Plant Breeding institute, Faculty of Agriculture, Hokkaido University, Sapporo, 060 Japan
Protoplasts isolated from W124 (O. rufipogon) irradiated with gamma rays were electrofused with those from Kitaake after iodoacetoamide treatment. Several plants were regenerated, and their morphological characters and seed fertility were examined (Table 1). The transfer of cytoplasm from W124 to Kitaake was confirmed by Southern hybridization probed with B3, one of the plasmid-like DNAs involved in the mitochondrial genome.
Table 1. Characteristics of seven cytoplasmic hybrids produced from asymmetric protoplast fusion between O. sativa "Kitaake" and O. rufipogon, W124
=============================================================================== Parent Chro- Plant Awn Apiculus Empty Pistil Seed Seed Plasmid- or mosome type color glumes color coat ferti- like R\1\ plant number lity(%) DNA (B3) =============================================================================== Kitaake 24 Erect Awnless Green Colorless White White - O. rufipogon 24 Spreading Awned Purple Purple Purple Red + (W124) RU-7 24 Erect Awnless Green Colorless White White 19 + RU-12 48 Erect Awnless Green Colorless White White 0 - RU-13 24 Erect Awnless Green Colorless White White 4 + RU-39 48 Erect Awnless Green Colorless White White 4 + RU-46 24 Erect Awnless Green Colorless White White 33 + RU-51 24 Erect Awnless Green Colorless White White 0 + RU-75 24 Spreading Awned Purple Purple Purple Red 71 + =============================================================================== Note; +: Detected, -: Not detected.
According to RFLP analysis of RU-75 using the combinations between 93 probes and seven restriction enzymes, at least two RFLP markers were identical with those from W124 showing homozygosity as shown in the graphical genotype (Young and Tanksley 1989). As unique bands were reconginzed in six RFLP markers, there was a possibility that somaclonal variation or homozygous muta- tion occurred in several parts of chromosomes (Fig. 2).
Thus, the transfer of genes from O. rufipogon to cultivated rice was achieved in RU-75, although the genetic mechanism was unknown. However, there is
Fig. 1. Plant type (a), spikelets (b) and kernels (c) of O. rufipogon, W124 (left), the variant RU-75 (middle) and Kitaake (right).
also a possibility of somaclonal variation or mutation in the patterns of several RFLP markers. Detailed analysis is in progress by examining the progenies of RU-75.
Fig. 2. Graphical genotype of the variant, RU-75, showing the derivatives from O. rufipogon (Wl24) and from Kitaake, and novel parts.
Young, N.D. and S.D. Tanksley, 1989. Restriction fragment length polymorphism maps and the concept of graphical genotypes. Theor. Appl. Genet. 77: 95-101.