12. Set-up of a permanent observation site of wild rice in Thailand 

Yo-Ichiro sato' , Songkran chitrakon^2 , Prayote charoendham^3 , Yoshiya SHIMAMOTO'^4 and Hiroko morishima^5

1) Faculty of Agriculture, Shizuoka University, Shizuoka, 422, Japan

2) Pathum Thani Rice Research Center, Pathum Thani, Thailand

3) Prachinburi Rice Research Center, Prachinburi, 25150, Thailand

4) Faculty of Agriculture, Hokkaido University, Sapporo, 060, Japan

5) National Institute of Genetics, Mishima, 411, Japan

 A permanent observation site was set up in a huge natural population of wild rice ( Oryza rufipogon) in Prachinburi prefecture of Thailand in the winter of 1993. The population covers the area of ca.250m x 200m, and is adjacent to an experimental field of Prachinburi Rice Research Center. Plant cover of wild rice is almost 100 percent at the center of the population.

We have been trying to establish several permanent sites of wild rice in this country, hoping to get a long-term sequential data on the life history of wild rice plants and the change of their genetic population structure. Yet, previous attempts have not been successively performed, because almost all natural populations we were monitoring disappeared due to a drastic change of habitat environments (Morishima et al. 1984; Sato 1994). As the establishment of this site has been approved as a Royal Project of Thailand, this population may be assured of enjoying its longevity.

We set up two subsites in this population, whose size is one hectare (100m x 100m) each. Surrounding one subsite, a fence was constructed to protect from invasion of catties (without disturbance, ND-site). Another site has no barrier so as to let them enter freely (with disturbance, D-site) (Fig. 1). We intend to continue observation and sampling for demographic and genetic studies until 2000. Preliminary results of the observations up to now are as follows.

1) Plants of the population produce many panicles every year. Average number of panicles per square meter exceeded 100. No significant difference was observed in number of panicles per unit area between ND- and D-sites.

2) Number of soil-buried seeds per square meter was from several ten to 100, though it varied from spot to spot. Thus the plants have a capacity of sexual reproduction.

3) In rainy season, water came up to 200 to 250cm deep on the average. Wild-rice plants of this site show floating ability.

4) Vegetative organs developed in the previous season died in dry season. However, tremendous number of new shoots came up from nodes of the stems of the previous

66 Rice Genetics Newsletter Vol. 13


 
 

Fig. 1. Permanent observation site of wild rice in Prachinburi, Thailand. A: ND- site (March, 1994), B: D- site (May, 1995).  
season

5) In the newly developed shoots in the beginning of rainy season, proportion of ratoons rising up from old stems were predominant. Plants from buried seeds seemed 5 percent or less.

6) No panicles having features of cultivated rice were observed, suggesting that gene flow from cultivated rice is rare, if any.
Research Notes 67
Judging from these observations, plants of this population have a perennial-annual intermediate or intermediate-perennial habit. Monitoring the change of genetic constitution based on DNA and isozyme variation will be carried out. Differences between ND-and D-sites will be also investigated.

Natural populations of wild rice has become mostly extinct during the last two decades in the tropical Asia (Chitrakon 1994). The in situ preservation of genetic resources of rice is expected to prevent genetic erosion. Scientists who are interested in the study and plant materials of this population, please contact anyone of the present authors.

References

Chitrakon, S., 1994. Genetic erosion in Thailand, In : (Sato ed.). Ecological-genetic studies on wild and

cultivated rice in Tropical Asia (4th survey). TROPICS 3: 223-226.

Morishima, H., Y. Shimamoto, Y. Sano and Y.I. Sato., 1984. Observations on wild and cultivated rices in Thailand for ecological-genetic study. Report of study-tour in 1983. Rep. from Nat. Inst. Genet., Japan.

Sato, Y.I., (ed.) 1994. Ecological-Genetic studies on wild and cultivated rice in Tropical Asia (4th survey). TROPICS 3:189-246.