Cytological Studies of Sugarcane and its Relatives
XV. Basic chromosome number of Saccharum officinarum L
1959 年 24 巻 2 号 p. 220-236
詳細
1959 年 24 巻 2 号 p. 220-236
The euploid number of Saccharum officinarum L. is 80. By crossing noble cane variety vellai (2n=80) to Sclerostachya fusca A. Camus (2n=30), and by repeated back-crossing to the recurrent male parent, the chromosomes of sugarcane will be halved in each successive back-cross generation. Till finally, in the third back-cross generation only 10 sugarcane chromosomes are left in the hybrid along with 30 Sclerostachya-Narenga chromosomes. The third back-crossing was done in Taiwan. Narenga Porphyrocoma (Hance) Bor (2n=30) was used instead of Sclerostachya.
SG310/6 (BC1) was found to have 72 chromosomes, 42 of which belong to sugarcane, the other 30 to Sclerostachya. It was obtained by back-crossing F1 hybrid to Sclerostachya. Of PMC's examined, many had 36 bivalents showing complete autosyndesis. The larger closed-type bivalents of Sclerostachya can be easily distinguished from the smaller open-type ones of sugarcane. One or two tetravalents were formed by the sugarcane chromosomes.
In the second back-cross generation, clone SG363/4 was found to have 50 chromosomes. In majority of the cases, 25 bivalents were found. Again it showed complete autosyndesis. One sugarcane tetravalent was found sometimes.
In the third back-cross generation, Narenga was used. 14 out of 15 plants were found to have 40 chromosomes. The other had 63. There was almost perfect pairing between the chromosomes of Sclerostachya and Narenga forming 15 closed type bivalents. The 10 sugarcane chromosomes remained either as univalents or as 1-4 open type bivalents. As many as 4 trivalents were found. It showed that 4 sugarcane chromosomes were partially homologous with 4 Sclerostuchya-Narenga chromosomes. Sometimes, two tetravalents were found. There were found to be composed of two sugarcane and two Sclerostachya-Narenga chromosomes.
From these, it is conjectured that the 10 sugarcane chromosomes are probably made up of two sets of 5. Four chromosomes of each set are partially homologous to one another. At least 4 chromosomes of one set of 5 of one species are partially homologous to 4 of those from either Sclerostachya or Narenga. Initial hybridization between two unidentified species with n=5 each leading to segmental allopolyploidy, and followed by two successive autopolyploidization, have probably resulted in the origin of S. officinarum with 80 chromosomes.
