Pachytene analysis in Oryza.

The karyomorphology of Oryza australiensis, O. glaberrima and O. stapfii was investigated at the pachytene stage. It was found that the twelve chromosomes of all the three species are identifiable by the lengths, arm ratios and chromomeric pattern. A detailed description of each of the bivalents is given. The bivalents of O. australiensis are considered to be more heterochromatic than those of the other two species. The present study indicated that the karyotypes of wild species, O. stapfii and O. australiensis, are more symmetrical than those of the cultivated species, O. glaberrima and O. sativa. The present study lends support to Nandi's hypothesis that the basic chromosome number of the genus is 5. The karyotype of O. australiensis is distinct by aggregation of chromomeres and the absence of supernumerary nucleoli. [ABSTRACT FROM AUTHOR]