6 cross-combinations yielded F\2\ populations large enough for studying segregation ratios. One of them, R77-16-3 x bc, gave a ratio significantly deviating from 3:1 and fitting the trisomic ratio. This indicated that bc was located on chromosome VII.

Kurata, N. and T. Omura, 1978. Karyotype analysis in rice, 1. A new method for identifying all chromosome pairs. Jpn. J. Genet. 5: 251-255.

Liou, H. C., 1983. Cytogenetics of rice trisomics. MS thesis submitted to National Taiwan University, Taipei.