Title : Fluorescents Pseudomonas isolates and aromatic plants extract to control bacterial canker of tomato disease in the central region of Morocco
Our research topic fits into the context of biological control which can be considered as a potential alternative to chemical control when used to control most of the diseases of vegetable crops including tomatoes. The studies conducted aimed at first the search and selection of fluorescent Pseudomonas antagonists to canker’s agent and secondly the assessment of natural substances extracted from plants for use in biological control against this disease. We have a collection of fluorescent Pseudomonas antagonists towards this pathogen and colonizing the roots of tomato plants. Antagonists selected isolates were screened using the cotyledons test. Eight isolates were selected after this test; they have significantly reduced the incidence of drying cotyledons compared to the positive control. The effectiveness of selected strains by previous tests is evaluated in pots in the greenhouse; the incidence of bacterial canker was reduced after bacterization of seeds and roots of tomato plants. The ability of the two best isolates (RN69 and RN39e) to protect against the invasion of tomato bacterial canker in the field was carried out. The results are very promising and they have confirmed that these two isolates of fluorescent Pseudomonas significantly reduce the incidence of disease compared to untreated controls. We could also see a very interesting PGPR effect especially in the early stages of culture. The in vitro action of some abiotic i.e.; temperature, pH and salts on the growth of the two best isolates RN39e and RN69 was evaluated. The results show that these two isolates have a wide range of resistance to tested factors. The genetic identification of isolates of Pseudomonas was achieved by sequencing the 16SrRNA and the rpoB genes. The results confirmed the heterogeneity of our collection because we have identified two main groups’ namely P. azotoformans and P. plecoglossicida. Another line is developed in terms of biological control against bacterial canker namely the use of extracts from southern Moroccan medicinal plants. The results obtained in this context are very interested. Indeed, in vitro tests with aqueous extracts of 40 plants of southern Morocco have shown inhibition zones of growth of the pathogen that are between 5 and 50 mm. The best results were obtained with the plants belonging to the genus Lavandula, Rubus, Rosa, Cistus, Pistacia and Anvillea. Treatment of tomato Seeds, infected with Cmm, with extracts of these plants do not have a negative impact on their ability to germinate and we even noticed a significant reduction in the population of the pathogen on the surface of treated seed. Preliminary phytochemical screening is performed for the 40 plants tested with TLC. The evaluation of flavonoid content, phenols content and the antioxidant activity was performed. The results showed that the best plants are rich in phenols compounds and flavonoids. A significant linear correlation was found between the biological activity, the antioxidant ability and richness with phenolic compounds. Another positive correlation was also found between the biological activity and the antioxidant ability.