1. Biogeco; INRA; Univ. Bordeaux; F-33610 Cestas France
2. Dynafor; INPT; EI Purpan; INRA; Univ. Toulouse; F-31320 Auzeville France
3. SAVE; Bordeaux Sciences Agro; INRA; F-33140 Villenave d'Ornon France
4. School of Biological Sciences; Royal Holloway University of London; Egham Surrey TW20 0EX UK