Division of Plant Breeding, Genetics and Biochemistry IRRI, P.O. Box 933, 1099 Manila, Philippines

Isozymes are important biochemical markers in genetic and breeding research. The markers have been extensively used to classify rice germplasm into different varietal groups based on pattern of isozyme loci (Pgi-1, Pgi-2, Amp-3, Amp-2 and Amp-l). Germplasm classification on isozyme pattern is useful to breeders for choice of parents in making crosses and to transfer traits between and within groups. We analyzed 6532 rice germplasm lines of Philippines and Thailand. Seeds of these lines were supplied by the International Rice Germplasm Center. Isozyme variability was detected for 16 isozymic loci Cat-1, Pgi-1, Pgi-2, Amp-l, Amp-2, Amp-3, Amp-4, lcd-1, Got-1, Got-3, Adh-l, Sdh-l, Est-I, Est-2, Est-5 and Est-9. These lines were classified into different isozymic groups according to Glaszmann's (1987) classification.

Isozyme analysis revealed that 99% of the germplasm belongs to only two groups I (Indica) and VI (Japonica) in both the countries (Table 1). Contrary to the previous

44 Rice Genetics Newsletter Vol. 13

Table 1. Isozyme classification of Philippines and Thailand rice germplasm

* Figures in parenthesis are percent values.

observations, Philippines rice germplasm has only 36.6% varieties in group I (Indica), while 62.4% belongs to group VI (Japonica). Three varieties were classified into group V which might have been introduced from Indian sub-continent as suggested by their names and 13 were intermediate types which could not be classified in any of the groups and might have been evolved due to either Indica-Japonica hybridization or any spontaneous mutation at one or more isozymic loci used in classification.

Although majority of the rice germplasm from two countries belong to two groups, the distribution of varieties into two groups was entirely different. Unlike Philippines the Thailand rice germplasm showed entirely different varietal distribution. In Thailand 82.7% varieties belong to Group I (Indica) and only 17% varieties were classified in group VI (Japonica). Two varieties fall in group V and 10 were intermediate and could not be classified in any of the 6 groups. It will be interesting to examine possible reasons for such differences in varietal groups of two countries, where conditions for rice culture are more or less similar. (Gene symbol: Old system)

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