Fungal metabolites for the biocontrol of Xylella fastidiosa

Xylella fastidiosa is a Gram-negative bacterium causing devastating diseases of many plants, including important crops as grapevine, peach, citrus, almond, coffee and pear. In the last decade, X. fastidiosa has devastated olive heritage in Apulia region (Italy) inducing a severe disease called “Olive Quick Decline Syndrome” The disease also infected millennial olive plants. The bacterium was introduced in this region from abroad and rapidly spread causing heavy economical losses and cultural and social damages. The eradication of infected plants in the restricted area at beginning of infection could be an effective approach to eliminate the bacterium. Unfortunately, this method was too late and partially applied. Studies carried out successively demonstrated that a zinc-copper-citric acid bio-complex allowed a consistent reduction of the infection on olive trees. The use of synthetic bactericides was discouraged as their use could cause resistance in the host plants and because of the long term impact of residues in agricultural products with a risk to human and animal health. Thus, a valid alternative could be the use of natural antibacterial metabolites. Some year ago, radicinin, a pihydropyranopyran-4,5-dione, was proposed as natural pesticide to control the infection of X. fastidiosa causing grapevines (Vitis vinifera L.) Pierce’s disease. Recently, radicinin together with some analogues were isolated from Cochliobolus australiensis, a fungus proposed as mycoherbicide to control buffelgrass (Cenchrus chliaris) an invasive weed in North America. The fungal production of radicinin was very low and this prompted the development of an efficient and ecofriendly total synthesis that afforded in good yield its biosynthetic precursor 3-deoxyradicinin. Further studies showed that 3-deoxyradicin displays phytotoxic activity against buffelgrass  and antibacterial activity against X. fastidiosa comparable with those of radicinin. These results allowed us propose both radicinin and 3-deoxyradicinin as potential natural pesticides which, conveniently bioformulated could be used to control of X. fastidiosa.