Fusarium oxysporum Schl. var. vanillae (Tucker) Gondon is known to cause root rot in Vanilla planifolia Andrews in most regions where it is grown, including the major plantations in Xishuangbanna, Yunnan Province of China. This is of serious economic concern to the Province since the vanilla flavouring extractable from the beans of the plant is a valuable food product and an important export commodity. There are no fungicides registered for the control of Fusarium root rot and the only available chemical control methods are ineffective and cause serious contamination of the soil. Breeding for resistance is difficult when no dominant gene is known or where little information is available on fungal pathogenicity. Biocontrol is the main alternative for disease control in this crop, an attractive approach because of increasing concerns for environmental protection. The investigation considers two biocontrol strategies: first the introduction of virulent, antagonistic, non-pathogenic strains, closely-related to the pathogen, to overcome pathogenic populations in infected soils; second the use of essential oils with antimicrobial properties when applied to infected soils. Pathogenicity tests have been done on 81 out of 87 F. oxysporum isolates collected in Yunnan Province. Among these, 32 isolates were non-pathogenic and 49 were pathogenic. The pathogenicity results showed the complexity of F. oxysporum in Yunnan. Seventeen isolates were recovered from the Daluo plantation, of which 14 were pathogenic isolates and 3 non-pathogenic isolates; 26 from the Menglun plantation, in which 12 were pathogenic and 14 were non-pathogenic; 18 isolates from the Manjingdai plantation, in which 12 isolates were pathogenic, whilst the other 6 were non-pathogenic and 20 were obtained from the plantation in Hekou i County, of which 11 were pathogenic isolates and 9 were non-pathogenic. Genetic diversity within this population of F. oxysporum has been investigated with respect to vegetative compatibility and to determine the relationship between VCGs and virulence. The VCG results showed that the 87 strains of Fusarium oxysporum f.sp vanillae isolated from Yunnan Province were complex. They could be distributed into 12 different VCGs and that a direct relationship between VCGs group and virulence could not be drawn. Two non-pathogenic strains, ML-5-2 and HK-5b-4-1, have been screened from 87 strains as candidate biocontrol agents by pathogenicity and VCG, which are self-incompatible and closely related to the pathogens. These two strains were effective in vanilla root rot control in controlled environments, but their effects in field experiments were less conclusive. Seven essential oils, which have long been regarded as having inhibitory effects on pathogens in nature, have also been investigated as biocontrol agents. Three oils, cinnamon oil, thyme oil and clove oil, were effective in inhibiting the growth of pathogen in vitro. These oils may develop into useful components of different management strategies with non-pathogenic strains. For the future, consideration will need to be given to the mechanism(s) of the interaction of the antagonistic components with the soil microbe population and host plant and also to appropriate formulation, to take account of soil type, crop status, cultural practices, environmental and economic factors. Biocontrol methods have considerable potential but must be acceptable to farmers as part of an overall crop management programme.

La vanille, utilisée en alimentation et parfumerie, est une orchidée originaire d’Amérique centrale et maintenant cultivée dans l’océan indien (Vanilla planifolia, 97% de la production mondiale) et dans l’océan pacifique (Vanilla tahitensis, 3% de la production mondiale, essentiellement en Polynésie française).J’ai montré que Vanilla tahitensis était aussi sensible que Vanilla planifolia à la fusariose et représentait la maladie principale de la vanille en Polynésie française comme dans le reste des zones de production des vanilles aromatiques. J’ai participé à démontrer qu’il s’agissait d’une nouvelle espèce de Fusarium oxysporum « f. sp. radicis-vanillae » car elle ne s’attaque qu’au cortex racinaire et ne pénètre que peu dans les tissus vasculaires. J’ai suivi pendant 4 ans l’évolution qualitative et quantitative des dégâts dus à 6 pathogènes et ravageurs dans 51 plantations à Raiatea, principalement des ombrières. J’ai ainsi montré que, contrairement aux autres pathologies et ravageurs, la fusariose connaissait un développement presqu’exponentiel ces 3 dernières années, comme c’est également le cas sur Vanilla planifolia dans le reste du monde. Ayant, par ailleurs, conduit un travail d’enquête auprès des producteurs, j’ai indiqué (l’analyse statistique et la modélisation afférente ne sont pas terminées) que le soin apporté aux lianes par les producteurs était essentiel au bon contrôle de la fusariose. / Vanilla species, used for aroma and flagrances, are orchidaceae originated from central America. They are now mostly cultivated in the Indian ocean (Vanilla planifolia, 97%, mainly in Madagascar, Indonesia, India and smaller islands from the Indian ocean) and in the Pacific ocean (Vanilla tahitensis, 3%, mainly French Polynesia).I have shown that Vanilla tahitensis was as susceptible as Vanilla planifolia towards fusarium root rot. It does represent the major losses on Vanilla tahitensis in Raiatea like reported for all the other areas of vanilla production worldly. I have participated to show that this fungus was delimited to root cortex maceration and did not invade vascular tissues, reason for which we use a new name for this pathogen : Fusarium oxysporum f sp radicis-vanillae.I have followed the etiological and epidemiological characteristics of this disease and of 5 other pathogens and insects on 51 Vanilla plantations, mainly shade-houses, during 4 years, for each vine in cohort analysis manner. I have shown, among this 6 biological causes of loss, fusarium root rot was the only one to present an exponential trajectory within the last 3 years, while the other causes remain stable or display a year increase because of climatic reasons. I did interview all the producers owning these plantations and analyze statistically the answers to the very numerous questions. The statistical and modelling analysis is not yet finished. Nevertheless, I can already claim that regular vine cleaning is absolutely necessary to maintain the vanilla plantations healthy, something which, unfortunately is not a rule for everyone.