1. Evaluation of upland rice genetic resources in northern Laos

1)The United Graduate School of Agricultural Science, Gifu University, Gifu, 501-1193 Japan
2)Faculty of Agriculture, Shizuoka University, Shizuoka, 422-8529 Japan
3)Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, 036-8561 Japan
4)Plant Breeding, Genetics and Biochemistry Division, International Rice Research Institute, DAPO BOX 7777, Metro Manila, Philippines
5)Graduate School of Science and Technology, Chiba University, Matsudo, 271-0092 Japan
6)Graduate School of Life Science, Tohoku University, Sendai, 980-8577 Japan

We investigated upland rice genetic resources in northern Laos, where traditional upland rice cultivars are frequently grown under slash-and-burn field. At present, traditional upland rice cultivars are on the verge of genetic erosion because of replacement by modern improved cultivars, which are promoted to reduce the slash-and-burn upland fields (Sato 1994). Hence, we are in a hurry to collect, evaluate and conserve these genetic resources.

In 1998, we collected 123 upland rice strains from northern Laos: Louang Namtha to Udom Sai (LN sites) and Udom Sai to Louang Prabang (LD sites). To evaluate genetic features of these strains, we examined the nuclear (isozyme) and cytoplasmic (chloroplast DNA) genotypes. The following isozymes: Acp1, Amp2, Cat1, Est2, Pgi1, Pgi2, and Pox2 were used to classify the upland rice strains into indica or japonica types, using the discrimination scores (D score, Ishikawa et al. 1991).

Out of 116 strains, 98 strains (84.5%) were classified as japonica (D score < 0.4), 16 strains (13.8%) were classified as indica (D score > 0.6) and two strains (1.7%) were classified as intermediate type (0.4 < D < 0.6) (Table 1). In addition, we found seven strains having heterozygote isozyme loci. These heterozygotes were not examined because of heterozygosity, hence, were excluded from the calculation of discrimination scores.

The combination of nuclear-cytoplasm genotypes, chloroplast DNA polymorphisms were examined by PCR amplification to determine the presence or absence of a 69bp-deletion at the ORF100 region (Kanno et al. 1993) and classified into deletion type (D type) and non-deletion type (ND type).

Results of isozyme classification and chloroplast DNA types were shown in Fig.1. All 98 strains classified as japonica by isozyme possessed ND type of chloroplast DNA. We considered that typical japonica strains (having japonica genotype in both nuclear and cytoplasm) are predominant in these areas. On the other hand, both D and ND types of chloroplast DNA were observed among the strains having indica isozyme genotype. Twelve strains out of 16 indica strains possessed D type chloroplast DNA, while the remaining four strains have ND

types. It was suggested that these four strains were resultant of natural hybridization between japonica and indica strains, and the direction of geneflow was mainly from indica to japonica because of a relatively low selfing rate of japonica Outcross-pollination has occurred and segregated in slash-and-burn upland fields. Cultivated rice is generally self-pollinated, how- ever about 1 percent cross-pollination could be occurred naturally (Morishima et al. 1992). Hybrids that naturally occurred by cross-pollination between strains could be the source of intermediate strains found in slash-and-burn fields of these areas.

A previous study conducted in these areas did not focused on nuclear-cytoplasm combination (Roder et al. 1996). Here, we presented that such information, which are important to evaluate genetic resources and describe current status of upland rice cultivation.


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