Acknowledgements
This study was conducted with financial support from the
Special Initiative Fund of the International Rice Research
Institute, Philippines, and from the program of S-2 (3) b.by
the Global Environment Research Fund of the Ministry of the
Environment, Japan. We thank Mr. Banthasack Vongphouthone
and Mr. Visone Navongxay for their field assistance, Dr. Kazuki
Saito for his advice and Dr. Keisuke Katsura for reviewing this
paper.