1. Dep. of Agronomy and Range Science Univ. of California Davis CA 95616 USA
2. Land, Air and Water Resources Univ. of California Davis CA 95616 USA
3. Int. Rice Research Inst., Lao‐IRRI Project Vientiane Laos
4. Dep. of Agronomy Purdue Univ. West Lafayette IN 47907‐1150 USA