25. Isozyme polymorphism and classification of rice varieties from Burkina Faso in Africa

Moussa SIE1 and A. GHESQUIERE2

1) INERA, BP 540, Bobo Dioulasso, Burkina Faso

2) ORSTOM, LRGAPT, BP 5045, 34032 Montpellier cedex 1, France

In Burkina Faso, rice landraces are well represented and give a typical feature of the rice growing in the Sahelian area of Africa. In order to carry on genetic evaluation of traditional rice cultivars, 283 strains of O. sativa collected in all over Burkina Faso were analysed for their isozyme polymorphism. The 15 loci currently utilized to classify rice varieties were taken (Glaszmann 1987) with 4 aditionnal loci: Acp-2, Pox-3, Pgd-1 and Enp-1. All of the common alleles seen in Asia were present, most of the varieties were Indica (Group I defined by Glaszmann 1987) and corresponded to lowland varieties; 13 varieties fell in group VI and had been cllected in the area close to Ivory Coast where rainfall is sufficient to grow upland rice; the two last varieties displayed the allele Pgi-23 and the characteristic pattern of group II for the other loci. Specific alleles of groups III, IV and V were not observed and confirmed that representatives of minor groups are absent or at very low frequencies in Africa and in Madagascar (Rabary et al. 1989). An allele Enp-12 slightly faster than Enp-11 was found in one accession and an allele denoted Pgd-10 with a significantly reduced activity was also observed. Identification of isozyme patterns on the four loci, Pgi-1, Pgi-2, Cat-1 and Est-2 permitted previously evolutionary inferences on the origin of Indica and Japonica types in assuming that presumed "hybrid" patterns could be obtained by various combinations of "parental" types (Second 1982). This classification in "parental" and "hybrid" types was extended and compared with the classification in 6 groups established by Glaszmann (1987) to obtain additional informations about African rices in respect of Indica-Japonica differentiation (Table 1). The two classifications were quite consistent for the two major groups and only a single "intermediate" pattern could be shared by these groups: this pattern is associated with a positive phenol reaction for Indica varieties and with a negative reaction for Japonica varieties. In minor groups, this "intermediate" pattern corresponded also to a possible genotype aside patterns defined by rare alleles at Pgi-2 locus. A characteristic of Indica varieties from Burkina Faso was that "hybrid" patterns were more frequent than "parental" association which is usually found in Asia, this over representation of "hybrid" patterns concerned also the Japonica counterpart of African rice varieties (Kochko 1987).

The analysis of Indica-Japonica classification was refined in taking discriminant scores. A more convenient formula, D\ind\=(F\ind\-F\jap\)/F\sat\, was chosen to 

Table 1. Distribution of 286 accessions of rice varieties from Burkina Faso
according to: 1) the classification in 6 isozyme groups defined on 15 loci
(Glaszmann 1987) 2) the patterns observed on 4 loci: Pgi-1, Pgi-2, Cat-1,
Est-2.  Patterns not concerned by the allele composition of the different
isozyme groups are noted by (-)
===============================================================================
                 multiallele associations Distrib. of access. in isozyme groups
                 ======================== =====================================
Type of patterns Pgi-1 Pgi-2 Cat-1 Est-2    I   II   III  IV   V    VI
                                          (Indica)               (Japonica)
==============================================================================
"parental" Japonica  2     1     2     0    -    -     -   -   0     0
"hybrid" Japonica    2     1     2     1    -    -     -   -   -     2
"hybrid" Japonica    2     1     1     0    0    -     -   -   0     9
intermediate         2     1     1    1-2  49    0     -   0   -     2
"hybrid" Indica      1     1     1    1-2  175   -     -   -   -     -
"parental" Indica    1     2     1    1-2   23   -     -   -   -     -
miscellaneous Indica(1) 1-2 1-2  1    0-1   21   -     -   -   -     -
particular patterns (2) 2  3-4   1     1     -  2(a) 0(a) 0(b) 0(b)  -
       Total                               268   2                  13
==============================================================================
(1) other "hybrid" indica patterns involving frequent alleles in the two
associations: 1110 and 2211.  (2) patterns involving rare alleles on Pgi-2
loci: (a): Pgi-23, (b): Pgi-24.
enlarge the distribution and highlight the intermediate values. To obtain score values independent of our sample, we took the allele frequencies reported by Glaszmann (1987) in groups I and VI and in O. sativa as estimations of F\ind\, F\jap\ and F\sat\ respectively. Score values were attributed for each frequent allele (F\sat\ > 0.05) at each locus and a mean index value on the fifteen loci was computed to represent the likeness to the Indica type in isozymes. In group I, this mean index could range theoretically from -0.13 to 0.92 but no negative values were found. The varieties having the "parental" Indica pattern showed the highest scores when compared to the "hybrid" and "intermediate" clusters which displayed consequently a larger genetic diversity (Table 2). Moreover, these two last groups could be also characterized by increased frequencies for null alleles (Est-50, Est-10 and Enp-10). Particularly, whereas Enp-10 was not found in "parental" group and was reported as quasi absent in Asia, the frequency of this allele could reach 0.5 in our "hybrid" group. An analysis of correspondences performed with the 268 strains of group I on 15 polymorphic loci displayed two clear-cut groups based on the presence or absence of Enp-11 (data not shown). These results indicate that Indica- Japonic differentiation is blurred in Africa even if it remains the major component in the genetic organisation of rice varieties. A similar trend is observed in Madagascar where varieties look more intermediate along the Indica-Japonica continuum (Rabary et al., 1989) and this suggests that genetic differentiation of rice in Africa can take original ways following local selection by farmers and 

Table 2. Distribution of isozyme patterns found in varieties of Group I
following a mean D score calculated on 15 loci and discriminating between
Indica and Japonica types
===============================================================================
                                   D  values
Types of pattern      =============================================     H
                      0-0.25  0.25-0.50   0.50-0.75  0.75-1         (19 loci)
===============================================================================
intermediate            0.10       0.80        0.10                  0.22
miscellaneous indica               0.86        0.14                  0.16
"hybrid" indica                    0.08        0.62    0.32          0.19
parental" indica                               0.35    0.65          0.10

  Total Group I         0.02       0.27        0.47    0.40          0.24
==============================================================================
intersubspecific hybridization between Indica and Japonica varieties.

References

Glaszmann, J. C., 1987. Isozymes and clasification of rice varieties. Theor Appl Genet 74: 21-30.

Kochko, A. de, 1987. Isozyme variability of traditional rice Oryza sativa (L.) in Africa. Theor Appl Genet 73: 675-682.

Second, G., 1982. Origin of the genic diversity of cultivated rice (Oryza spp): study of the polymorphism at 40 isozyme loci. Jpn. J. Genet. 57: 25-57.

Rabary, E., Noyer, J. L., Benayer, P., M. Arnaud and J. C. Glaszmann, 1989. Variabilite genetique du riz (Oryza sativa L.)a Madagascar. Origine de types nouveaux. L'Agronomie Tropicale 44: 305-312.