A strategy towards bioprotection of tropical crops: Experiences and perspectives

Tropical crop infestation by soil borne parasites (pineapple : Rotylenchulus reniformis and banana : Pratylenchus coffea e ) cann ot be controlled anymore by pes ticides in French Antillas under the new European regulations . Therefore, we investigated the possible contribution of induced systemic resistances ( ISR ) to biocontrol pests and to develop more environmentally friendly agrosystems. In Martinique ( Campus Agro - environnemental Caraïbe ), we are presently testing a strategy based on current knowledge on ISR through interaction between plants and beneficial microorganisms. The investigations are based on four main hypotheses: 1) The inoculum of soil borne parasites can be reduced introducing non - host rotation plants. Cover crops were selected on the basis of several functional traits (non - host status, high biomass), for their contribution to a balanced microfauna in the rhizos phere, and for their positive effect on soil mycorhization potential. 2) The selection of pineapple and banana varieties able to develop ISR AND adapt their metabolism to environmental changes is essential. We found differential responses against nematodes to an ISR inducer (methyljasmonate, 10 - 4 M) in several pineapple and banana varieties and we are now searching for a relation with markers of plant adaptability to environmental changes (genes for cysteine - proteases and their inhibitors phyto - cystatins). 3 ) The successful development of ISR responses is dependent on the capacity of a plant to tolerate abiotic stresses (drought, temperature, salinity...) in addition to the pathogens. As ISR may also be part of the global adaptability of plant metabolism to tol erate abiotic stresses from their habitat, we investigate the possible links between stress level and a plant's capacity to induce efficient ISR against soil - borne parasites ( ongoing ). 4) Pineapple and banana root systems bear diazotrophic bacteria (endoph ytic) that can be used as ISR inducers in the field. Seventy - five and ninety - one diazotrophic bacteria strains (endophytic) respectively for pineapple and banana were isolated from their root systems in different sites in Martinique including organic and i ntensive cropping systems. They are currently being identified (MIDI - FAME and ADNr16S sequencing) and tested as ISR inducers. Our research aims at validating the hypothesis that efficient and consistent systemic resistances to pathogens can be achieved i n the field by using selected varieties tolerant to abiotic stresses.