1. a International Rice Research Institute , P. O. Box 933, Manila , 1099 , Philippines
2. b Institute of Tropical Agriculture , University of Leipzig , Fichtestr. 28, Leipzig , 04275 , Germany
3. c Department of Plant and Soil Science , Montana State University , Bozeman , MT , 59717–0312 , USA
4. d Department of Agricultural Chemistry , Kangweon National University , Chuncheon , 200–701 , Korea