8. Genetic divergence among rices from Northeast India

Institute de Recherches Agronomiques Tropicales et des Cultures Vivrieres (IRAT), CIRAD, B.P. 5035, 34032 Mont ellier Cedex, France

Various authors (Vairavan et al. 1973; Seetharaman et al. 1974; Srivastava 1978; Asthana and Majumber 1981; Sasikumar and Sardana 1987) have shown a wide morphological variability of the rices from Northeast India (Assam Rice Collection). Character combinations intermediate between Indica and Japonica have been observed.

We have used variation of 289 cultivars from various parts of Northeast India at 14 isozyme loci to quantify genic diversity and to study the distribution of the varieties into the varietal groups (I to VI) defined by J.C. Glaszmann (1987) among Asian native rices.

The zymograms were obtained at IRRI and the statistical analysis was performed at IRAT.

The gene diversity index (Nei 1975) was 0.341 for Northeast Indian rices. It is close to that calculated for all Asian rices (0.346), and thus very high considering the small size of the area under survey.

The distribution into the enzymatic groups for each region is shown in Table 1 and compared with the distribution for the whole of Asia. All the enzymatic groups are encountered, except groups III and IV, which are very small at the Asian scale and restricted to deepwater areas in Bangladesh. Group I (typical Indica) is majority (59.9%) but groups VI (typical Japonica) as well as groups II and V are also found in significant frequencies (8.7%, 18.3% and 7.6%, respectively). The varieties of group VI are mostly located in the mountainous areas (Meghalaya and Arunachal Pradesh). Varieties which cannot be classified in any of the groups were ontly 5.5%, which is not significantly higher than their global frequency in Asia (5.3%). As far as isozymes are concerned, the varietal

We then performed a discriminant factor analysis (DFA) on the 273 varieties of groups I, II, V and VI using 13 morphological characters from IRGC database to identify the characters which best differentiate the four enzymatic groups (Table 2).

Duration (MAT) was the most discriminating character; it enabled to assign 47% of the varieties to their respective groups. MAT, GRL (grain length) and GRW (grain width) all together enabled to classify 70% of the varieties. Groups i, II and V, generally classified as the Indica type based on morphology, were significantly different from each other for duration. The varieties of group VI were differentiated from the other varieties by the characters which usually differentiate Japonica from Indica: wide grains, wide leaves and low tillering.

The high level of morphological diversity often observed in Northeast India is to be related to a very high genic diversity and the coexistence of most known varietal types as identified with isozymes. However, such a diversity displays an ordinary organization and there does not seem to exist more atypical forms than in Asia as a whole. Furthermore, the relation between the enzymatic classification, and parameters such as altitude of origin and growth duration suggests that ecological specialization has already taken place.

Asthana, A. N. and N. D. Majumber, 1981. Studies in rice germ plasm of North Eastern hill region. Research Bull. n11, ICAR, India.

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

Sasikumar, B. and S. Sardana, 1987. Evaluation of rice germplasm in Tripura. Plant Genet. Res. Newsl. 71: 31-33.

Seetharaman, R., D. P. Srivastava and D. P. Ghorai, 1974. Preliminary studies in rice cultivars from North East India. Ind. J. Genet. & Plant Breed. 34(2): 143-149.

Srivastava, D. P., 1978. Diversity in the late duration rice cultivars from North East India. Oryza 15(1): 26-33.

Vairaran, S., E. A. Siddig, V. Arunachalam and M. S. Swaminathan, 1973. A study on the nature of genetic divergence in rice from Assam and North East Himalayas. Theor. Appl. Genet. 43: 213-221.