[1] Natl Inst Agr Bot, Cambridge CB3 0LE, England
[2] John Innes Ctr, Norwich Res Pk, Norwich NR4 7UH, Norfolk, England
[3] Colorado State Univ, Ft Collins, CO 80523 USA
[4] Int Rice Res Inst, Plant Breeding Genet & Biotechnol Div, Manila, Philippines