20. Survey of Oryza australiensis chromosomes in the backcross progeny of
  1. sativa x 0. australiensis by FISH 
Sakurako Uozu, Darshan S. brar, Gurdev S. khush and Kiichi fukui 1) Hokuriku National Agricultural experiment Station, Joetsu 943-01, Japan

2) International Rice Research Institute, P.O. Box 933, Manila, Philippines

3) Faculty of Agriculture, Kyoto University, Kyoto 606-01, Japan

 In situ hybridization is an effective method that can detect the localization of defined DNA sequences directly on rice chromosomes (Fukui et al. 1994; Ohmido and Fukui 1995). The use of the species-specific DNA sequences as probes enables us to monitor the alien chromosomes or chromosome fragments in the hybrids between different
Research Notes 83

Fig. 1. Mitotic metaphase chromosomes of the BC1F1 after hybridization between 0. sativa and 0. australiensis. a) Counter staining with DAPI, b) FISH signals of RIREI.
 

species. We investigated the chromosome composition of the backcross progenies of 0. sativa X 0. australiensis by fluorescence in situ hybridization (FISH) using the DNA sequences specifically abundant in 0. australiensis.

0. australiensis chromosomes have two characteristic features. They are more than twice as large as 0. sativa chromosomes, and the species-specific repeated DNA sequences (RIREI, Noma et al. 1996) are distributed on all the 0. australiensis chromosomes more or less evenly (Uozu et al. 1995). Therefore, it is possible to identify 0. australiensis chromosomes in the nucleus of the hybrid cell. Twelve large chromosomes of 0. australiensis were reasonably painted by the RIREI signals in the F1 between 0. sativa x 0. australiensis by FISH.

Twentyfive chromosomes consisting of 13 large and 12 small chromosomes were, however, detected in the BC1F1, the progeny of the F1 backcrossed with 0. sativa. Application of FISH unequivocally showed that the 13 large chromosomes were from 0. australiensis (Fig. 1), Twentyfive chromosome plants may have resulted from the fertilization between gametes with 12 0. sativa chromosomes and 13 0. australiensis chromosomes. The extra chromosome probably originated from the misdivision of an 0. australiensis chromosome during meiosis. It is concluded that species-specific sequences such as RIREI are useful to monitor the chromosome behavior during backcrossing.

References 

Fukui, K., N. Ohmido and G.S. Khush, 1994. Variability in rDNA loci in the genus Oryza detected through

fluorescence in situ hybridization. Theor Appl Genet 87: 893-899. Noma, K.., R. Nakajima, H. Ohtsubo and E. Ohtsubo, 1996. RIREI, a retrotranspuson from wild rice Oryza australiensis. Genes Genet. Syst. (submitted) 84 Rice Genetics Newsletter Vol. 13

Ohmido, N. and K. Fukui, 1995. Cytological studies of African cultivated rice, Oryza glaberrima. Theor

Appl Genet 91:212-217.

Uozu, S., T. Tanisaka, H. Ikehashi, H. Ohtsubo, E. Ohtsubo, D.S. Brar, G.S. Khush and K. Fukui, 1995. Analysis and utility of chromosome information 88. Survey of the Oryza australiensis chromosomes in the F1 and progenies of 0. sativa X 0. australiensis by FISH. Breed. Sci. 45(2): 108.