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Laboratoire d'Amelioration des Plantes, Centre ORSTOM d'Adiopodoume, BP V51, Abidjan, Cote d'lvoire
Four progenies of crosses between the two cultivated rice species were obtained by pollinating a common Oryza glaberrima/O. sativa F1 hybrid with four different 0. sativa cultivars. We present here the results on the development of these progenies and on the segregations scored at 6 isozyme loci.
The five parental varieties were: W025 (0. glaberrima, Guinea-Bissau), ES70-6 (japonica, Tanzania), YS309 and YS45-1 (japonica, Guinea), and SS404 (indica, Senegal). W025 was provided by the National Institute of Genetics (Mishima,Japan) while 0. sativa cultivars were obtained from ORSTOM collection. The 4 crosses studied are presented in Table 1. The F1 hybrid used as female parent W025/ES70-6 being common, the 4 crosses are designated as//ES70-6,//SS404,// YS45-1 and //YS309, respectively.
The seeds were dehulled, disinfected, rinsed in water and then sown in petri dishes with nutritive solution. After 10 days, seedlings were planted in pots. Plants were grown in glasshouse. Electrophoresis procedures used are described by Second (1982) and de Kochko (1987).
Approximately 40% of the plants were lost during cultivation (Table 1). The first level of loss was observed at seed germination. All progenies showed a similar rate of non-germinated caryopses (<20%), which was about the same as for F1 seeds of W025/ES70-6. The second level of losses occurred at seedling stage, where significant differences appeared between the progenies. More than 50% seedlings of the cross//ES70-6 died.
Table 1.Development of plants in four glaberrima/sativa//sativa
backcrosses
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No. of seeds No. of No. of Total
Cross ___________________ inviable adult percent
Non-germi-
Sown nating seedlings plants of loss
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W025/ES70-6//ES70-6 35 16(14%) 16(53%) 14 60%
"" //SS404 46 4(9%) 8(19%) 34 26
"" //YS309 12 2(17%) 1(10%) 9 25
"" //YS45-1 27 3(12%) 7(29%) 17 37
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Table 2 presents the results for segregation of isozyme loci. Note that
we have observed the segregations of the female gametes of the F1 hybrid
W025/ ES70-6. Four of the 20 observed segregations deviated (at 5%
significance level) from the 1:1 Mendelian ratio. The Est-2 locus was
subject to distortion in the crosses//SS404 and //ES70-6. Sdh-1 segregation
was abnormal in the cross //YS309. In these three cases, an excess of the 0.
glaberrima allele was observed. On the other hand, a deficiency of the 0.
glaberrima allele appeared at the Est-8 locus in the cross //ES70-6. Sano et al. (1979) proposed the "one-locus sporogametophytic interaction" model to account for the sterility of F1 hybrids between the two cultivated species(i.e., parents 0. sativa and 0. glaberrima are respectively assumed to have SaSa and SS; the presence of the S allele in the maternal tissue leads to sterility of gametes Sa). This model explains the distortion observed for Est-2, because marker genes linked to the sterility gene will be subject to distortion. Further, because of the chromosomal location of locus Est-2 and because the 0. glaberrima parent W025 was used by Sano et al. (1979), it is likely that the sterility gene involved in oue experiments is the same as Sa-1 and S-1 designated by Sato et al. (1987).
Table 2.Segregation ratios observed at isozyme loci in four cross
progenies and test of their conformity to Mendelian 1:1 ratio
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Locusa //ES70-6 //SS404 //YS309 //YS45-1
_____________ _____________ _____________ ______________
G S Test(B) G S Test(G) G S Test(B) G S Test(B)
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Cat-1 10 4 ns 17 15 ns 7 2 ns 8 7 ns
Est-1 7 7 ns 11 5 ns
Est-2 12 2 ** 27 5 ***
Est-8 3 11 * 17 16 ns 6 3 ns 8 9 ns
Pgi-1 6 8 ns 20 14 ns 5 4 ns 7 10 ns
Sdh-1 7 7 ns 18 16 ns 9 0 ** 11 6 ns
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a: Symbols follow those proposed in RGN 3, p. 15-17.
G: Plants with the allele from 0. glaberrinia parent, W025.
S: Plants with the allele from 0. sativa parent, ES70-6.
Test(B): Binomial test (Sokal and Rohlf 1981, p. 78).
Test(G): G-test (Sokal and Rohlf 1981, p. 706).
ns: Not significant; * P<0.05; ** P<0.01; *** P<O.OOl.
The "one-locus sporogametophytic interaction" model cannot explain the
observations at the loci Est-8 and Sdh- 1 because opposite results were
observed in different crosses. This means that the genotype of the male 0.
sativa parents has to be considered, in addition of those of W025 and ES70-6.
The differential rates of loss during the cultivation could explain the
deviation at Est-8 in the cross //ES70-6. The hypothesis of an early
differential zygotic selection, involving an albumen-embryo interaction,
seems necessary to account for the distortion of Sdh-1. This was suggested
by Gadish and Zamir (1987) in an interspecific cross between Lycopersicum
esculentum and L. penneli.References
Gadish, I. and D. Zamir, 1987. Differential zygotic abortion in an interspecific Lycopersicon cross. Genome 29: 156-159.
Kochko, A. de, 1987. Isozymic variability of traditional rice (Oryza sativa L.) in Africa. Theor. Appl. Genet. 73: 675-682.
Sano, Y., Y. E. Chu and H. I. Oka, 1979. Genetic studies of speciation in cultivated rice, 1. Genic analysis for the F1 sterility between 0. sativa L. and 0. glaberrima Steud. Jpn. J. Genet. 54: 121-132.
Sato, Y.-I., Y. Sano and M. Nakagahra, 1987. Gene symbols for gametic effect, sterility and weakness. RGN 4: 46-56.
Second, G., 1982. Origin of the genetic diversity of cultivated rice (Oryza ssp.): Study of the polymorphism scored at 40 isozyme loci. Jpn. J. Genet. 57: 25-57.
Sokal, R. R. and F. J. Rohlf, 1981. Biometry (2nd ed.). Freeman, San Francisco. 859 pp.
