2. Indica-Japonica differentiation of Bangladesh rice cultivars detected by isozyme analysis
H.W. CAI and H. MORISIMA
National Institute of Genetics. Mishima, 411 Japan
Bangladesh rice cultivars are known to include some unique isozyme genotypes which are not found in cultivars of other regions (Glaszmann 1987). To elucidate genetic diversity in Bangladesh rice cultivars, a total of 144 land races were analyzed for their isozyme variation. These land races are classified into Aman, Aus and Boro based on their cropping season. Two typical Indica and two typical Japonica cultivars were also used as checks. The isozyme variation was assayed as described by Cai (1995).
The following 21 isozyme loci were assayed; Sdh1, Pgd1, Pgd2, Am1, Amp2, Amp3, Est1, E2t2, Est3, Ext5, Est9, Est10, Est11, Est12, Est13, Mal1, Mal2, Acp1, Acp2, Acp4 and Pox2. These loci were polymorphic except Pgd1. Average genie diversity estimated in these materials was 0.38. Of the 144 cultivars examined, 120 different genotypes based on isozyme alleles were found. The most frequent genotype consisted of 4 cultivars, and most genotypes were represented by only one cultivar. The genotype diversity shown by H'=-Σpi lnpi (pi stands for the relative proportion of ith genotype) was 5.6 which is the highest among the values obtained for other regions so far studied (Sano and Morishima 1992).
In the scatter diagram obtained from factor analysis based on isozyme data, cultivars examined were classified into four groups as shown in Fig. 1. Judging from ecotype designation of these cultivars used in Bangladesh and from our own observation in the experimental field in Japan, constitution of each group was inferred as follows. Group 1 (81 cultivars) includes majority of the transplanted Aman (T. Aman) cultivars and a few of Boro and Aus cultivars. Group 2 (26 cultivars) consists of Aman cultivars grown in deepwater area (Broadcast Aman). Group 3 (24 cultivars) includes mostly Aus varieties. Group 4 (17 cultivars) consists of T. Aman cultivars, primarily with small grains.
The major varietal group in Bangladesh (group 1) was found to belong in Indica type (similar to indica cheks). In addition, it was found that group 2 cultivars (deepwater rices) are Japonica-like and closer to Japonica checks. Group 3 is represented by Aus cultivars which are differentiated from but closer to typical Indicas (group 1). Group 4 seems to be a minor group. Interestingly, deepwater rices were found to carry a special isozyme allele Est10-4 which is frequently found in Asian common wild rice 0. rufipogon but is rare in other cultivars (Cai and Wang 1994). This finding suggests Bangladesh deepwater rice have inherited this allele from its wild progenitor.
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