Taro leaf blight caused by Phytophthora colocasiae affects plant health and is a major threat to taro culture in Cameroon. Chemical fertilizers used often harm the ecosystem. Plant growth-promoting rhizobacteria (PGPR) are better alternatives that increase plant growth promotion and suppress phytopathogens. In the present study, a total of 67 fluorescent Pseudomonas spp. was characterized by 17.91, 5.97, and 4.47% populations of P. fluorescens, P. chlororaphis, and P. putida, respectively, among the most represented. More than 36% of bacteria showed antagonistic potential through the production of both diffusible and volatile compounds. Some of them (03) exhibited antagonistic activity in dual culture against P. colocasiae with a diameter greater than 13 mm. These rhizobacteria produced a significant amount of siderophore, IAA, SA, HCN, protease, lipases, and cellulases. For the pot experiment, treatment by Pseudomonas significantly increased the enzymatic activity involved in the resistance of taro, such as peroxidase (PO), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL). The two antagonists also increased plant growth parameters of taro such as chlorophyll, plant height, shoot length, total leaf surface, fresh root biomass, and fresh leaf biomass. These findings showed that fluorescent Pseudomonas have an intriguing and undeniable potential in the fight against P. colocasiae, which could lead to the development of a biopesticide in the future.

This work aimed to evaluate the potential of Trichoderma asperellum organic extract and its emulsion to control cocoa black pod disease caused by Phytophthora megakarya. Organic extract was obtained after fermentation of T. asperellum and its emulsion prepared by emulsification. The in vitro antimicrobial assays of organic extract and its emulsion were evaluated and the in situ tests were carried out on detached cocoa pods. T. asperellum inhibited the mycelia growth of P. megakarya at the rates of 52% and 100%, respectively, on dual culture and the cellophane plate. This antagonist produced lytic enzymes such as cellulase, amylase, lipase and protease. The organic extract contained alkaloid, flavonoid and phenol compounds. The emulsion obtained was stable. At 100 μg · ml ^-1, the extract and its formulation completely inhibited the mycelial growth of P. megakarya. Similarly, when infected detached cocoa pods were sprayed with extract or emulsion, there was a significant reduction of necrosis both for healing and prevention with the latter being the most efficient. For the preventive tests, the total inhibition was recorded at 3000 μg · ml ^-1 and 1000 μg · ml ^-1, respectively, with crude organic extract and its emulsion· For curative tests, total inhibition was obtained at 4000 μg · ml ^-1 and 3000 μg · ml ^-1, respectively, for preventive and curative tests. There was a significant and positive correlation between the content of biochemical markers and the reduction of necrosis on cocoa pods after treatment with the extract or its formulation. T. asperellum organic extract emulsion could be used as an alternative in the bio- protection of cocoa black pods disease.