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11. Relationships between wild, weedy and cultivated rice in Malaysia

Duncan A. Vaughan¹, Abdullah Md. Zain ²H. Watanabe ²and K. Okuno¹

1) NIAR, 2-1-2 Kannondai, Tsukuba 305, Japan
2) Rice Research Center, MARDI, Seberang Perai, Malaysia
3) JIRCAS, Tsukuba 305, Japan     In 1988 weedy rice was reported from Tanjung Karang irrigation scheme on the west coast of West Malaysia. Subsequently, it was reported in the MUDA irrigation scheme which is the main rice production area in Malaysia. It was not apparent why the weedy rice had suddenly emerged. Samples of the wild rice Oryza rufipogon (7 samples), weedy rice (28 samples) and cultivated rice (9 samples) from the MUDA area, as well as MARDI genebank accessions of varieties that had been commonly grown in West Malaysia over the past 15 years, were included in our analysis,
    We undertook RAPD (randomly amplified polymorphic DNA) analysis using standard protocol (Williams et al. 1993). A total of 13 primers were selected which showed inter-sample variation and 23 polymorphic bands were scored (presence or absence) and data used for cluster analysis. Wards coefficient of similarity was measured (Ward 1963). The results are shown in Fig. 1. The analysis indicates that 0. rufipogon, which is common in MUDA is distinct from the weedy rice and cultivated rice. Weedy rice fell into the same cluster as cultivated rice and this suggests that weedy rice evolved from the cultigen. One population of 0. rufipogon was in the same cluster as weedy and cultivated rice. This population, from near Aloe Setar, is photoperiod insensitive, and may have introgressed genes from cultivated rice.
    Features of Malaysian rice culture which may have favored the evolution and spread of weedy rice include:
1. The practice of allowing dropped seeds to grow and produce a crop in the subsequent season. Use of dropped seeds to establish a crop was prevalent in the 1980's during the off (dry) season when irrigation water is limited in some areas;
2. The use of easy shattering varieties;
3. The use of combine harvesters which move from one rice growing area to another. Wards coefficient of discrimination

References

Ward, J., H. 1963. Hierarchical grouping to optimize an objective function. J. A. S, A. 58: 236-244.
Williams, J. G. K., M. K. Hanafey, J. A. Rafalski and S. V. Tingey, 1993. Genetic analysis using randomly
amplified polymorphic DNA markers. Methods in Enzymology 218: 704-740.