11. Peculiar genetic characteristics of O. rufipogon from Western India

ORSTOM/CEPE, CNRS BP 5051. 34033 Montpellier Cedes, France. Present address: 1) Universite d'Abidjan, BP322 Abidjan 04, Cote d'Ivoire; 2) Department of Plant Breeding, 252 Emerson Hall, Cornell University, Ithaca, NY 14853-1902, USA

In October 1985, A. Ghesquiere and G. Second visited Western India for collection of wild and cultivated rices. The collection was analyzed by isozyme electrophoresis according to the method of Second (1985). Various quantitative measurements related to the annual-perennaial life-form differentiation in this group were characterized according to Morishima and Oka (1961). The collection of O. rufipogon studied included: five accessions of a typical annual form collected in the arid environment of Gujarat, two perennial forms and a weedy form from the more humid environment of Goa area and 21 accessions of an intermediate annual-perennial form in the area from Gujarat to Goa. Local cultivars of O. sativa, which matured simultaneously with O. rufipogon in the same area, were also studied. They included six ordinary cultivars and two land races from Gujarat. The latter two were considered "primitive" because of long awns and shattering habit, although they were cultivated and their maturity was uniform.

Thirty-six presumed isozyme loci were surveyed, of which 22 were polymorphic in the present material. The data for the 22 loci which were studied by Second (1985) could be used for comparison of isozyme variation between the materials from Western India and from other parts of Asia, i.e., Acp-1, Adh-1, Amp-1, Cat-1, Est-2, Est-9, Got-1, Got-3, Mdh-1, Pgd-1, Pgd-2, Pgi-1, Pgi-2, Pox-1, and 8 other presumed loci (Gdh-A, Gdh-B, Gp-A, Idh-A, Mdh-B, Mdh-C, Pgm-A, and To-A).

A dendrogram (Fig. 1) was constructed based on Nei's (1972) standard genetic distances between the six strain-groups mentioned above, into which the present material was classified. The result of a principal component analysis of the combined data of the present study and those of Second (1985) is shown in Fig. 2. The following four points can be raised form the results in Figs. 1 and 2.

1) Among the various forms of wild rice comprising the Sativa group of the genus Oryza, O. breviligulata from Africa resembled O. rufipogon from Western India closely at the isozyme level. In fact, the accessions collected in Gujarat were identical at any of the 36 loci studied with many accessions of O. breviligulata and its cultivated form, O. glaberrima, although at Pgi-1 they had allele 2 which was less frequent in the African species than allele 3.

2) The wild rices collected in the area of Goa and in-between Gujarat and Goa showed electrophoretic characteristics of either O. breviligulata or O. rufipogon from other parts of India.

3) In the area of Goa, where both the annual and perennial forms were found, the two forms were quite similar at the isozyme level. The isozyme diversity among wild rices of Western India did not reflect the differetiation of life forms although they reflected a geographical cline extending from Gujarat to Goa, which may be from an arid to a more humid environment.

4) The primitive cultivars closely resembled the wild rice of Fujarat in isozymes, although they differed form the latter in alleles at two loci, Acp-1 and "Arap-A". Other local cultivars showed no such resemblace with the wild rice in the same area. Details of these observations were reported by Lolo (1987).

Crossing experiment were performed between strains of West Indian O. rufipogon and O. breviligulata. A cross between a rufipogon strain from Gujarat and a breviligulata strain from Chad showed partial F\1\ fertility, although complete sterility has been usually reported between these two taxa.

The material was also observed at the level of total chloroplast DNA RFLPs (Dally 1988) and nuclear ribosomal external spacer length by Florence Cordesse (pers. comm.). At both levels. O. rufipogon strains and primitive cultivars from Western India showed close similarities with subspecies japonica of O. sativa, in contradiction with the results at the isozyme level.

From these observations, we propose that O. rufipogon in Western India represents an original genetic group that should require particular attention in its evaluation as genetic resources and in the study of evolution of rice. It could also represent a genetic bridge between O. sativa and O. glaberrima.

Based on these data, we also propose a hypothesis of introduction of African germplasms (O. breviligulata or O. glaberrima) into Western India through the intervention of man, possibly by a similar route as that for sorghum and pearl millet. The introduction would have been followed by introgression from O. rufipogon and O. sativa.

Fig. 1 A dendrogram (UPGMA) based on Nei's genetic distances between six groups of strains collected from western India: Weedy (We), perennial (Pe), annual-intermediate (Ai), annual (An), "primitive cultivar" (Cp), and ordinary cultivar (Cu).

Fig. 2. Various strain groups of O, rufipogon, O. breviligulata, O. sativa, and O. glaberrima scattered according to the first and second vectors obtained from principal component analysis of isozyme data for 22 loci. Strains from western India are encircled and are designated by the same symbols as used in Fig. 1. Other symbols are: JAP-subspecies japonica, IND-subspecies indica, GLA-O. glaberrima, BV-O. breviligulata, CX-O. rufipogon from China, other symbols for O. rufipogon: IW (weedy), IP (wild perennial), IA (wild annual), and II (wild intermediate) from South Asia (India); TW (weedy), TP (wild perennial), TA (wild annual), and TI (wild intermediate) from continental Southeast Asia (Thailand); SW (weedy) and SP (wild perennial) from insular Southeast Asia.

References

Dally, A., 1988. Analyse cladistique de mutations de l'ADN chloroplastique et phylogenie des riz (section Euoryza du genre Oryza). Coll. Etudes et These, ORSTOM, Paris, 115 pp.

Ghesquiere, A. and G. Second, 1985. Collection and observations of wild rice (Oryza). A report of survey from October 1 to 28, 1984. 41pp mimeogr.

Lolo, O.M., 1987. Analyse comparee de la structure genetique d'Oryza rufipogon Griff. en Inde de l'Ouset: Un exemple d'introduction suivie d'introgression genetique en Inde d'un riq d'origine africaine. These 3eme cycle. Univ. Paris XI. 107pp+19annexes.

Morishima, H., H.I. Oka and W.T. Chang, 1961. Directions of differentiation in populartions of wird rice, Oryza perennis and O. sativa f. spontanea. Evolution 15: 326-339.

Nei, M., 1972. Genetic distance between populations. Am. Nat. 106: 283-292.

Second, G., 1985. Evolutionary relationships in the Sativa group of Oryza based on isozyme data. Genet. Sel. Evol. 17(1):89-114.