24. Genetic analysis of "cybrids" produced by asymmetric fusion between O. rufipogon (cytoplasm donor) and O. Sativa

Toshiro KINOSHITA, Kohichi MORI and Itsuo TAKAMURE

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
R1 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.

There was a novel male sterility (RU-51) system induced by the combination of W124 cytoplasm and Kitaake nucleus. In addition, line RU-75 indicated a spreading plant type, purple apiculus color and red seed coat which are identical with those of W124, while awn length and spikelet shape were intermediate between both parents (Fig. 1).

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 mutation 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 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. 1. Plant type (a), spikelets (b) and kernels (c) of O. rufipogon, W124 (left), the variant RU-75 (middle) and Kitaake (right).

 

Fig. 2. Graphical genotype of the variant, RU-75, showing the derivatives from O. rufipogon (W124) and from Kitaake, and novel parts.

References

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.