I. Cytological studies

1. Establishment of a trisomic series in rice by using a desynaptic mutant

H. YASUI, H. SATOH and N. IWATA

Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka, 812 Japan

We have attempted to obtain trisomic plants by using a desynaptic mutant, MM 15, which was induced by a treatment of fertilized egg cells with N-methyl- N-nitrosourea (MNU) in the Japonica variety Kinmaze (Kitada and Omura 1983). Strain MM 15 is homozygous for a recessive desynapsis gene and nearly completely self-sterile. It was crossed with Kinmaze, and all F1 seeds obtained were sown on agar medium and the seedlings were transplanted in an experimental field. We examined morphological features of the F1 plants and screened for trisomics.

From crosses made in 1983 and 1986, we obtained 4,145 F1 seeds (Table 1). The crossability was 8 percent in 1983 and 16 percent in 1986. The F1 plants developed in 1982, 1983 and 1987 were classified into disomic (76.1%), trisomic (21.0%), double-trisomic (2.1%) and plants with other chromosomal aberrations including reciprocal translocation (0.8%) (Table 2). Possible twelve types of trisomic plants as judged from morphological features were obtained in the F1 population (Table 3; Iwata et al. 1970). They were each confirmed to have 25 chromosomes by cytological examination.

The trisomic series so far established in a Japonica (Iwata and Omura 1984) and an Indica rice variety (Khush et al. 1984) have been obtained by screening

Table 1. Cross- and self-fertilities of a desynaptic mutant MM15
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Pollination     Year  No. of spikelets   No.of         Fertility
                       pollinated      seeds set       (%)
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MM15 X Kinmaze  1983  31,054              2,507        8.1
MM15X Kinmaze   1986  10,558              1,638       15.5
MM15, open      1983  1,351                   6        0.5
MM15, bagged    1986  (No record)             0          0
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Table 2.Diploids and aneuploids found among the F1 plants from 
MM15 X Kinmaze
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Year  Diploid  Trisomics    Double-    Others  Total no.
                            trisomics          of plants
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1982     246    63 (20%)      4          0       313
1983      60    17 (22%)      0          0        77
1987     512   146 (21%)     18          9       685
Total    818   226 (21%)     22          9     1,075
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Table 3. Number and frequency (%) of each type of trisomics obtained in the
F1 plants from MM15 X Kinmaze
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Typea  
        Character nameb     1982     1983       1987      Total
                          No.  %    No.  %     No.  %    No.   %      
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A   Pale                  5   7.9   2   11.8   12  8.2   19  8.4
B   Awned                 4   6.3   1   5.9     6  4.1   11  4.9
C   Small grain           9   14.3  1   5.9    18 12.3   28 12.4
D   Erectoides            8   12.7  1   5.9    12  8.2   21  9.3
E   Spreading             7   11.1  0          21 14.4   28 12.4
F   Rolled leaf           7   11.1  4  23.4     4  2.7   15  6.6
G   Pseudo-normal         2   3.2   0          16 11.0   18  7.9
H   Large grain           9  14.3   2  11.8    20 13.7   31 13.7
L   Short panicle         9  14.3   3  17.6    13  8.9   25 11.1
M   Sterile               1   1.6   0           3  2.1    4  1.8
N   Smooth glume          0         2  11.8     5  3.4    7  3.1
0   Grassy                2   3.2   1   5.9    16 11.0   19  8.4
      Total              63 (100)  17 (100)   146(100)  226(100)
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a.  Corresponding to the type code given by Iwata et al.(1970).
b.   Corresponding to the name given by lwata and Omura (1984).
the progeny of crosses between autotriploid and diploid plants. In the present study, a new trisomic series was raised from the progeny of a desynaptic mutant. Such a desynaptic mutant is easily obtained by the MNU treatment of panicles (Kitada et al. 1983). These mutants are a useful source of trisomic plants. The desynapsis gene can be transferred to other varieties by hybridization.

References

Iwata, N., T. Omura and M. Nakagahara, 1970. Studies on the trisomics in rice plants (Oryza sativa L.), 1. Morphological classification of trisomics. Jpn. J. Breed. 20: 230-236.

Iwata, N. and T. Omura, 1984. Studies on the trisomics in rice plants (Oryza sativa L.), VI. An accomplishment of a trisomic series in japonica rice plants. Jpn. J. Genet. 59: 199-204.

Khush, G. S., R. J. Singh, S. C. Sur and A. L. Librojo, 1984. Primary trisomics of rice: Origin, morphology, cytology and use in linkage mapping. Genetics 107: 141-163.

Kitada, K., N. Kurata, H. Satoh and T. Omura, 1983. Genetic control of meiosis in rice, Oryza sativa L., I. Classification of meiotic mutants induced by MNU and their cytological characteristics. Jpn. J. Genet. 58: 231-240.

Kitada, K. and T. Omura, 1983. Genetic control of meiosis in rice, Oryza sativa L., II. Cytological analyses of desynaptic mutants. Jpn. J. Genet. 58: 567-577.