1. Plant Environment Lab.; Univ. of Reading; Cutbush Lane, Shinfield Reading RG2 9AF UK
2. Crop and Environmental Sciences Division; International Rice Research Institute; DAPO Box 7777 Metro Manila Philippines
3. CIMMYT, Km. 45, Carretera Mexico-Veracruz, El Batan; Texcoco Edo. de México, CP 56130 México
4. Dep. of Plant and Soil Science; Univ. of Aberdeen; Aberdeen AB24 3UU UK