S14 - Session P5 - Lettuce Fusarium oxysporum f. sp. lactucae, evolution of knowledge

Authors: Sophie Perrot *, Isabelle Serandat, Geoffrey Orgeur, Valérie Grimault, Mathieu Pel, Enrick Georges

Fusarium oxysporum f. sp. lactucae on lettuce creates a serious threat for growers and a challenge for breeders with three main topics: emergence of a new race , the possibility or not of seed transmission and treatment. A new race of Fusarium , race 4, has been described . Previous studies conducted by GEVES for ISF had shown an absence of consistent results for isolates expected as race 4. An effect of environmental conditions was suspected. A joint ISF/IBEB initiative of comparison of isolates , in controlled and polytunnel conditions , began in 2021 bringing together 1 2 partners , with the objective to select a reference isolate of race 4 and to harmonise a protocol of evaluation of the resistance of lettuce to this new race 4. The Actifol project, funded as CASDAR by the French Ministry involving 9 partners , studies among other things, the possibility of seed transmission of Fusarium oxysporum f. sp. lactucae and the experimentation of alternatives methods of treatment against Fusarium on lettuce. The evaluation of seed transmission is conducted on commercial seed lots and on seeds harvested from artificial ly inoculated plants ( from susceptible, intermediate resistant and resistant varieties ). To date, of the 49 seed lots tested for detection of Fusarium , all have been negative (even those from artificially inoculated mother plants ). Other seed lots are still being harvest ed . Eight marketed products from different companies have been tested in controlled conditions with inoculation by Fusarium of a susceptible variety of lettuce to define the level of protection at the stage of transplantation of plantlets. One modality showed interesting level of protection. It was chosen in order to be test ed in field conditions.