Isozyme variation in traditional rice varieties is very helpful in studying
genetic resource. Preferential interlocus associations of alleles at
independent loci are sources of identification of different gene pools
separated by limited recombination. However, whether the structure observed
dates from before, since or after the domestication remains unsettled. Similar
associations but among tightly linked loci are of less value to study gene pool
separation but may give valuable information on the crop generation processes,
for post demestication recombination has been tempered by linkage.
Loci Est-2 and Amp-3 have been found to be tightly linked in all the various hybrid progenies tested (Sano and Barbier 1985; the author's unpublished data). The recombination values range from 0 to 1.4%. These loci are located on chromosome 3 (numbering system of Shastry et al. 1960).
The bilocus allelic associations found in Asian traditional varieties are given in Table 1-Allelic associations at Est-2 and Amp-3 loci among 2280 Asian varieties. Six groups of a general clasification based on the overall enzymatic variation (Glaszmann 1985) are considered separately. The linkage disequilibrium is extremely stong and a few major allelic combinations are predominant. Some combinations are specific to some of the groups.
Analyzing variation at these two loci in wild rices may be very fruitful. Key questions are: Is such allelic variaiton already existing in the wild rices? Are the same combinations predominant? How are the allelic associations distributed geographically? How are they distributed in the perennial, annual and intermediate populations? Answers can help determine the origin of the linkage disequilibrium observed in the cultivated species and improve our understanding of the process of rice domestication.
Table 1. Allelic associations at Est-2 and Amp-3 loci among 2280 Asian
varieties
=============================================================================
Varietal
Groupsa Est-2 Amp-3 allelesb
(No. of allelesb ====================================
varieties) a c f e d b 0
=============================================================================
1 2 501 - - - - -
Group I 2 675 1 - - - - -
1346 0 143 5 15 - - 4 -
1 - 173 - - - - -
Group II 2 - - - - - - -
173 0 - - - - - - -
1 - - - - - - -
Group III 2 - - - 2 - - -
7 0 - - - 5 - - -
1 - - - - - - -
Group IV 2 - - - - - - -
11 0 - - - 11 - - -
1 - - - - - - -
Group VI 2 - - - - - - -
504 0 364 13 - - - - -
Intermediates 1 1 63 - - 1 - -
110 2 10 - - - - - -
0 0 4 - - 11 - 11
Total
1 3 864 - - 1 - - 868
Total 2 685 1 - 2 - 4 - 692
2280 0 517 22 15 16 67 - 83 720
total 1205 887 15 18 68 4 83 2280
=============================================================================
a: See Galszmann, 1985B: Accessions carrying the various alleles in collections maintained at the International Rice Germplasm Center, IRRI, Lost Banos, Philippines (Acc. No.) and the National Institute of Genetics, Mishima, Japan (NIG):
Est-2 Amp-3
===== =====
1: Surjamkuhi (Acc. 8256; NIG 451) a: Pei-Ku (Acc. 8236; NIG 108)
2: Pei-ku (Acc. 8236; NIG 108) c: Surjamkuhi (Acc. 8256; NIG 451)
0: Taichung 65 (Acc. 79; NIG 504) f: Carreon (Acc. 32575); Wan-li-sen
(NIG 1075)
e: Aswina (Acc. 26289)
d: Meedon hmwe (Acc. 33377)
b: Leuang Pratew (Acc. 27762)
O: Basmati 370 (Acc. 6426); Paddy type
24 (NIG 444)
Glaszmann, J.C. 1985. A new insight into Asian cultivated rice classification from isozyme studies. RGN 2: 48-51.
Sano, R. and P. Barbier, 1985. Analysis of five isozyme genes and chromosomal location of Amp-1. RGN 2: 60-62.
Shastry, S.V.S., D.R.R. Rao and R.N. Misra, 1960. Pachytene analysis in Oryza. I. Chromosome morphology in Oryza sativa. Indian J. Genet. Plant Breed. 20: 15- 21.