Application of sonicated extracts of cyanobacteria and microalgae for the mitigation of bacterial canker in tomato seedlings

Microalgae and cyanobacteria could play an important role in crop protection, since they produce bioactive substances that promote plant growth and/or trigger the plant resistance mechanisms. The present study focuses on the control of bacterial canker caused by Clavibacter michiganensis subsp. michiganensis on tomato plants by using sonicated extracts from cyanobacteria and microalgae of the genera Leptolyngbya, Nostoc, Chlorella, and Scenedesmus. For the development of this study, 8 strains were firstly tested for their capacity to inhibit the growth of C. michiganensis subsp. michiganensis in vitro, as well as to produce cytokinins and salicylic acid. In order to discard those more phytotoxic strains, the germination index was also estimated in watercress seeds. Scenedesmus-677 and Leptolyngbya-1267 strains were selected in this first phase based on their pesticide and phytostimulant capacity in vitro. Subsequent bioassays on tomato seedlings showed that root application of Scenedesmus-677 could be more aimed at controlling the disease caused by C. michiganensis subsp. michiganensis, while foliar and root application of Leptolyngbya-1267 seems to be more related to the strengthening of the plant through the salicylic acid route. These preliminary results could serve as the basis for a deeper characterization of the biopesticidal and biostimulant effect of both strains, as well as to reveal the benefits derived from the combination of both capacities.