A wild rice (BKK) strain showing sterile spikelet and big leaves inhabited at the basin of the Chao Phraya river of Bangkok city, Thailand. The BKK strain was found as a natural triploid and thus its origin has been interested long time. Three different-sized fragments were amplified in RNA polymerase I largest subunit ( PolA1 ) gene, which is a single-copy nuclear gene per haploid genome. Short type (0.14 kb) intron 20 sequence of BKK strain was identical to that of O. rufipogon and O. sativa . Phylogenetic analysis showed that long type (1.5 kb and 1.8 kb) intron 20 sequences of BKK strain were closely related to that of O. longistaminata and O. officinalis , respectively. We analyzed protein tag (Ptag) sequence encoded by exons 19 to 21 of PolA1 gene. Determined three Ptag sequences of BKK strain were identical to that of O. rufipogon , O. longistaminata , and O. officinalis , respectively. Relative DNA content of nuclei in O. officinalis and BKK strain was 1.5 and 1.75 times than that in O. sativa , respectively. And BKK strain contained CentO-C1 repeats, which were unique to O. officinalis . These results indicated that BKK strain comprised three genomes of O. rufipogon , O. longistaminata , and O. officinalis .
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