Agricultural Genetics Center, Hanoi, Vietnam
The study of chromosome number and karyomorphology in rice was first carried out by Kuwada in 1910. Later, this work was followed by several authors (Hu 1964; Chu 1967; Khan 1975; Kurata and Omura 1978; Kurata et al. 1981). However, disagreement on several points existed especially the number of chromosomes with satellites.
We used a relatively simple method based on differential staining of pachytene and prometaphase chromosomes. This method permitted us to analyze rapidly the chromosome number and karyomorphology and structural characteristics of each chromosome.
We germinated the seeds at 28°C. When the radicle was 1.5-2cm. long. it was removed from seed and treated with saturated anpha bromnaphthalene at 5°C for 4-5 hours. It was then fixed in 1:1 mixture of ethylene alcohol 96% and glacial acetic acid for 12-18 hours. Before staining in 3% acetocarmine, the radicle was macerated in 1 N HCl at 60°C for 5-10 minutes, or in 5% pectinase mixture (pH 3 to 3.5) at the laboratory temoperature for 72 hours.
In the rice variety we studied, only one pair of chromosome had satellite and this agreed with the results of Kurata and Omura (1978), Chu (1967) and Khan (1975).
One may use this differential staining technique to study the altered karyotypes after treatment with mutagenic agents as well as the karyotype evolution of different species in genus Oryza.
Kuwada, Y. 1910. Cytological study of Oryza sativa L. Bot. Mag. Tokyo, 24: 267-287.
Hu, C.H., 1964. Further studies on the chromosome of O. sativa L. In Rice genetics and cytogenetics, Elsevier, Ansterdam p. 51-61.
Chu, Y.E., 1967. Pachytene analysis and observations of chromosome associaion in haploid rice. Cytologia, 32: 82-95.
Khan, S.H., 1945. A technique for staining rice chromosome. Cytologia 40: 595- 598.
Kurata, N. and T. Omura, 1978. Karyotype analysis in rice. I. A new method for identifying all chromosome pairs. Japan J. Genetics. 53: 251-255.
Kurata, N., T. Omura and N. Iwata, 1981. Studies on centromere, chromomere and nucleolus in pachytene nuclei of rice Oryza sativa L. Cytologia 46: 791-800.